U.S. patent application number 09/453421 was filed with the patent office on 2002-04-18 for magnetic resonance imaging system with an interventional instrument.
Invention is credited to VAN VAALS, JOHANNES J..
Application Number | 20020045815 09/453421 |
Document ID | / |
Family ID | 8234429 |
Filed Date | 2002-04-18 |
United States Patent
Application |
20020045815 |
Kind Code |
A1 |
VAN VAALS, JOHANNES J. |
April 18, 2002 |
MAGNETIC RESONANCE IMAGING SYSTEM WITH AN INTERVENTIONAL
INSTRUMENT
Abstract
A magnetic resonance imaging (MRI) system is provided with an
interventional instrument with an indicator element (5) which
influences, for example locally disturbs, the magnetic resonance
image. The position of the interventional instrument within the
patient to be examined is derived from the local disturbances in
the image as caused by the interventional instrument. The degree of
influencing of the magnetic resonance image is adjustable notably
by rotation of the interventional instrument with the indicator
element relative to the direction of the steady magnetic field of
the magnetic resonance imaging system. For example, the indicator
element is a paramagnetic strip which may include several segments
of different magnetic susceptibility.
Inventors: |
VAN VAALS, JOHANNES J.;
(EINDHOVEN, NL) |
Correspondence
Address: |
US PHILIPS CORPORATION
580 WHITE PLAINS ROAD
TARRYTOWN
NY
10591
|
Family ID: |
8234429 |
Appl. No.: |
09/453421 |
Filed: |
December 2, 1999 |
Current U.S.
Class: |
600/411 ;
600/420 |
Current CPC
Class: |
G01R 33/285 20130101;
G01R 33/281 20130101 |
Class at
Publication: |
600/411 ;
600/420 |
International
Class: |
A61B 005/055 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 3, 1998 |
EP |
98204105.5 |
Claims
1. A magnetic resonance imaging system which includes an
interventional instrument (1) which is provided with an indicator
element (5) for influencing a magnetic resonance image,
characterized in that the degree of influencing of the magnetic
resonance image is adjustable.
2. A magnetic resonance imaging system as claimed in claim 1,
provided with a main magnet system (10) for applying a steady
magnetic field, characterized in that the degree of influencing of
the magnetic resonance image can be adjusted on the basis of the
orientation of the indicator element (5) relative to the steady
magnetic field.
3. A magnetic resonance imaging system as claimed in claim 2, in
which the interventional instrument is provided with a holder,
characterized in that the magnetic susceptibility of the indicator
element significantly deviates from the magnetic susceptibility of
the holder.
4. A magnetic resonance imaging system as claimed in claim 1,
characterized in that the indicator element includes a plurality of
segments, individual segments causing a different degree of
influencing of the magnetic resonance image.
5. A magnetic resonance imaging system as claimed in claim 4,
characterized in that individual segments have a different magnetic
susceptibility.
6. A magnetic resonance imaging system as claimed in claim 2 or 4,
characterized in that the indicator element includes one or more
strips which are arranged so as to extend transversely of the
longitudinal axis of the holder.
7. An interventional instrument intended to co-operate with a
magnetic resonance imaging system and including an indicator
element for influencing a magnetic resonance image, characterized
in that the degree of influencing of the magnetic resonance image
is adjustable.
8. An interventional instrument as claimed in claim 7, the magnetic
resonance imaging system being provided with a main magnet system
(10) for applying a steady magnetic field, characterized in that
the degree of influencing of the magnetic resonance image can be
adjusted on the basis of the orientation of the indicator element
(5) relative to the steady magnetic field.
9. A magnetic resonance imaging system arranged to perform a first
type of magnetic resonance imaging sequence to generate magnetic
resonance signals mainly relating to an interventional instrument
which is introduced in an object to be examined and to perform a
second type of magnetic resonance imaging sequence to generate
magnetic resonance signals mainly relating to said body to be
examined.
