U.S. patent number 8,611,987 [Application Number 12/818,587] was granted by the patent office on 2013-12-17 for method and device for assisting in determination of the suitability of a patient for a scan of the patient's heart using an x-ray computer tomograph and method and x-ray computer tomograph for scanning the heart of a patient.
This patent grant is currently assigned to Siemens Aktiengesellschaft. The grantee listed for this patent is Thomas Allmendinger, Heiko Mehldau, Thomas Seiler, Carsten Thierfelder. Invention is credited to Thomas Allmendinger, Heiko Mehldau, Thomas Seiler, Carsten Thierfelder.
United States Patent |
8,611,987 |
Allmendinger , et
al. |
December 17, 2013 |
Method and device for assisting in determination of the suitability
of a patient for a scan of the patient's heart using an X-ray
computer tomograph and method and X-ray computer tomograph for
scanning the heart of a patient
Abstract
A method is disclosed for assisting in determination of the
suitability of a patient for a scan of the heart of the patient
using an X-ray computer tomograph. In at least one embodiment of
the method, a) an electrocardiogram of the patient is recorded; b)
the electrocardiogram is evaluated by predicting the occurrence
time of at least the immediately following R wave on the basis of
at least four immediately consecutive R waves of the
electrocardiogram which were measured last, and comparing this with
the actual measured occurrence time of the next R wave; and c)
wherein the quality of the prediction is visualized qualitatively.
Further, in at least one embodiment, a device is disclosed
including an ECG instrument and a computation device for carrying
out the method. At least one embodiment of the invention
furthermore relates to a method and a device for scanning the heart
of a patient on the basis of a prediction of R waves.
Inventors: |
Allmendinger; Thomas (Forcheim,
DE), Mehldau; Heiko (Nurnberg, DE), Seiler;
Thomas (Buckenhof, DE), Thierfelder; Carsten
(Pinzberg, DE) |
Applicant: |
Name |
City |
State |
Country |
Type |
Allmendinger; Thomas
Mehldau; Heiko
Seiler; Thomas
Thierfelder; Carsten |
Forcheim
Nurnberg
Buckenhof
Pinzberg |
N/A
N/A
N/A
N/A |
DE
DE
DE
DE |
|
|
Assignee: |
Siemens Aktiengesellschaft
(Munich, DE)
|
Family
ID: |
43123094 |
Appl.
No.: |
12/818,587 |
Filed: |
June 18, 2010 |
Prior Publication Data
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|
Document
Identifier |
Publication Date |
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US 20100324434 A1 |
Dec 23, 2010 |
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Foreign Application Priority Data
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Jun 22, 2009 [DE] |
|
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10 2009 030 109 |
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Current U.S.
Class: |
600/425; 600/427;
600/407; 378/11; 600/428; 378/4; 600/426; 378/20; 600/429 |
Current CPC
Class: |
A61B
6/541 (20130101); A61B 5/352 (20210101); A61B
6/503 (20130101) |
Current International
Class: |
A61B
5/05 (20060101) |
Field of
Search: |
;600/407,425,426,427,428,429 ;378/4,11-20 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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102005012386 |
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Sep 2006 |
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DE |
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102005027944 |
|
Jan 2007 |
|
DE |
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102007051548 |
|
Jun 2009 |
|
DE |
|
Other References
Russo et al., "How Fluent is Your Interface? Designing for
International Users" Apr. 1993, Interchi '93, p. 342-347. cited by
examiner.
|
Primary Examiner: Kish; James
Attorney, Agent or Firm: Harness, Dickey & Pierce,
P.L.C.
Claims
What is claimed is:
1. A method for assisting in determination of the suitability of a
patient for a scan of a heart of the patient in a resting phase of
only one cardiac cycle of the patient's heart using an X-ray
computer tomograph, the method comprising: recording an
electrocardiogram of the patient; evaluating, by a processor, the
electrocardiogram by predicting an occurrence time of at least an
immediately following R wave based upon at least four immediately
consecutive R waves of the electrocardiogram which were previously
measured; comparing, by the processor, the occurrence time with an
actual measured occurrence time of the next R wave to obtain an
accuracy of the prediction; determining, by the processor, a
quality of the prediction by comparing the accuracy with a
threshold; and displaying, by the processor, the quality of the
prediction.
2. The method as claimed in claim 1, wherein the recording of the
electrocardiogram is performed while the patient stops breathing,
only a part of the electrocardiogram which is recorded while the
patient has stopped breathing for at least one of two to five
cardiac cycles and three to four seconds is used in the
evaluating.
3. The method as claimed in claim 2, wherein in the evaluating, the
occurrence times of the immediately following fifth and sixth waves
are predicted on a basis of a first, a second, a third and a fourth
immediately consecutive measured R waves of the electrocardiogram,
and compared with the actual measured occurrence times of the
immediately following fifth and sixth waves.
