Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
2001-02-26
2003-10-28
Robinson, Daniel (Department: 3742)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
Reexamination Certificate
active
06640126
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to magnetic resonance (MR) imaging techniques. In particular, the invention relates to MR imaging that is triggered and/or synchronized with patient sensors that detect physiological conditions, such as a heartbeat, blood pulse, or respiration of the patient being imaged.
BACKGROUND OF THE INVENTION
Magnetic Resonance Imaging (MRI) is a widely accepted and commercially available technique for obtaining digitized visual images representing the internal structure of objects (such as the human body) having substantial populations of atomic nuclei that are susceptible to nuclear magnetic resonance (MR) phenomena. In MRI, nuclei in the body of a patient to be imaged are polarized by imposing a strong main magnetic field (B
0
) on the nuclei. The nuclei are excited by a radio frequency (RF) signal at characteristic MR (Lamor) frequencies. By spatially distributing localized magnetic fields surrounding the body and analyzing the resulting RF responses from the nuclei, a map or image of these nuclei responses as a function of their spatial location is generated and displayed. An image of the nuclei responses provides a non-invasive view of a patient's internal organs and of other tissues.
As shown in
FIG. 1
, an MR imaging system typically includes a magnet
10
to impose the static magnetic field (B
0
), gradient coils
12
for imposing spatially distributed gradient magnetic fields (G
x
, G
y
, and G
z
) having gradients along three respective orthogonal coordinates, and RF coils
14
and
16
to transmit and receive RF signals to and from selected nuclei of the body being imaged. The patient
18
lies on a patient table
20
such that a portion of the patient to be imaged is moved, in three-dimensions, into an “imaging volume” between the magnet and coils, which defines a field of view (FOV) of the MRI system. One or more sensors, such as electrocardiogram (EKG) sensor
21
, may be positioned on the patient to monitor physiological conditions of the patient, such as the heartbeat.
The MRI system operator controls the system through a computer workstation
22
with a keyboard, screen and other operator input/output devices. The MRI system operator positions the patient within the imaging volume using a movable table
20
, and may attach sensors
21
that monitor the patient during imaging.
Sensors
21
monitor the heartbeat, respiration, blood pulse and/or other physiological conditions of the patient. Signals generated by these sensors may be applied by the MRI system to trigger or synchronize MR imaging with the physiological condition(s) being monitored. For example, a heartbeat sensor generates a signal indicative of the patient's heartbeat that is applied to trigger an MR imaging sequence synchronized with the beating heart. Synchronization of an MR image with a beating heart may improve the clarity of an still image of the beating heart or enable a real-time image of the heart. Similarly, sensors monitoring physiological conditions may be used to synchronize MR imaging with respiration, blood pulses, and other conditions of the patient. The signal from the monitor may also be recorded synchronously with the image data and used for post-processing.
Sensors to monitor physiological conditions are well known. For example, EKG electrical sensors mounted on a patient's skin detect electrical signals from the heart and generate signals indicative of the heartbeat. Fluid flow sensors mounted near the nose or mouth of a patient detect a patient's breath and generate a respiration signal. Similarly, electromechanical sensors mounted on the chest or back of a patient detect changes in the shape of the abdomen to generate signals indicative of the respiration of the patient. Blood pulse can be detected by light sensors that detect light reflected from skin or by pressure sensors that detect pressure changes in an inflated bladder wrapped around the patient's arm.
The placement of such sensors on the patient's body can be critical. If the sensor is not placed optimally, then the triggering of MRI scans can be affected. For example, the analog signal generated by the sensor might be of insufficient magnitude to even pass through a detection threshold. Alternatively, the passage through a preset threshold may be incorrectly timed and/or unreliable. Thus, the sensor placement should be checked for correctness before expensive and time consuming actual MRI scans are conducted.
Providing an audio and/or visual signal feedback indicative of proper sensor placement on a patient prior to MR imaging can be difficult. MR imaging is extremely sensitive to stray electromagnetic emissions. Such emissions may be emitted by signal wires and circuits associated with sensors. To reduce interference due to extraneous emissions, wires and circuits within the MRI imaging room and especially near the patient are minimized. In particular, the wires within the MR imaging room are preferably limited to only those wires needed for the gradient coils and the RF coils. Other signal wires and circuits are generally precluded from the MR imaging room.
Conventional CRT oscilloscopes that are often used to provide a visual feedback of patient sensor placement cannot be used in the presence of the strong B
0
magnetic field within an MRI gantry room. In addition, the additional wires and circuits associated with the oscilloscope may, if left in the gantry room, cause unnecessary interference with the MRI process—and thus must typically be located in an inconvenient place outside the gantry room. Similar problems of inconvenience occur if an MRI system monitor outside the gantry room is utilized to monitor sensor placement. Moreover, even if the oscilloscope or MRI system monitor were used, it would add to the cost of the MRI system. Still further, to view an auxiliary monitor, its visual display requires that an operator turn away from the MRI imaging screen to determine whether the sensor is properly placed and functioning. Thus, while in-room monitors have been developed for MRI systems, (See U.S. Pat. No. 5,184,074, issued to Kaufman et al.) they have various disadvantages such as cost, complexity and possible stray RF emissions.
In MRI it is sometimes desirable to trigger or synchronize the image acquisition sequence with a physiologically generated signal, such as the heartbeat, the blood pulse or the respiration. The typical MRI system provides an input where a digital ON-OFF signal is used to create within the machine such triggering or synchronization.
To generate this digital signal, an analog signal is first created by direct monitoring of the physiologic process of interest. Examples are EKG detection for the heartbeat, breath or abdomen shape for breathing, and pressure or reflected light for blood flow. The signal these processes create is continuous, and a trigger level or threshold has to be set to extract from them a desired ON-OFF signal.
The analog detection devices are attached to the body or otherwise interact with it, and because of patient-to-patient variability, operators need to locate them in certain ways, or need to test different locations to get a reliable signal. Thus, the signal needs to be monitored. This is typically done with an oscilloscope or by digitizing the continuous signal and displaying it on the MRI console monitor.
Oscilloscopes themselves need adjustment that is sometimes beyond the capabilities of the MRI operators, they add cost, and they do not work near the MRI magnets. The console display is reliable and simple, but requires that the operator move between the patient and the console, which is in a different room. This adds time to the setup process. An in-room monitor for real time display (U.S. Pat. No. 5,184,074) could be used to display the signal, but it adds cost.
There is a long-felt need for an economic device that provides sensor signal feedback, such as of an EKG heartbeat signal, to an MRI technician within the MRI gantry room. It is desirable that this device not add extra w
Nixon & Vanderhye P.C.
Robinson Daniel
Toshiba America MRI Inc.
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