Description
[0001] The invention relates to a magnetic resonance imaging system
which includes:
[0002] an interventional instrument which is provided with
[0003] an indicator element for influencing a magnetic resonance
image.
[0004] The invention also relates to an interventional instrument
which is intended to co-operate with a magnetic resonance imaging
system and is provided with an indicator element for influencing a
magnetic resonance image.
[0005] A magnetic resonance imaging system of this kind is used
notably for a medical interventional procedure during which the
interventional instrument is introduced into the body of the
patient to be examined. During the introduction of the
interventional instrument one or more magnetic resonance images are
made of the patient to be examined. Because the indicator element
influences the magnetic resonance image, the position of the
interventional instrument can be picked up and the instantaneous
position of the interventional instrument can also be reproduced in
a rendition of the magnetic resonance image. The indicator element
preferably induces a local disturbance in the magnetic resonance
image. On the basis of the magnetic resonance images the
interventional instrument can thus be tracked inside the body, even
though it is obscured from direct view.
[0006] An interventional instrument of this kind is known from U.S.
Pat. No. 5,728,079. The cited patent also mentions a magnetic
resonance imaging system provided with such an interventional
instrument.
[0007] The known interventional instrument is a catheter provided
with a hollow tubular holder and the indicator element is a
concentric layer of a paramagnetic material. The concentric
paramagnetic layer is provided in the form of a cylindrical sheath
whose longitudinal axis is coincident with the longitudinal axis of
the holder. The paramagnetic material influences the magnetic
resonance image of a patient to be examined by means of the
magnetic resonance imaging system. The influencing of the magnetic
resonance image makes it possible to derive the position of the
interventional instrument within the body of the patient without
the instrument being directly visible. The influencing of the
magnetic resonance image by the paramagnetic layer has an adverse
effect on the diagnostic quality of the magnetic resonance image.
Due to the influencing by the indicator element, notably anatomical
details in the vicinity of the position of the interventional
instrument are reproduced in a disturbed manner.
[0008] It is an object of the invention to provide a magnetic
resonance imaging system with an interventional instrument in which
the position of the interventional instrument within the body of
the patient to be examined can be more accurately derived by
influencing the magnetic resonance image and/or in which the
magnetic resonance image is disturbed less than by the known
interventional instrument. It is notably an object of the invention
to provide a magnetic resonance imaging system with an
interventional instrument whereby the position of the
interventional instrument can be accurately derived without
seriously affecting the diagnostic quality of the magnetic
resonance image.
[0009] This object is achieved by means of a magnetic resonance
imaging system according to the invention which is characterized in
that the degree of influencing of the magnetic resonance image is
adjustable.
[0010] The magnetic resonance imaging system according to the
invention is particularly suitable for use during an intervention.
During an intervention the interventional instrument, for example,
a catheter, is introduced into the body of the patient and magnetic
resonance images of the body of the patient to be examined are then
formed, the interventional instrument being reproduced therein. The
influencing of the magnetic resonance image represents the position
of the interventional instrument; this enables the position of the
interventional instrument to be derived from the influencing of the
magnetic resonance image. Notably, the small region in the magnetic
resonance image which is influenced corresponds with the position
of the interventinal instrument.
[0011] Because the influencing of the magnetic resonance images by
the interventional instrument is adjustable, on the one hand the
magnetic resonance images can be strongly influenced so that the
position of the interventional instrument can be clearly observed
in the magnetic resonance images. On the other hand, through very
weak influencing of the magnetic resonance images by the
interventional instrument it can be ensured that the diagnostic
quality of the magnetic resonance images is hardly degraded by the
interventional instrument. In the case of very weak influencing,
the magnetic resonance image accurately reproduces the anatomy of
the patient to be examined. As a result, the position of the
interventional instrument within the body of the patient can be
accurately derived. For example, magnetic resonance images are
formed during the introduction of the interventional instrument,
the interventional instrument then influencing the magnetic
resonance images to a substantial degree so that the interventional
instrument can be readily tracked in the magnetic resonance images.