4. The method as claimed in claim 1, wherein in the evaluating, the
occurrence times of immediately following fifth and sixth R waves
are predicted on a basis of a first, a second, a third and a fourth
immediately consecutive measured R waves of the electrocardiogram,
and compared with the actual measured occurrence times of the
immediately following fifth and sixth waves.
5. The method as claimed in claim 1, wherein the evaluating is
carried out repeatedly in order to determine the quality of the
prediction.
6. The method as claimed in claim 3, wherein the evaluating is
carried out in an overlapping fashion in relation to the R waves,
an advance by one R wave taking place each time the evaluating is
carried out.
7. The method as claimed in claim 1, wherein a prediction of the
occurrence time of an R wave is classed as adequate if a difference
between the predicted time and the actual measured occurrence time
of the R wave is less than 5%.
8. The method as claimed in claim 7, wherein the quality of the
prediction is visualized green overall if the relevant predictions
have predominantly been classed as adequate, and wherein the
quality of the predictions is visualized red overall if the
relevant predictions have predominantly been classed as too
inaccurate.
9. A method for recording 2D X-ray projections of a heart of a
patient from different projection directions in a resting phase of
only one cardiac cycle of the patient using an X-ray computer
tomograph, the method comprising: determining a suitability of the
patient, for recording of 2D X-ray projections of the heart of the
patient in the resting phase of only one cardiac cycle of the heart
of the patient, according to the method as claimed in claim 1;
obtaining an electrocardiogram of the patient using an ECG
instrument; predicting occurrence times of immediately following
fifth and sixth R waves based upon a first, a second, a third and a
fourth immediately consecutive measured R waves of the
electrocardiogram of the patient; and starting the recording of the
2D X-ray projections of the heart of the patient in the predicted
cardiac cycle lying between the predicted fifth and sixth R
waves.
10. The method as claimed in claim 9, wherein the start of the
recording of the 2D X-ray projections of the heart of the patient
takes place at about 50% to 60% of the predicted cardiac cycle.
11. The method as claimed in claim 10, wherein the recording of the
2D X-ray projections of the heart of the patient is ended at about
90% of the predicted cycle.
12. The method as claimed in claim 10, wherein the visualizing
represents the suitability of the patient for a subsequent scan of
the heart.
13. The method as claimed in claim 9, wherein the recording of the
2D X-ray projections of the heart of the patient is ended at about
90% of the predicted cardiac cycle.
14. The method as claimed in claim 9, wherein at least one of a 2D
slice image and a 3D data set of the heart of the patient is
reconstructed based on the 2D X-ray projections recorded in the
resting phase of the heart of the patient.
15. A device, comprising: an ECG instrument; and an X-ray computer
tomograph, wherein a computation device of the X-ray computer
tomograph carries out the method as claimed in claim 9.
16. A non-transitory computer readable medium including a computer
program product, the computer program product comprising
instructions, which when executed on a computer device, causes the
computer device to implement the method of claim 9.
17. A non-transitory computer readable medium including a computer
program product, the computer program product comprising
instructions, which when executed on a computer device, causes the
computer device to implement the method of claim 1.
18. A device, comprising: an electrocardiogram (ECG) instrument
configured to record an electrocardiogram of a patient; and a
computation device configured to, record an electrocardiogram of a
patient, evaluate the electrocardiogram by predicting an occurrence
time of at least an immediately following R wave based upon at
least four immediately consecutive R waves of the electrocardiogram
which were previously measured, compare the occurrence time with an
actual measured occurrence time of the next R, wave to obtain an
accuracy of the prediction; determining a quality of the prediction
by comparing the accuracy with a threshold; and displaying the
quality of the prediction.
Description
PRIORITY STATEMENT
The present application hereby claims priority under 35 U.S.C.
.sctn.119 on German patent application number DE 10 2009 030 109.7
filed Jun. 22, 2009, the entire contents of which are hereby
incorporated herein by reference.
FIELD
At least one embodiment of the invention generally relates to a
method and/or a device for assisting in determination of the
suitability of a patient for a scan of the patient's heart using an
X-ray computer tomograph, wherein a doctor is provided with a basis
for the decision whether the scan is carried out or is better
omitted. At least one embodiment of the invention furthermore
generally relates to a method and an X-ray computer tomograph for
scanning a patient' heart.
BACKGROUND
Patients with heart diseases, in so far as is medically necessary
and expedient, are subjected to scans using X-ray computer
tomographs in order to examine the heart, a scan being intended to
mean recording a multiplicity of 2D X-ray projections of the heart
from different projection directions, usually with an incremental
advance of the heart or the patient relative to the X-ray recording
system of the X-ray computer tomograph. The purpose of the
examination is to generate high-quality and informative images of
the heart, which often form the basis for a diagnosis.
