U.S. patent number 3,871,360 [Application Number 05/383,707] was granted by the patent office on 1975-03-18 for timing biological imaging, measuring, and therapeutic timing systems.
This patent grant is currently assigned to Brattle Instrument Corporation. Invention is credited to Paul Epstein, Patrick G. Phillipps, Joseph M. Van Horn.
United States Patent |
3,871,360 |
Van Horn , et al. |
March 18, 1975 |
Timing biological imaging, measuring, and therapeutic timing
systems
Abstract
System for timing biological imaging, measuring, or therapeutic
apparatus in accordance with selected physiological states of a
subject, featuring in various aspects generation of respiratory
windows on the basis of processed electrical signals derived from
prior respiration history, digital offset correction circuitry for
the respiratory signals, and generation of cardiac timing signals
on the basis of prior cardiac cycle history.
Inventors: |
Van Horn; Joseph M. (Cambridge,
MA), Epstein; Paul (Brookline, MA), Phillipps; Patrick
G. (Newton, MA) |
Assignee: |
Brattle Instrument Corporation
(Cambridge, MA)
|
Family
ID: |
23514339 |
Appl.
No.: |
05/383,707 |
Filed: |
July 30, 1973 |
Current U.S.
Class: |
600/484;
378/95 |
Current CPC
Class: |
G01T
1/1648 (20130101); A61B 5/0809 (20130101); A61B
6/541 (20130101) |
Current International
Class: |
A61B
5/08 (20060101); A61B 6/00 (20060101); G01T
1/164 (20060101); G01T 1/00 (20060101); A61b
005/02 () |
Field of
Search: |
;128/1D,2.6A,2.6B,2.6F,2.6G,2.6R,2.5R,2.08,2.1R,2.1Z,DIG.13,145.
;340/279 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Kamm; William E.
Claims
What is claimed is:
1. A system for timing biological imaging, measuring, or
therapeutic apparatus in accordance with selected respiratory
events in a subject, comprising
respiratory input circuitry means for providing electrical signals
representative of the respiratory cycles of said subject,
respiratory timing circuitry means effectively connected to said
input circuitry means for processing said electrical signals and
for generating a succession of windows surrounding predicted
respiratory events of successive respiratory cycles, including
means for basing the generation of each said window in a given
cycle upon the results of said processing of electrical signals
derived from respiration prior to said given cycle, and
means for effectively connecting said system to said apparatus to
be controlled.
2. The system of claim 1 further comprising
cardiac input circuitry means for providing electrical signals
representative of the cardiac cycles of said subject,
cardiac timing circuitry means effectively connected to said
cardiac input circuitry means for producing a successsion of timing
signals corresponding to selected points in successive cardiac
cycles, and
output circuitry means effectively connected to said respiratory
and cardiac timing circuitry means, and including logic circuitry
means, for producing a succession of output signals corresponding
to successive said timing signals occurring within said
windows.
3. The system of claim 2 wherein said respiratory timing circuitry
includes means for causing the majority of said windows to be of
duration longer than the combined duration of a plurality of
successive said timing signals occurring within the respective said
window, and the interval between said successive signals.
4. The system of claim 2 further comprising recorder means
effectively connected to said cardiac input circuitry means and to
said logic circuitry means, for recording a synchronous display of
said cardiac cycle and the timing of said output signals.
5. The system of claim 4 wherein said recorder means includes means
for including in said synchronous display a record of said
respiratory windows.
6. The system of claim 2 wherein said cardiac timing circuitry
means includes cardiac interval circuitry means effectively
connected to said cardiac input circuitry means for generating a
succession of interval values corresponding to the lengths of
successive cardiac cycles, and timing signal circuitry means
effectively connected to said interval circuitry means for
generating each said timing signal at a time dependent upon a
fraction of the interval value for the next previous cardiac
cycle.
7. The system of claim 6 wherein said timing signal circuitry means
includes means for generating each said timing signal at a time
dependent upon a constant value plus a fraction of the interval
value for the next previous cardiac cycle.