As a result, the interventional instrument is clearly reproduced in
the magnetic resonance image so that the interventional instrument
can be tracked within the body of the patient without being
directly visible. The interventional instrument can thus be safely
guided through the body of the patient without unnecessary damaging
of tissue. Once the interventional instrument has been guided to
the desired position, the degree of influencing of the magnetic
resonance images is reduced as much as possible. Magnetic resonance
images in which hardly any disturbances occur can then be formed of
the body of the patient. Such magnetic resonance images have a high
diagnostic quality because they reproduce the anatomy of the
patient to be examined with many details and exactly. When
subsequently the interventional instrument is moved again, the
degree of influencing of the magnetic resonance images by the
interventional instrument is adjusted to a higher value again, so
that the interventional instrument can be suitably tracked in the
magnetic resonance images. The degree of influencing of the
magnetic resonance images can notably be adjusted in such a manner
that anatomical details are reproduced in the magnetic resonance
image with only few disturbances, the disturbance nevertheless
being sufficient for accurate determination of the position of the
interventional instrument.
[0012] These and other aspects of the invention will be described
in detail on the basis of the following embodiments which are
defined in the dependent claims.
[0013] The indicator element causes the influencing of the magnetic
resonance image. Such influencing is produced by the magnetic
properties of the indicator element. Specifically, the magnetic
susceptibility of the indicator element deviates essentially or
even considerably from the magnetic susceptibility of other parts,
such as the holder, of the interventional instrument. Furthermore,
the magnetic susceptibility of the indicator element preferably
deviates significantly from the magnetic susceptibility of the
tissue in the vicinity of the indicator element. It is thus
achieved that the indicator element can induce a distinct
disturbance in the magnetic resonance image, so that the indicator
element can be clearly reproduced in relation to the anatomical
structures in the magnetic resonance image. Preferably, the degree
of influencing of the magnetic resonance image by the
interventional instrument is adjustable by adjustment of the
orientation of the indicator element relative to the steady
magnetic field of the magnetic resonance imaging system. Generally
speaking, the orientation of the indicator element can be readily
controlled without influencing the interventional functions of the
interventional instrument. This is because the interventional
instrument is usually shaped as an elongate holder which can be
rotated about its longitudinal axis within the body within the body
of the patient to be examined. When the holder is rotated about its
longitudinal axis, the indicator element is also rotated relative
to the steady magnetic field. Evidently, it is also possible to
construct the interventional instrument in such a manner that the
indicator element can be rotated, inside the holder, relative to
the steady magnetic field, without the holder being rotated. The
interventional instrument is then moved within the body of the
patient while the elongate holder has an orientation relative to
the steady magnetic field such that considerable influencing of the
magnetic resonance images occurs. Attractive results are achieved
notably when the longitudinal axis of the holder encloses a
significant angle relative to the direction of the steady magnetic
field. In the vast majority of interventional procedures the
interventional instrument is indeed used in such a manner that the
longitudinal axis of the instrument is not directed parallel to the
direction of the steady magnetic field.
[0014] With the exception of the indicator element of the
interventional instrument, the components, such as the holder,
preferably have a magnetic susceptibility which does not influence
or only hardly influences the magnetic resonance image, whereas the
indicator element has a magnetic susceptibility which is capable of
strongly influencing the magnetic resonance image. It has been
found that the interventional instrument can be clearly and
accurately tracked in the magnetic resonance images when use is
made of such an indicator element.