Since the heart is a moving organ, when reconstructing slice images
and 3D images of the heart, which is done on the basis of the
recorded 2D X-ray projections of the heart, attempts are made to
use only those 2D X-ray projections that have been recorded in the
cardiac phase of the patient's cardiac cycle in which the heart has
performed almost no movement, particularly in order to avoid motion
artifacts in the reconstructed slice images and 3D images of the
heart. In order to determine the cardiac cycle of the patient's
heart, it is usual to record an electrocardiogram (ECG) of the
patient's heart.
For producing slice images and 3D images of the heart, 2D X-ray
projections of the heart are recorded over several cardiac cycles
with parallel recording of the electrocardiogram, and subsequently
only the 2D X-ray projections suitable for the reconstruction are
selected on the basis of the electrocardiogram, for which reason
this is also referred to as a retrospective method.
In an alternative procedure, 2D X-ray projections of the heart are
likewise obtained over several cardiac cycles, but on the basis of
an electrocardiogram recorded in parallel only if the heart is in a
cardiac phase for which it performs almost no movement. This
procedure has the advantage that the patient is exposed to a lower
X-ray dose.
Obtaining 2D X-ray projections of the heart over several cardiac
cycles has been or is necessary since not enough 2D X-ray
projections from different projection directions of the patient's
heart could be obtained with the previously available X-ray
computer tomographs within only one resting phase of the patient's
cardiac cycle, in order to reconstruct high-quality slice images
and 3D images of the heart. The reason for this resides in the
limited rotation speed of the gantry rotating around the patient
and comprising the X-ray system, as well as the limited
acceleration and adjustment speed of the patient table supporting
the patient.
Recently, however, X-ray computer tomographs, in particular X-ray
computer tomographs having two X-ray systems arranged on a gantry
and offset by about 90.degree., have become available, with which
it is possible to obtain enough 2D X-ray projections from different
projection directions within the resting phase of only one cardiac
cycle of a patient's heart, so that high-quality slice images and
3D images of the patient's heart can be reconstructed. Patients who
are viable for a successful examination using such X-ray computer
tomographs, however, are subject to certain physiological
restrictions, particularly in relation to the duration of the
cardiac cycle and the tolerable variance of the cardiac cycle.
SUMMARY
In at least one embodiment of the invention, a method and a device
are provided, so as to provide a basis for a decision whether the
scan can be carried out successfully in only one resting phase of a
patient's part. Furthermore, in at least one embodiment of the
invention, a suitable method and an X-ray computer tomograph are
provided for scanning the patient's heart in only one resting phase
of the heart.
According to at least one embodiment of the invention, a method is
disclosed for assisting in determination of the suitability of a
patient for a scan of the patient's heart using an X-ray computer
tomograph.
At least one embodiment of the method is based on the idea that for
the intended scan of the heart, in which the 2D X-ray projections
are recorded from different directions of the patient's heart in
the resting phase of only one cardiac cycle of the patient's heart
in order to reconstruct slice images and/or 3D images of the heart,
it is necessary to establish whether the patient intended for the
scan, or the patient's heart, exhibits a suitable cardiac cycle and
a tolerable variance of the cardiac cycle so that the scan can be
carried out successfully within the resting phase of only one
cardiac cycle of the patient. If the heart rate or the variance of
the patient's cardiac cycle is too high, the patient is not
suitable for said scan and an alternative scanning method should be
selected.
In order to be able to record the 2D X-ray projections of the
patient's heart in only one resting phase of the heart, it must be
possible for the starting time of the scan in the resting phase of
the patient's heart to be predicted comparatively stably. For this
reason, in order to determine the heart rate and the cardiac cycle
of the patient, an electrocardiogram of the patient's heart is
initially recorded in a method step a).
This electrocardiogram is evaluated by predicting the occurrence
time of at least the immediately following R wave on the basis of
at least four immediately consecutive R waves of the
electrocardiogram which were measured last, and comparing this with
the actual measured occurrence time of the next R wave. From
comparison of the result of the prediction and the measured
occurrence of the next R wave, a quality of the prediction can be
determined. If the prediction is in a predeterminable tolerance
range, the prediction is acceptable and the patient's cardiac cycle
is such that at least the occurrence time of the R wave following
four previously measured R waves or three previously measured
cardiac cycles or cycle lengths can be predicted for the patient in
question with sufficient accuracy so that the starting time of the
scan can also be established per se. This fact or the suitability
in principle, or possibly the unsuitability, is finally visualized
so that for example a doctor can make the decision about carrying
out the scan while taking into account other aspects relating to
the patient if appropriate.
According to a variant of at least one embodiment of the invention,
the patient is requested to hold his breath while the
electrocardiogram is being recorded, only that part of the
electrocardiogram which is recorded while the patient has been
holding his breath for two to five cardiac cycles and/or three to
four seconds being employed for the evaluation. It has been found
that holding the breath as a positive effect on the heart rate and
the variability of the heart rate. Thus, when a patient is holding
his breath, the heart rate is generally three to ten heart beats
less than the heart rate encountered when the patient is breathing
freely. The variance of the heart rate furthermore decreases when
the breath is being held, which improves the stability of the
prediction of R waves. Since immediately after he starts to hold
his breath, depending on the patient, the heart rate does however
increase for about two to five cardiac cycles, or when he is
holding his breath it takes about three to four seconds until the
patient's heart rate is equilibrated or stable, the part of the
electrocardiogram which is recorded after this time is first waited
for.