8. The system of claim 6 wherein said interval circuitry means
includes means for generating a succession of interval values
correponding to intervals between QRS complexes of successive
cardiac cycles, and said timing signal circuitry means includes
means for generating each said timing signal at a time subsequent
to the QRS complex for that cardiac cycle equal to a constant value
plus a portion of the interval value for the next previous cardiac
cycle.
9. The system of claim 8 wherein said portion is between 15 and 30%
to cause said timing signal to represent systole.
10. The system of claim 8 wherein said portion is between 75 and
90% to cause said timing signal to represent diastole.
11. The system of claim 6 wherein said timing signal circuitry
means includes means for changing in successive cardiac cycles the
fraction of said interval value upon which the respective timing
signal is based.
12. The system of claim 2 further comprising arrythmia detection
circuitry means effectively connected to said cardiac input
circuitry means and to said logic circuitry means for detecting
cardiac arrythmia by comparison with cardiac cycles expected on the
basis of said cardiac timing signals.
13. The system of claim 1 wherein said respiratory timing circuitry
means includes means for generating values respectively
representative of maximum and minimum expiration within a
respiratory cycle of said subject, and respiratory state definition
circuitry means for generating said windows as a function of both
said values.
14. The system of claim 13 wherein said means for generating values
comprises peak detectors.
15. The system of claim 14, wherein said peak detectors include
means for storing values therein and for causing said stored values
to decay over time.
16. The system of claim 14 wherein said respiratory state
definition circuitry means includes threshold detection circuitry
means effectively connected to said peak detectors and to said
input circuitry means.
17. The system of claim 16 wherein said threshold detection
circuitry means includes means for preventing its output from
changing despite variations in the respiratory signal from said
respiratory input circuitry smaller than a preselected limit.
18. The system of claim 1 further comprising digital offset
correction circuitry means effectively connected to said
respiratory input circuitry means for automatically causing said
electrical signals representative of respiratory cycles to be
within a predetermined range.
19. The system of claim 18 wherein said correction circuitry means
includes limit detection means effectively connected to said
respiratory input circuitry for providing a signal when the
respiratory signal is outside said range, digital means effectively
connected to said detection means for providing digital pulses in
the presence of a signal from said detection means, a counter
effectively connected to said digital means for counting said
pulses, and offset generator means effectively connected to said
respiratory input circuitry means for generating an offset voltage
dependent upon the count in said counter.
20. The system of claim 19 wherein said detection means includes
upper and lower limit detectors for respectively incrementing and
decrementing said counter when the respiratory signal is above and
below said range.
21. The system of claim 19 further comprising means for
periodically automatically changing the count in said counter to
cause said respiratory signal to drift in a predetermined
direction.
22. A system for timing biological imaging, measuring or
therapeutic apparatus in accordance with selected physiological
states of a subject, comprising
cardiac input circuitry means for providing electrical signals
representative of the cardiac cycle of said subject,
cardiac timing circuitry means effectively connected to said
cardiac input circuitry means for producing a succession of timing
signals corresponding to selected predicted cardiac events in
successive cardiac cycles, said timing circuitry means including
interval circuitry means for generating a succession of interval
values corresponding to intervals between QRS complexes of
successive cardiac cycles, and timing signal circuitry means
effectively connected to said interval circuitry means for
generating each said timing signal at a time subsequent to the QRS
complex for that cardiac cycle equal to a time constant related to
the refractory time of the heart muscle minus half the width of
said timing signals plus a fraction of the interval for the next
previous cardiac cycle, to cause each said timing signal to
surround said predicted cardiac event, and
means for effectively connecting said system to said apparatus to
be controlled.
23. The system of claim 22 wherein said portion is between 15 and
30% to cause said timing signal to represent systole.
24. The system of claim 22 wherein said portion is between 75 and
90% to cause said timing signal to represent diastole.
25. The system of claim 22 wherein said timing signal circuitry
means includes means for changing in successive cardiac cycles the
fraction of said interval value upon which the respective timing
signal is based.