[0015] The indicator element is constructed, for example as a strip
which extends in a direction transversely of the longitudinal axis
of the holder. By rotation of the interventional instrument about
the longitudinal axis it is achieved that the strip is oriented
parallel to the steady magnetic field or transversely of
(preferably perpendicularly to) the steady magnetic field. When the
strip extends parallel to the steady magnetic field, it causes
hardly any or no influencing of the magnetic resonance image. When
the strip extends more or less transversely of the steady magnetic
field, it causes a given influencing of the magnetic resonance
image. The influencing is dependent on the angle enclosed by the
strip relative to the steady magnetic field. Influencing is maximum
when the strip extends perpendicularly to the steady magnetic
field. The indicator element may alternatively include a plurality
of paramagnetic strips, said strips being arranged in such a manner
that, when the interventional instrument is used during operation
of the magnetic resonance imaging system, the strips are
non-rotationally symmetrically arranged relative to the steady
magnetic field.
[0016] The indicator element preferably includes a number of
segments of different magnetic susceptibility. For example, the
indicator element includes strips with segments in the form of
parts of the strip of different materials with a different magnetic
susceptibility. In another embodiment the segments are formed by
separate parts of the strip whose respective dimensions differ in
the direction transversely of the axis of the holder. The indicator
element with a plurality of segments of different susceptibility
causes a plurality of disturbances in the magnetic resonance image;
these disturbances occur at distances from one another which
correspond to the distances between the individual segments.
Preferably, the separate segments of the indicator element are
arranged at regular distances from one another. It is thus achieved
that the respective segments cause disturbances in the magnetic
resonance image which occur at regular distances from one another
therein. A regular pattern of this kind, for example a row of
disturbances at mutually equal distances, can be used as a distance
scale in the magnetic resonance image. Using this distance scale,
the interventional instrument can be readily displaced over a
desired distance within the body of the patient. The interventional
instrument can thus be accurately moved to a desired position while
effectively avoiding unnecessary damaging of tissue.
[0017] A preferred embodiment of a magnetic resonance imaging
system is defined in claim 9. Preferably the magnetic resonance
imaging system is arranged to perform the MR imaging of the
interventional instrument on the one hand and of the body into
which the interventional instrument is introduced on the other hand
on the basis of different magnetic resonance imaging sequences.
Thus it is made possible to optimise both the imaging of the
interventional instrument on the basis of magnetic resonance
signals influenced or generated by the indicator element as well as
the imaging of the tissue of the patient to be examined.
[0018] These and other aspects of the invention are apparent from
and will be elucidated, by way of non-limitative example, with
reference to the embodiments described hereinafter and shown in the
drawing; therein:
[0019] FIG. 1 is a diagrammatic representation of a magnetic
resonance imaging system according to the invention,
[0020] FIG. 2 is a diagrammatic representation in the form of a
partly cut-away side elevation of a first embodiment of the
interventional instrument according to the invention,
[0021] FIG. 3 is a diagrammatic cross-sectional view of the
interventional instrument shown in FIG. 2, and
[0022] FIG. 4 is a diagrammatic representation in the form of a
partly cut-away side elevation of a second embodiment of the
interventional instrument according to the invention.
[0023] FIG. 1 is a diagrammatic representation of a magnetic
resonance imaging system according to the invention. The magnetic
resonance imaging system includes a main magnet 10 which generates
a steady magnetic field in an examination space 11 in which a part
of the patient 30 to be examined is arranged. For example, the main
magnet has a cylindrical bore which is so large that it can
accommodate the relevant part of the patient to be examined. The
steady magnetic field in the bore is essentially spatially uniform.
At the center of the bore a spatial uniformity of the steady
magnetic field is realized such that the relative deviations of the
uniformity do not amount to more than 5.10.sup.-6. The main magnet
is arranged in an examination room which is shielded against RF
electromagnetic fields in order to prevent the operation of the
magnetic resonance imaging system from being disturbed by RF
signals from outside the examination room and by spurious RF
signals generated by the control systems of the magnetic resonance
imaging system itself. The magnetic resonance imaging system also
includes gradient coils 12. The gradient coils 12 generate spatial
gradients in the magnetic field in the examination space.