According to one embodiment of the invention, in method step b) the
occurrence times of the immediately following x(t+1).sup.th R wave
and the x(t+2).sup.th R wave are predicted on the basis of an
x(t-3).sup.th, an x(t-2).sup.th, an x(t-1).sup.th and an
x(t).sup.th immediately consecutive measured R wave of the
electrocardiogram, and compared with the actual measured occurrence
times of the immediately following x(t+1).sup.th R wave and
x(t+2).sup.th R wave.
Preferably, method step b) is carried out repeatedly in order to
determine the quality of the prediction. According to another
embodiment of the invention, method step b) is carried out several
times in succession or in an overlapping fashion in relation to the
R waves, an advance by one R wave taking place each time it is
carried out.
For example, the occurrence times of the immediately following
fifth and sixth R waves are predicted on the basis of a first, a
second, a third and a fourth immediately consecutive measured R
wave of the electrocardiogram, and compared with the actual
measured occurrence times of the immediately following fifth and
sixth R waves. In continuation of at least one embodiment of the
method, the occurrence times of the immediately following sixth and
seventh R waves are predicted on the basis of the second, the
third, the fourth and the fifth immediately consecutive measured R
waves of the electrocardiogram, and compared with the actual
measured occurrence times of the immediately following sixth and
seventh R waves. Lastly, the occurrence times of the immediately
following seventh and eighth R waves are predicted on the basis of
the third, the fourth, the fifth and the sixth immediately
consecutive measured R waves of the electrocardiogram, and compared
with the actual measured occurrence times of the immediately
following seventh and eighth R waves.
In this way, a plurality of predictions are obtained for the
occurrence times of R waves, and by comparing these with the actual
occurrence times of the respective R wave the quality of the
prediction individually and/or the quality of the prediction in
total can be determined and visualized.
According to a variant of at least one embodiment of the invention,
a prediction of the occurrence time of an R wave is classed as
adequate or acceptable if the difference between the time
prediction and the actual measured occurrence time of the R wave is
less than 5%.
According to one embodiment of the invention, the quality of the
prediction or predictions is visualized green overall if the
relevant predictions have predominantly been classed as adequate,
and it is visualized red overall if the relevant predictions have
predominantly been classed as too inaccurate. Visualization with
the color green means that the patient in question is classed as
suitable for the intended scan, since the occurrence times of R
waves can be predicted comparatively stably. Visualization with the
color red means that the patient in question is classed as not
suitable for the intended scan. The final decision about carrying
out the scan, however, lies with the doctor in charge.
At least one embodiment of the present invention is also directed
to a device that has an ECG instrument and computation means, which
are adapted to carry out one of the methods above. To this end, the
computation devices are preferably provided with corresponding
software or corresponding software modules, so that the method can
be carried out in an automated fashion.
At least one embodiment of the invention is directed to a method
for recording 2D X-ray projections of a patient's heart from
different projection directions in the resting phase of only one
cardiac cycle of the patient using an X-ray computer tomograph,
wherein the patient's suitability for the recording of 2D X-ray
projections of the patient's heart in the resting phase of only one
cardiac cycle of the patient's heart is initially determined
according to the one of the methods described above, an
electrocardiogram of the patient's heart is obtained using an ECG
instrument, the occurrence times of the immediately following fifth
and sixth R waves are predicted on the basis of a first, a second,
a third and a fourth immediately consecutive measured R wave of the
patient's electrocardiogram, and wherein the start of the recording
of the 2D X-ray projections of the patient's heart takes place in
the predicted cardiac cycle lying between the predicted fifth and
sixth R waves. According to at least one embodiment of the
invention, the occurrence of the next but one cardiac cycle is thus
predicted on the basis of four measured R waves or three measured
cardiac cycles or cycle lengths, and the scan of the heart is
started in the predicted cardiac cycle.
Preferably, the start of the scan, or the start of recording the 2D
X-ray projections of the patient's heart, takes place at about 50%
to 60% of the predicted cardiac cycle. According to a variant of at
least one embodiment of the invention, the scan, or the recording
of the 2D X-ray projections of the patient's heart, is ended at
about 90% of the predicted cardiac cycle. Here, the resting phase
of the heart lies between 50% and 90% of the predicted cardiac
cycle.
According to one embodiment of the invention, at least one 2D slice
image and/or a 3D data set of the patient's heart is reconstructed
only on the basis of the 2D X-ray projections recorded in a resting
phase of the patient's heart. In the resting phase of the heart, it
is thus possible to record enough 2D X-ray projections so that
high-quality 2D slice images and/or a high-quality 3D data set can
be reconstructed.