26. The system of claim 22 further comprising arrythmia detection
circuitry means effectively connected to said input circuitry means
and to said cardiac timing circuitry means for detecting cardiac
arrythmia by comparison with cardiac cycles expected on the basis
of said cardiac timing signals.
27. The system of claim 22 wherein said time constant is between 50
and 150 milliseconds.
28. A system for timing biological imaging, measuring or
therapeutic apparatus in accordance with selected physiological
states of a subject, comprising
input circuitry means for providing electrical signals
representative of a physiological cycle of said subject,
output circuitry means effectively connected to said input
circuitry means for providing a succession of timing signals at
selected portions of said physiological cycles, and
digital offset correction circuitry means effectively connected to
said input circuitry means for automatically causing said
electrical signals representative of physiological cycles to be
within a predetermined range, said correction circuitry means
including limit detection means effectively connected to said input
circuitry for providing a signal when the physiological signal is
outside said range, digital means effectively connected to said
detection means for providing digital pulses in the presence of a
signal from said detection means, a counter effectively connected
to said digital means for counting said pulses, said detection
means including upper and lower limit detectors for respectively
incrementing and decrementing said counter when the physiological
signal is above and below said range, and offset generator means
effectively connected to said input circuitry means for generating
an offset voltage dependent upon the count in said counter, and
means for effectively connecting said system to said apparatus to
be controlled.
29. A system for timing biological imaging, measuring or
therapeutic apparatus in accordance with selected physiological
states of a subject, comprising
input circuitry means for providing electrical signals
representative of a physiological cycle of said subject,
output circuitry means effectively connected to said input
circuitry means for providing a succession of timing signals at
selected portions of said physiological cycles, and
digital offset correction circuitry means effectively connected to
said input circuitry means for automatically causing said
electrical signals representative of physiological cycles to be
within a predetermined range, said correction circuitry means
including limit detection means effectively connected to said input
circuitry for providing a signal when the physiological signal is
outside said range, digital means effectively connected to said
detection means for providing digital pulses in the presence of a
signal from said detection means, a counter effectively connected
to said digital means for counting said pulses, offset generator
means effectively connected to said input circuitry means for
generating an offset voltage dependent upon the count in said
counter, and means for periodically automatically changing the
count in said counter to cause said physiological signal to drift
in a predetermined direction, and
means for effectively connecting said system to said apparatus to
be controlled.
Description
BACKGROUND OF THE INVENTION
This invention relates to timing biological imaging, measuring, or
therapeutic systems (in the broad sense, including, e.g., an X-ray
machine or a nuclear camera) in accordance with the respiratory and
cardiac states of the body.
Monitoring the respiratory state by detecting the variations in
electrical impedance produced during the breathing cycle is
described in Geddes et al., "The Impedance Pneumograph," Aerospace
Medicine, January, 1962, pages 28-33. Timing an X-ray machine in
accordance with respiratory state (e.g., to obtain an X-ray image
when the lungs are fully inflated) is described in Robertson U.S.
Pat. No. 3,524,058. Timing an X-ray machine in accordance with the
cardiac cycle is described in Becker U.S. Pat. No. 3,626,932, where
the use of a pulmonary synchronization unit is also mentioned.
X-ray timing based upon a percentage of heart beat interval is
described in Strauss et al. U.S. Pat. No. 2,190,389.
Accurate timing is important for many reasons, including for
obtaining images or measurements that are not blurred by heart or
lung motion, and for making possible precise and reproduceable
comparisons of images or measurements taken at different
physiological states.
SUMMARY OF THE INVENTION
The invention provides highly refined monitoring of the respiratory
and cardiac cycles, and makes possible very accurate and automatic
timing to a selected physiological state, with equipment that is
reliable, easily operated by an unskilled technician, and not
unduly costly or complex. Timing accuracy is achieved, with respect
to the respiratory state, despite impedance variations over time
and from patient to patient that far exceed variations within a
breathing cycle, and, with respect to cardiac state, despite normal
beat to beat rate variations.