Furthermore, the magnetic resonance imaging system includes a
transmitter coil 13 and a receiver coil 13. Usually the same coil
or antenna is used alternately as the transmitter coil and the
receiver coil. The transmitter and receiver coil, furthermore, is
usually shaped as a coil but other geometries where the transmitter
and receiver coil acts as a transmitter and receiver antenna for RF
electromagnetic signals are also feasible. The transmitter and
receiver coil 13 is connected to an electronic transmitter/receiver
circuit 15.
[0024] The patient 30 to be examined is arranged on a patient table
14 and moved into the bore of the main magnet in such a manner that
the part of the body of the patient to be examined in the
examination space is situated approximately at the center of the
bore. Using the gradient coils 12, a selection gradient is applied
in order to select a thin slice in the examination space.
Subsequently, the transmitter coil emits an RF electromagnetic
excitation pulse whereby the spins in the body of the patient to be
examined and in the selected slice are excited. The RF
electromagnetic excitation pulse is an FM or AM modulated signal
with a modulation frequency amounting to some tens of MHz. The
excited spins emit RF resonance signals which are received by the
receiver coil 13. A reconstruction unit 25 derives an image signal
(IS), representing an image of a cross-section in the selected
slice of the body of the patient to be examined, from the RF
resonance signals (RFS). For example, the transmitter coil 13
generates one or more refocusing pulses so that the excited spins
have one or more spin echoes where the RF resonance signals are
emitted which are received by the receiver coil. After the
excitation of the spins in the selected slice, the gradient coils
12 apply a phase encoding gradient field, also referred to as a
preparation gradient field, for a predetermined period of time;
this gradient field renders the phase of the precession (the Larmor
precession) of the excited spins location-dependent in a phase
encoding direction in the selected slice. After the emission of the
refocusing pulse, the gradient coils 12 apply a read-out gradient
field, also referred to as a measuring gradient field, whereby the
precessional frequencies (the Larrnor frequencies) of the excited
spins in the selected slice are rendered location-dependent in the
direction of the read-out gradient field. Because of the phase
encoding gradient field and the read-out gradient field, the RF
resonance signals have a plurality of frequency components which
encode the spatial positions in the selected slice. The signal
levels of these frequency components of the RF resonance signals
represent the spin densities in the selected slice and these spin
densities themselves represent the density and the type of tissue
in the selected slice. Using inter alia Fourier analysis of the RF
resonance signals, an image, being the magnetic resonance image, of
a cross-section in the selected slice of the patient to be examined
can thus be reconstructed from the RF resonance signals.
[0025] The gradient coils 12 are energized by means of a power
supply unit 21 whereto the various gradient coils 12 are connected.
The power supply unit 21 is controlled by a front-end controller
20. The function of the front-end controller 20 is carried out, for
example by a suitably programmed electronic processor. Furthermore,
the transmitter and receiver circuit 15 is connected to a modulator
22. The modulator 22 and the transmitter/receiver 15 activate the
transmitter coil 13 so as to transmit the RF excitation and
refocusing pulses. The receiver coil is connected to a
pre-amplifier 23. The pre-amplifier 23 amplifies the RF resonance
signal (RFS) received by the receiver coil and the amplified RF
resonance signal is applied to a demodulator 24. The demodulator 24
demodulates the amplified RF resonance signal. The demodulated
resonance signal contains the actual information concerning the
local spin densities in the selected slice. Using Fourier
transformation and inverse Radon transformation, a reconstruction
unit 25 derives an image signal (IS) which represents the image
information of the spin densities in the selected slice. The image
of the selected slice is displayed on a monitor 26; to this end,
the image signal (IS) is applied to the monitor 26. The image
signal (IS) is also stored in a buffer unit 27 while awaiting
further processing or printing as a hard copy.
[0026] The front-end controller 20 also controls the
transmitter/receiver circuit 15. The pre-amplifier 23 is blocked
during the period of time that the transmitter coil transmits the
excitation pulses or the refocusing pulses; during that period the
transmitter/receiver circuit is tuned by the front-end controller
20 so as to ensure that the pulses transmitted by the transmitter
coils do not damage the transmitter/receiver circuit 15 and the
pre-amplifier 23. The front-end controller 20 tunes the
transmitter/receiver circuit 15 for very sensitive reception of the
RF resonance.