At least one embodiment of the invention is also achieved by a
device having an ECG instrument and an X-ray computer tomograph,
wherein computation devices of the X-ray computer tomograph are
adapted to carry out one of the methods described above with
corresponding software.
BRIEF DESCRIPTION OF THE DRAWINGS
An example embodiment of the invention is represented in the
appended schematic drawings, in which:
FIG. 1 shows an X-ray computer tomograph for carrying out a scan of
a patient's heart,
FIG. 2 shows a cardiac cycle of a human heart,
FIG. 3 shows an illustration of the prediction of R waves and
FIG. 4 shows an illustration of the calculation of the scan
start.
DETAILED DESCRIPTION OF THE EXAMPLE EMBODIMENTS
Various example embodiments will now be described more fully with
reference to the accompanying drawings in which only some example
embodiments are shown. Specific structural and functional details
disclosed herein are merely representative for purposes of
describing example embodiments. The present invention, however, may
be embodied in many alternate forms and should not be construed as
limited to only the example embodiments set forth herein.
Accordingly, while example embodiments of the invention are capable
of various modifications and alternative forms, embodiments thereof
are shown by way of example in the drawings and will herein be
described in detail. It should be understood, however, that there
is no intent to limit example embodiments of the present invention
to the particular forms disclosed. On the contrary, example
embodiments are to cover all modifications, equivalents, and
alternatives falling within the scope of the invention. Like
numbers refer to like elements throughout the description of the
figures.
It will be understood that, although the terms first, second, etc.
may be used herein to describe various elements, these elements
should not be limited by these terms. These terms are only used to
distinguish one element from another. For example, a first element
could be termed a second element, and, similarly, a second element
could be termed a first element, without departing from the scope
of example embodiments of the present invention. As used herein,
the term "and/or," includes any and all combinations of one or more
of the associated listed items.
It will be understood that when an element is referred to as being
"connected," or "coupled," to another element, it can be directly
connected or coupled to the other element or intervening elements
may be present. In contrast, when an element is referred to as
being "directly connected," or "directly coupled," to another
element, there are no intervening elements present. Other words
used to describe the relationship between elements should be
interpreted in a like fashion (e.g., "between," versus "directly
between," "adjacent," versus "directly adjacent," etc.).
The terminology used herein is for the purpose of describing
particular embodiments only and is not intended to be limiting of
example embodiments of the invention. As used herein, the singular
forms "a," "an," and "the," are intended to include the plural
forms as well, unless the context clearly indicates otherwise. As
used herein, the terms "and/or" and "at least one of" include any
and all combinations of one or more of the associated listed items.
It will be further understood that the terms "comprises,"
"comprising," "includes," and/or "including," when used herein,
specify the presence of stated features, integers, steps,
operations, elements, and/or components, but do not preclude the
presence or addition of one or more other features, integers,
steps, operations, elements, components, and/or groups thereof.
It should also be noted that in some alternative implementations,
the functions/acts noted may occur out of the order noted in the
figures. For example, two figures shown in succession may in fact
be executed substantially concurrently or may sometimes be executed
in the reverse order, depending upon the functionality/acts
involved.
Spatially relative terms, such as "beneath", "below", "lower",
"above", "upper", and the like, may be used herein for ease of
description to describe one element or feature's relationship to
another element(s) or feature(s) as illustrated in the figures. It
will be understood that the spatially relative terms are intended
to encompass different orientations of the device in use or
operation in addition to the orientation depicted in the figures.
For example, if the device in the figures is turned over, elements
described as "below" or "beneath" other elements or features would
then be oriented "above" the other elements or features. Thus, term
such as "below" can encompass both an orientation of above and
below. The device may be otherwise oriented (rotated 90 degrees or
at other orientations) and the spatially relative descriptors used
herein are interpreted accordingly.
Although the terms first, second, etc. may be used herein to
describe various elements, components, regions, layers and/or
sections, it should be understood that these elements, components,
regions, layers and/or sections should not be limited by these
terms. These terms are used only to distinguish one element,
component, region, layer, or section from another region, layer, or
section. Thus, a first element, component, region, layer, or
section discussed below could be termed a second element,
component, region, layer, or section without departing from the
teachings of the present invention.
FIG. 1 shows an X-ray computer tomograph 1 which, in a housing 2,
has a gantry 3 which can be rotated about a symmetry axis 8
relative to the housing 2 and on which two X-ray systems are
arranged offset relative to one another by about 90.degree.. The
first X-ray system has an X-ray source 4 and an X-ray detector 5
lying opposite one another, and the second X-ray system has an
X-ray source 6 and an X-ray detector 7 lying opposite one another.
The central beam of the X-ray bundle coming from the first X-ray
source 4 and the central beam of the X-ray bundle coming from the
second X-ray source 6 intersect approximately at a 90.degree. angle
on the symmetry axis 8 of the X-ray computer tomograph 1. During
operation, X-radiation travels from the X-ray source 4 in the
direction of the X-ray detector 5 and X-radiation travels from the
X-ray source 6 in the direction of the X-ray detector 7, this
radiation being recorded by the X-ray detectors 5 and 7,
respectively.