In general the invention features, in one aspect, input circuitry
for providing electrical signals representative of the respiratory
cycles of the subject, and respiratory timing circuitry for
processing the electrical signals and for generating a succession
of windows corresponding to selected portions of successive
respiratory cycles, including means for basing the generation of
each window in a given cycle upon the results of the processing of
electrical signals derived from respiration prior to the given
cycle. In another aspect the invention features input circuitry for
providing electrical signals representative of the cardiac cycle of
the subject, and cardiac timing circuitry for producing a
succession of timing signals corresponding to selected points in
successive cardiac cycles, the timing circuitry including interval
circuitry for generating a succession of interval values
corresponding to the lengths of successive cardiac cycles, and
timing signal circuitry for generating each cardiac timing signal
at a time dependent upon a constant value plus a fraction of the
interval for the next previous cardiac cycle. In yet another aspect
the invention features digital offset correction circuitry for
automatically causing electrical signals respresentative of
respiratory cycles to be within a predetermined range, including
limit detection circuitry for providing a signal when the
respiratory signal is outside the range, digital means for
providing pulses in the presence of a signal from the detection
circuitry, a counter for counting the pulses, and an offset
generator for generating an offset voltage dependent upon the count
in the counter. In preferred embodiments a majority of the
respiratory windows are of duration sufficient to span a plurality
of the cardiac timing signals; the respiratory timing circuitry
includes means for generating values respectively representative of
maximum and minimum expiration within a respiratory cycle, and
respiratory state definition circuitry for generating the windows
in a manner dependent upon both those values; a recorder provides a
synchronous display of cardiac cycle, respiratory state, and the
timing of the output control signals; the input cicuitry generates
digital pulses corresponding to occurrences of QRS complexes, and
the cardiac timing circuitry generates cardiac timing signals each
at a time subsequent to the QRS complex equal to a constant value
plus a fraction of the interval value for the next previous cardiac
cycle, the constant value being a timing constant related to the
refractory time of the heart muscle minus half the width of the
cardiac timing pulses; the timing signal circuitry includes means
for changing in successive cardiac cycles the fraction of the
interval value upon which the respective timing signal is based;
arrythmia detection circuitry is provided for detecting cardiac
arrythmia by comparison with cardiac cycles expected on the basis
of the cardiac timing signals; and the offset correction circuitry
includes upper and lower limit detectors for respectively
incrementing an decrementing the counter when the respiratory
signal is above and below th range, and means for periodically
automatically changing the count in the counter to cause the
respiratory signal to drift in a predetermined direction.
Other advantages and features of the invention will be apparent
from the description and drawings herein of a preferred embodiment
thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates the use of a synchronizer embodying the
invention to time a nuclear camera;
FIGS. 2-4 are block diagrams showing the details of the
synchronizer of FIG. 1; and
FIG. 5 illustrates typical waveforms associated with the patient
and the synchronizer.
DESCRIPTION OF THE PREFERRED EMBODIMENT
FIG. 1 shows the synchronizer of the invention in a system
including a nuclear camera 10. The synchronizer 12 detects
respiratory and cardiac signals through silver-silver chloride ECG
electrodes 14 attached midline to the patient's fifth or sixth
intercostal space and controls logic 16 to gate signals from
radiation detector 18 to CRT display 20 whenever systole occurs
during expiration in the respiratory cycle. Successive signals are
integrated in the display, and the integration over a period of
time is photographed by the camera.
Referring to FIGS. 2 - 4, electrodes 14 are connected to impedance
plethysmograph 30, which passes a small (e.g., 100 KHz) current
through the electrodes and detects the change in the patient's
transthoracic impedance, which is proportional to respiration. The
output of the plethysmograph, an analog voltage proportional to
respiration, is fed to a positive peak voltage detector 32, a
negative peak voltage detector 34, and a digital offset correction
circuit 36.