[0027] FIG. 2 is a diagrammatic representation, in the form of a
partly cut-away side elevation, of an interventional instrument
according to the invention. The invention can be used for a solid
interventional instrument as well as a hollow interventional
instrument. Such a hollow interventional instrument includes a
holder 2 in which a cylindrical cavity 3 is recessed so as to
extend along the axis of the holder. The cylindrical cavity 3 is
referred to as the "lumen". The holder terminates as a
needle-shaped tip at a distal end 6. The interventional instrument
1 is thus formed as a hollow needle. Thin cables or rods can be
guided through the lumen; such cables or rods serve for the
electrical or mechanical operation of a surgical instrument which
can be coupled to the distal end of the interventional instrument.
Liquids such as medication, physiological solutions or contrast
agents can also be supplied via the lumen. The interventional
instrument may also be constructed as a biopsy needle for the
removal of pieces of tissue from the body of the patient. The
holder 2 is preferably made from a material having a very low
magnetic susceptibility; for example, the holder 2 is made from
plastic or a ceramic material.
[0028] The interventional instrument 1 is also provided with the
indicator element 5 in the form of two paramagnetic strips 5 which
are provided transversely of the axis of the lumen and in the
vicinity of the distal end of the interventional instrument. The
paramagnetic strips 5 are, for example strips 5 of a plastic
compound such as polyurethane or nylon in which a paramagnetic
material is included. Such a paramagnetic material is, for example
copper, manganese, chromium, nickel or notably gadolinium or
dysprosium. Particularly attractive results are achieved by means
of gadolinium and dysprosium, because these metals have a very high
magnetic susceptibility. For example, a concentration of from 10%
to 30% of the paramagnetic material in the compound is used to
realize a suitable degree of influencing of the magnetic resonance
image by the indicator element. The strips 5 extend in a direction
transversely of the longitudinal axis of the interventional
instrument. Rotation of the interventional instrument about the
longitudinal axis rotates the strips 5 relative to the direction of
the steady magnetic field when the interventional instrument has
been introduced into the patient arranged in the steady magnetic
field. In the example shown in the FIGS. 2 and 3 the indicator
element is constructed in the form of two strips, but it is
alternatively possible to utilize an indicator element comprising
only a single strip or three or more strips.
[0029] The strips 5 as shown in FIG. 2 are notably constructed so
as to have a plurality of segments 51, 52. For example, there are
wide segments 51 and narrow segments 52. The wide segments 51
extend further in the direction transversely of the longitudinal
axis 7 of the interventional instrument than the narrow segments
extending transversely of the longitudinal axis 7. It is thus
achieved that when the interventional instrument with the strips is
arranged in the steady magnetic field of the magnetic resonance
imaging system, the wide segments 51 cause a local distortion of
the steady magnetic field which is stronger than that caused by the
narrow segments 52. The wide segments 51 thus locally influence the
magnetic resonance image more than the narrow segments 51. The
indicator element with strips having a plurality of wide and narrow
segments thus produces a pattern of distortions which can be used
as a distance scale in the magnetic resonance image.
[0030] FIG. 4 is a diagrammatic representation, in the form of a
partly cut-away side elevation, of a second embodiment of the
interventional instrument according to the invention. The indicator
element of the interventional instrument shown in FIG. 4 includes a
plurality of passive segments 53 and a plurality of active segments
54. The active segments are preferably made from a material having
a magnetic susceptibility which deviates significantly from the
magnetic susceptibility of the holder 2; for example, the active
segments are made from a paramagnetic material, for example copper,
manganese, chromium, nickel or notably gadolinium or dysprosium.
The passive elements are made from a material having a very low
magnetic susceptibility, such as plastic or a ceramic material.
* * * * *