In the case of the present example embodiment of the invention, the
patient support plate 9 of a patient table 10 of the X-ray computer
tomograph 1 supports a patient P, from whose heart 2D X-ray
projections are intended to be recorded from different projection
directions in only one resting phase of the cardiac cycle of the
patient P using the X-ray computer tomograph 1, in order to
reconstruct 2D slice images and/or 3D images of the heart of the
patient P. To this end, the patient support plate 9 is adjusted or
moved so that the 2D X-ray projections of the heart of the patient
P can be recorded for example in a spiral scan.
The computational processing of the 2D X-ray projections which are
recorded using the two X-ray systems, or the reconstruction of
slice images and/or 3D images on the basis of the 2D X-ray
projections, is carried out using a schematically represented
computer 12 of the X-ray computer tomograph 1, which slice images
or 3D images can be represented on a display device 13.
The X-ray computer tomograph 1 may for example be a Somatom
Definition Flash computer tomograph from Siemens AG, the gantry of
which has a rotation time of about 0.28 seconds and the patient
support plate of which has an adjustment speed of up to 43
cm/second.
Regarding the cardiac cycle of a human recorded by an ECG
instrument, as shown in FIG. 2, this has characteristic waves
denoted by P, Q, R and T, and sections lying between the waves.
Here, what is important is the time between two successive R waves
and the section denoted by M between the T and P waves, which
represents the phase of the heart in which it performs almost no
movement and in which 2D X-ray projections of the heart are
preferably recorded for imaging the heart.
The cardiac cycle of a healthy human is such that a full scan of
the heart can be carried out in only one resting phase M of the
cardiac cycle, for example using the Somatom Definition Flash
computer tomograph from Siemens AG, this requiring only about 250
milliseconds with the Somatom Definition Flash. Specifically for
patients with heart diseases, however, the cycle time may be
shortened or the cardiac cycle may have a strong variability, so
that before such a scan of a patient's heart it is necessary to
ascertain the patient's suitability in principle for this type of
scan. In particular, the purpose of this is to avoid scans of this
type which cannot be carried out successfully, and therefore an
unnecessary radiation dose for patients.
In the case of the present example embodiment of the invention, the
patient P is therefore provided with ECG electrodes (not shown
explicitly) and connected to an ECG instrument 14, which is linked
to the computer 12 of the X-ray computer tomograph 1. An ECG of the
heart of the patient P is recorded using the ECG instrument 14, and
evaluated in order to assist in determining the suitability of the
patient P for the scan in only one resting phase of the heart of
the patient P using the X-ray computer tomograph 1.
After the start of recording the ECG using the ECG instrument 14,
in the case of the present example embodiment of the invention the
patient P is requested to hold his breath, the advantage of which
is that the heart rate when the breath is being held is generally
about three to ten heart beats less than the heart rate encountered
when breathing freely. The variance of the heart rate furthermore
decreases when the breath is being held. Before the evaluation of
the ECG begins, after the instruction to hold his breath, about two
to five cardiac cycles or about three to four seconds are
furthermore waited until the heart rate of the patient P is
equilibrated or stable.
In principle, it is also possible for the ECG when the patient P is
breathing freely to be evaluated in relation to the suitability of
the patient P for the scan, a scan is also possible when the
patient P is breathing freely. Besides the associated positive
aspects i.e. the aforementioned lower heart rate and the lower
variance of the heart rate, however, holding the breath is an
everyday established clinical working procedure which is also
practiced in other examinations of patients using computer
tomographs, for example for obtaining a topogram of the patient or
in examinations in which contrast agents are applied, for which
reason this procedure is described in the case of the present
example embodiment.
Once the two to five cardiac cycles and/or three to four seconds
have elapsed after the patient has started to hold his breath, the
software-controlled evaluation of the ECG of the patient P is
carried out using the computer 12, which is provided with
corresponding software. FIG. 3 illustrates the evaluation of the
ECG in the case of the present example embodiment of the
invention.
In the automatic software-controlled evaluation of the ECG, the
occurrence time (t-3) of a first R wave R1, the occurrence time
(t-2) of a second R wave R2, the occurrence time (t-1) of a third R
wave R3 and the occurrence time (t) of a fourth R wave R4 are
registered while recording the ECG. During the further recording of
the ECG, the occurrence time of the fifth R wave R5 following the
fourth R wave R4 and the sixth R wave R6 immediately
chronologically following the fifth R wave R5 are predicted or
determined on the basis of the four said times of the four
registered R waves R1 to R4, or the three measured cardiac cycles
or cycle lengths. The determination is carried out in the time
interval between the occurrence of the fourth R wave R4 and the
fifth R wave R5.