Circuitry 36 consists of two analog comparators 38 and 40 which
function as preset high and low voltage limit detectors. The limit
detectors drive a binary up-down counter 42 which in turn drives a
digital to analog converter 44. The output of converter 44 goes to
the plethysmograph as an offset correction signal which is added to
the plethysmograph output to bring the output into the desired
operating range, which is chosen to be sufficiently wide to
accommodate signal excursion within the respiration cycle. More
particularly, if the output voltage of the plethysmograph is above
the desired operating range, detector 38 gates pulses into the up
count input 46 of counter 42. As the counter counts up, the output
of converter 44, a negative voltage proportional in magnitude to
the value in the counter, goes more negative. The increasing offset
eventually brings the output of the plethysmograph below the
threshold of the high voltage limit detector. If the output of the
plethysmograph is below the desired operating range, detector 40
gates pulses into the down count input 48 of the counter. The
offset correction signal from converter 44 becomes less negative
and again the plethysmograph output is brought into the desired
range. Periodically (e.g., every 15 seconds) counter 42 is
incremented by clock 49 one bit to produce a slow downward drift of
the base line signal. If the signal crosses the lower limit of the
desired range detector 40 is activated and gates a single pulse to
the down count input 48 to restore the counter to its former state.
In this way the digital circuitry allows the plethysmograph to pass
the slowly varying respiratory signal yet respond quickly when the
signal is out of range, and eliminates the need for the operator to
make an otherwise critical and frequent adjustment, since impedance
variations over time and from patient to patient far exceed the
variations within a respiratory cycle.
Detectors 32 and 34 respectively detect and store the most positive
and most negative recent excursions of the respiratory signal, and
decay over time to track signals which become smaller or vary in
their voltage excursions. Weighted fractions of the peak positive
and negative signals are sent respectively to the positive and
negative threshold detect circuits 50 and 52, which also receive
the analog respiratory signal directly from the plethysmograph. If
the analog respiratory signal exceeds 0.8 times the positive peak
voltage plus 0.2 times the negative peak voltage the patient is
defined as being in expiration. If the analog signal is less than
0.8 times the negative peak voltage plus 0.2 times the positive
peak voltage, the patient is defined as being in inspiration. The
threshold detect circuits thus generate windows 54, 56 (FIG. 5),
based upon previous respiratory peaks, which respectively span
generally flat zones surrounding the points of peak inspiration and
respiration in the respiratory cycle. Ten percent hysteresis in the
threshold detect circuits prevents the outputs from changing state
if the analog respiratory signal has small voltage deviations due
to irregular respiration or patient motion. For example, the analog
respiratory signal has to drop to 0.7 times the positive peak
voltage plus 0.2 times the negative peak voltage to turn off the
positive threshold detect signal. Similarly, the signal has to
exceed 0.7 times the negative peak voltage plus 0.2 times the
positive peak voltage to turn off the negative threshold detect
once it has been activated. The hysteresis also forces the
threshold circuits to generate symmetrical output pulses with
respect to time for a symmetrical input signal. The impedance
plethysmograph and associated peak detectors and threshold
detectors have a dynamic operating range of signal of greater than
40 to 1.
The patient's electrocardiogram is picked up from electrodes 14 and
amplified by a low noise, high input impedance preamplifier stage
60 and passed through an isolation amplifier 62. The signal is
coupled optically through amplifier 62 to provide patient safety.
No direct electrical path exists between the patient electrodes and
the machine. Power for preamplifier 60 and amplifier 62 is provided
by an isolated power supply 64 which has no direct electrical
connection to the machine. The impedance plethysmograph 30 is
similarly decoupled from the patient.
From amplifier 62 the ECG signal is passed through a 60 Hz notch
filter 66 to remove any power line noises, and then to recorder
drive and control circuits 68 and to 17 Hz bandpass filter 70. The
bandpass filter approximates a matched filter for the normal adult
QRS complex of the electrocardiogram, that is, it allows only those
signals to pass which have a frequency distribution similar to the
frequency content of the QRS complex of an electrocardiogram.
The bandpass filtered signal then goes to precision full wave
rectifier 72, which takes the absolute value of the incoming signal
(i.e., it allows positive signals to pass unmodified and reverses
the polarity of negative signals) so that the output of the circuit
is always positive.