The determination of the cycle lengths or cycle times between the R
waves R4 and R5, and R5 and R6, or the determination of the
occurrence times of the R waves R5 and R6 on the basis of the
determination of the cycle lengths or cycle times between the R
waves R4 and R5, and R5 and R6, may be carried out with the aid of
a median filter ME whose input values are the cycle times between
the R waves R1 and R2, R2 and R3, and R3 and R4. When the cycle
time determined using the median filter ME is added to the time of
the last measured R wave R4, the prediction for the occurrence time
of the R wave R5 is obtained, and when it is added twice the
prediction for the occurrence time of the R wave R6 is
obtained.
This determination can be made more precise by determining the
linear trend of these three cardiac cycles in parallel with the aid
of a linear regression. On the basis of this, a trend line with a
slope a and an intercept b can be determined, and a standard
deviation of the measured cycle times can be determined from the
trend line. Taking into account a weight w which is based on the
standard deviation and whose value lies between zero and one, in
the present case the cycle lengths or cycle times between the R
waves R4 and R5 are determined here as C1=w*(b)+(1-w)*ME, and
between the R waves R5 and R6 as C2=w*(a+b)+(1-w)*ME. This gives
the occurrence time of the R wave R5 as R5=R4+C1 and the occurrence
time of the R wave R6 as R6=R4+C1+C2.
When the fifth R wave R5 is registered, its occurrence time is
compared with the predicted occurrence time of the fifth R wave R5.
If the difference between the predicted occurrence time of the
fifth R wave R5 and the actual occurrence time of the fifth R wave
R5 is less than 5%, the prediction is classed as adequate or
acceptable.
Once the fifth R wave R5 has been registered, in the scope of the
software-controlled evaluation of the patient's ECG the occurrence
times of the sixth R wave R6 and the seventh R wave R7 are
predicted as explained above on the basis of the respective
occurrence times of the second R wave R2, the third R wave R3, the
fourth R wave R4 and the fifth R wave R5.
Finally, when the occurrence time of the sixth R wave R6 is
registered, two comparison values are available for it. In respect
of a first run D1, the actual occurrence time of the sixth R wave
R6 is compared with the time prediction of the occurrence of the
sixth R wave R6 based on the R waves R1 to R4, and in respect of a
second run D2 the actual occurrence time of the sixth R wave R6 is
compared with the time prediction of the occurrence of the sixth R
wave R6 based on the R waves R2 to R5. For both cases, whether the
difference between the respective prediction and the actual
occurrence time of the sixth R wave R6 is less than 5% is
determined. This furthermore provides an estimate of the stability
of the heart rate of the patient P, i.e. whether a comparatively
reliable prediction of the next but one R wave is actually
possible.
In the same way, further runs D3 and D4 or mutually overlapping
predictions are carried out, an advance by one R wave that has
occurred taking place each time a prediction is carried out. Thus,
the occurrence times of the R waves R7 and R8 are predicted on the
basis of the measured occurrence times of the R waves R3 to R6, the
occurrence times of the R waves R8 and R9 are predicted on the
basis of the measured occurrence times of the R waves R4 to R7,
etc., and in each case checked in relation to their acceptance.
As a result of the method, the quality of the predictions in total
is finally determined and visualized. If the predictions have
predominantly been acceptable, the quality of the prediction is
visualized with the color green or a green light, for example as a
green traffic light, so as to indicate that the patient is classed
as suitable for the intended scan. If the predictions have
predominantly not been acceptable, the quality of the prediction is
visualized with the color red or a red light, for example as a red
traffic light, so as to indicate that the patient is classed as not
suitable for the intended scan. The quality may respectively be
displayed on the viewing instrument 13.
Taking into account further aspects relating to the patient, a
doctor therefore has a basis for making a decision whether a scan,
in which 2D X-ray projections of the heart of the patient P are
recorded from different projection directions in only one resting
phase of the heart, should be carried out for the patient P. If a
topogram of the heart of the patient P has previously been recorded
with the patient P holding his breath, the region of the heart
which is scanned in the interval between two predicted R waves may
be indicated graphically in the topogram.
When suitability of the patient P in principle for the scan has
been established, and the decision for the scan has been made, the
adjustments of the X-ray computer tomograph 1, for example the
speed of the forward increment of the patient support plate 9, the
rotation speed of the gantry 3 etc. are carried out individually
for the scan of the patient P so that, on the basis of the
currently recorded ECG of the patient P and the occurrence times of
two R waves predicted on the basis of the ECG, the scan of the
patient begins at about 50%-60% of the interval between the two
predicted R waves and ends at about 90% of the interval between the
two predicted R waves.
On the basis of four occurrence times of R waves, in the present
case the occurrences of the following two R waves are thus
predicted and the scan is carried out in the interval between the
two predicted R waves. To this end, the patient support plate 9
must be accelerated promptly so that it has reached the established
scan speed at the calculated time of the scan start.
If, in the event that a patient exhibits a heart rate which is
elevated but stable per se, the time for accelerating the patient
support plate 9 up to the planned scan start at about 50%-60% of
the interval between the two predicted R waves is not sufficient to
bring the patient support plate 9 to the speed required for the
scan, the start of the scan may also be shifted under software
control into the interval between two R waves following the
interval which has been determined. This will be illustrated
briefly with the aid of FIG. 4. R0 is the time of the R wave
measured last, R1' and R2' are the predicted times of the next two
R waves, P is the desired start phase of the scan at about 60% of
the interval between R1' and R2' and TT is the time which the
patient support plate 9 needs in order to have reached its final
speed or scan speed at the starting time TS of the scan. The scan
start time is given as TS=R1'+P*(R2'-R1') and the start time
derived therefrom for the patient support plate 9 is given as
TP=TS-TT. If the time TP now lies before R0, the scan would not be
possible with these parameters. In order to make the scan possible
in spite of this, as already mentioned, the scan start is placed
after R2' and the scan start time is selected as TS=R2'+C, where is
a time delay.
The time delay C is given on the basis of the patient's current
heart rate from a table which has been determined from empirical
values, i.e. a particular heart rate is assigned a particular time
delay C determined from empirical values.
The use of at least one embodiment of the invention has been
described above in connection with the Somatom Definition Flash
computer tomograph from Siemens AG. Embodiments of the invention
may, however, also be used with other computer tomographs which are
suitable for carrying out a scan of the heart within only one
resting phase of a patient's heart, while being based on reliable
predictions of two cardiac cycles.
The prediction of the occurrence times of R waves may be carried
out merely by using a median filter, or in combination with the
determination of a linear trend. The prediction may, however, be
carried out using other mathematical methods, for example by way of
an extrapolation.
The patent claims filed with the application are formulation
proposals without prejudice for obtaining more extensive patent
protection. The applicant reserves the right to claim even further
combinations of features previously disclosed only in the
description and/or drawings.
The example embodiment or each example embodiment should not be
understood as a restriction of the invention. Rather, numerous
variations and modifications are possible in the context of the
present disclosure, in particular those variants and combinations
which can be inferred by the person skilled in the art with regard
to achieving the object for example by combination or modification
of individual features or elements or method steps that are
described in connection with the general or specific part of the
description and are contained in the claims and/or the drawings,
and, by way of combinable features, lead to a new subject matter or
to new method steps or sequences of method steps, including insofar
as they concern production, testing and operating methods.
References back that are used in dependent claims indicate the
further embodiment of the subject matter of the main claim by way
of the features of the respective dependent claim; they should not
be understood as dispensing with obtaining independent protection
of the subject matter for the combinations of features in the
referred-back dependent claims. Furthermore, with regard to
interpreting the claims, where a feature is concretized in more
specific detail in a subordinate claim, it should be assumed that
such a restriction is not present in the respective preceding
claims.
Since the subject matter of the dependent claims in relation to the
prior art on the priority date may form separate and independent
inventions, the applicant reserves the right to make them the
subject matter of independent claims or divisional declarations.
They may furthermore also contain independent inventions which have
a configuration that is independent of the subject matters of the
preceding dependent claims.
Further, elements and/or features of different example embodiments
may be combined with each other and/or substituted for each other
within the scope of this disclosure and appended claims.
Still further, any one of the above-described and other example
features of the present invention may be embodied in the form of an
apparatus, method, system, computer program, computer readable
medium and computer program product. For example, of the
aforementioned methods may be embodied in the form of a system or
device, including, but not limited to, any of the structure for
performing the methodology illustrated in the drawings.
Even further, any of the aforementioned methods may be embodied in
the form of a program. The program may be stored on a computer
readable medium and is adapted to perform any one of the
aforementioned methods when run on a computer device (a device
including a processor). Thus, the storage medium or computer
readable medium, is adapted to store information and is adapted to
interact with a data processing facility or computer device to
execute the program of any of the above mentioned embodiments
and/or to perform the method of any of the above mentioned
embodiments.
The computer readable medium or storage medium may be a built-in
medium installed inside a computer device main body or a removable
medium arranged so that it can be separated from the computer
device main body. Examples of the built-in medium include, but are
not limited to, rewriteable non-volatile memories, such as ROMs and
flash memories, and hard disks. Examples of the removable medium
include, but are not limited to, optical storage media such as
CD-ROMs and DVDs; magneto-optical storage media, such as MOs;
magnetism storage media, including but not limited to floppy disks
(trademark), cassette tapes, and removable hard disks; media with a
built-in rewriteable non-volatile memory, including but not limited
to memory cards; and media with a built-in ROM, including but not
limited to ROM cassettes; etc. Furthermore, various information
regarding stored images, for example, property information, may be
stored in any other form, or it may be provided in other ways.
Example embodiments being thus described, it will be obvious that
the same may be varied in many ways. Such variations are not to be
regarded as a departure from the spirit and scope of the present
invention, and all such modifications as would be obvious to one
skilled in the art are intended to be included within the scope of
the following claims.
* * * * *