The rectified signal goes to a peak voltage detector 74 and, along
with the output of detector 74, to a threshold comparator 76.
Detector 74 tracks and stores the most positive recent excursion of
the signal, decaying in time to track signal magnitudes varying
with time. Comparator 76 generates an output pulse if the rectified
signal exceeds 0.8 times the peak detect voltage. The pulse from
the comparator triggers a one-shot 78, which puts out a uniform
width, single pulse for each detected QRS complex.
Ramp generator 80 repeatedly produces a linearly rising voltage.
The detection of a QRS complex in the electrocardiogram causes the
sample and hold circuit 82 to store the instantaneous voltage of
the ramp generator, a value proportional to the last QRS to QRS
interval, and resets generator 80 to zero to start a new ramp.
Threshold detectors 84 and 86 each receive as inputs both the
instantaneous ramp voltage from generator 80 and the output of
circuit 82. Detectors 84 and 86 each include circuitry for
comparing the instantaneous ramp voltage with a function of the
output of circuit 82 (i.e., the previous QRS to QRS interval). In
the embodiment shown detector 84 is designed to trigger one-shot 88
when the instantaneous ramp voltage equals a constant voltage Vo
plus 20% of the output of circuit 82 (corresponding to 20% of the
previous QRS to QRS interval), closely approximating the occurrence
of the systole. Similarly, detector 86 is designed to trigger
one-shot 90 when the innstantaneous ramp voltage equals Vo plus 80%
of the output of circuit 82, closely approximating the occurrence
of diastole. In general, such detectors can be arranged to trigger
a one-shot at any desired point in the cardiac cycle. In
particular, useful embodiments include detectors arranged to
trigger a one-shot at different points in successive cardiac
cycles, e.g., to provide a set of images of the heart at different
points in the cycle. Such a possible threshold detector 87 for
variable timing, with associated one-shot 89, is shown in dashed
lines in FIG. 3. In the embodiment shown Vo represents a time
interval of 100 milliseconds, which has been discovered to
correspond to the refractory time for the heart muscle, minus half
the width of the one-shot pulse. The refractory constant of 100
milliseconds can be varied within a preferred range of 50-150
milliseconds, as 20% and 80% fractions of QRS interval for systole
and diastole correspondingly vary within respective preferred
ranges of 15-30% and 75-90%.
The signals defining the respiratory windows and the cardiac timing
signals are routed to gating and control logic 100, along with
signals from the front panel controls and indicators 102. The
physiological states selected by the operator are sent to the
interface circuits 104 to time the device connected to the
synchronizer in accordance with the selected states. For example,
an imaging device may be timed for exposure whenever systole occurs
in a respiratory window.
A majority of the respiratory windows are wide enough to encompass
a plurality of cardiac timing signals.
Arrythmia detect logic 106 detects the presence of an arrythmia
occurring during cardiac gated exposure as defined in the two
following ways. If a QRS complex is detected during a systole gated
exposure, it is defined as an arrythmia. If no QRS complex is
detected within 300 milliseconds after a diastole gated exposure
occurs, it is defined as an arrythmia. The percent arrythmic beats
computer 108 counts the number of arrythmias occurring and displays
the percentage of arrythmic beats that have occurred after 100, 200
and 400 gated cardiac exposures. The display is in true percent
shown on a numeric display 110.
The recorder control and drive electronics 68 receives the
respiratory window and cardiac timing signals as well as the
electrocardiographic signal from filter 66 and processes these
signals for the strip chart recorder 112. The strip chart recorder
prints out an electrocardiogram and two event marks. One event mark
places a line on the chart when a selected respiratory state is
occurring. The other event mark puts a line on the chart whenever
the conditions for exposure are met. The event marks are placed on
the chart synchronously with the electrocardiogram and allow the
operator to observe that exposures are being made at the proper
time in the cardiac cycle. In the case of an X-ray exposure, the
ECG is marked by the event marker to show the exact time of the
specific cardiac cycle during which the exposure was made.
Other embodiments are within the following claims.
* * * * *