Patent Application
20070249930
The features and advantages of the present invention will become apparent from the following detailed description of the invention when read with the accompanying drawings in which:
The operation of the MR system is controlled from an operator console 100 which includes a keyboard and control panel 102 and a display 104. The console 100 communicates through a link 116 with a separate computer system 107 that enables an operator to control the production and display of images on the screen 104. The computer system 107 includes a number of modules which communicate with each other through a backplane. These include an image processor module 106, a CPU module 108, and a memory module 113, known in the art as a frame buffer for storing image data arrays. The computer system 107 is linked to a disk storage 111 and a tape drive 112 for storage of image data and programs, and it communicates with a separate system control 122 through a high speed serial link 115.
The system control 122 includes a set of modules connected together by a backplane. These include a CPU module 119 and a pulse generator module 121 that connects to the operator console 100 through a serial link 125. It is through this link 125 that the system control 122 receives commands from the operator that indicates the scan sequence that is to be performed. The pulse generator module 121 operates the system components to carry out the desired scan sequence. It produces data that indicate the timing, strength, and shape of the radio frequency (RF) pulses which are to be produced, and the timing of and length of the data acquisition window. The pulse generator module 121 connects to a set of gradient amplifiers 127, to indicate the timing and shape of the gradient pulses to be produced during the scan. The pulse generator module 121 also receives subject data from a physiological acquisition controller 129 that receives signals from a number of different sensors connected to the subject 200, such as ECG signals from electrodes or respiratory signals from a bellows. And finally, the pulse generator module 121 connects to a scan room interface circuit 133 that receives signals from various sensors associated with the condition of the subject 200 and the magnet system. It is also through the scan room interface circuit 133 that a positioning device 134 receives commands to move the subject 200 to the desired position for the scan.
The gradient waveforms produced by the pulse generator module 121 are applied to a gradient amplifier system 127 comprised of Gx, Gy and Gz amplifiers. Each gradient amplifier excites a corresponding gradient coil in an assembly generally designated 139 to produce the magnetic field gradients used for position encoding acquired signals. The gradient coil assembly 139 forms part of a magnet assembly 141 which includes a polarizing magnet 140 and a RF coil system 152. Volume 142 is shown as the area within magnet assembly 141 for receiving subject 200 and includes a patient bore. As used herein, the usable volume of a MRI scanner is defined generally as the volume within volume 142 that is a contiguous area inside the patient bore where homogeneity of main, gradient and RF fields are within known, acceptable ranges for imaging. A transceiver module 150 in the system control 122 produces pulses that are amplified by a RF amplifier system 151 and coupled to the RF coil system 152 by a transmit/receive switch system 154. The resulting signals radiated by the excited nuclei in the subject 200 may be sensed by the same RF coil system 152 and coupled through the transmit/receive switch system 154 to a preamplifier system 153. The amplified MR signals are demodulated, filtered, and digitized in the receiver section of the transceiver 150. The transmit/receive switch 154 is controlled by a signal from the pulse generator module 121 to electrically connect the RF amplifier system 151 to the RF coil system 152 during the transmit mode (i.e., during excitation) and to connect the preamplifier system 153 during the receive mode. The transmit/receive switch system 154 also enables a separate RF coil, for example, a head coil or surface coil to be used in either the transmit or receive mode. In embodiments of the present invention, embodiments of the separate RF coil will be described with reference to
The MR signals picked up by the RF coil system 152 or a separate receive coil (not shown, for example, a body, head, extremity or surface coil) are digitized by the transceiver module 150 and transferred to a memory module 160 in the system control 122. When the scan is completed and an entire array of data has been acquired in the memory module 160, an array processor 161 operates to Fourier transform the data into an array of image data. These image data are conveyed through the serial link 115 to the computer system 107 where they are stored in the disk memory 111. In response to commands received from the operator console 100, these image data may be archived on the tape drive 112, or they may be further processed by the image processor 106 and conveyed to the operator console 100 and presented on the display 104. Further processing is performed by the image processor 106 that includes reconstructing acquired MR image data. It is to be appreciated that a MRI scanner is designed to accomplish field homogeneity with given scanner requirements of openness, speed and cost.
In embodiments of the present invention, MR imaging is performed during an interventional procedure on subject 200 of
In accordance with embodiments of the present invention, a method for acquiring images of an interventional device 210 and its surroundings during MRI is provided. The method for acquiring images during an interventional procedure using a Magnetic Resonance Imaging (MRI) device comprises acquiring at least one planar image of a region of interest and acquiring at least one image of an interventional device projected onto the planar image substantially simultaneously. The method further comprises controlling at least one RF transmit channel in the MRI device in order to produce projection images of the interventional device during an imaging session.
In this embodiment, the method enables simultaneously achieving planar (e.g. two-dimension or 2D) imaging of the subject at any prescribed scan plane and projection imaging of a device/its surroundings, even in cases where the device is located entirely outside the prescribed scan plane. Key components of the method include integration of auxiliary transmit coils with the tracked device, control of the coils' RF transmission through additional RF transmit channels that operate in parallel with a scanner's principal RF transmit channel, and producing projection images in rapid succession.
In order to have a MRI method that enables simultaneous planar roadmap imaging and device tracking according to embodiments of the present invention, the MRI system of
For monitoring the placement of a catheter during an interventional procedure, a parallel RF transmit-based MRI imaging sequence through pulse generator 121 of
The method is applicable on an MR scanner that is equipped with multiple parallel RF transmit channels. The method involves integrating auxiliary RF transmit and/or receive coils with the tracked device(s), controlling the transmit and receive function of both the scanner's standard RF coil(s) and the auxiliary RF coils, and producing projection images in rapid succession.
In one embodiment, the MR imaging system of
In a further embodiment, the auxiliary coils are also configured to receive MR signal. The data collected by the auxiliary coils are processed and combined with the data from the standard receive coil(s) to achieve contrast enhancement of the projection 2D images.
The integration of auxiliary transmit coils with a tracked device can be done in many ways. To track a catheter for instance, one can attach small transmit coils, with or without water-filled vials, to a segment of the catheter at a set of selected locations, as shown in
In a further exemplary embodiment, a two-channel implementation is now described—while the MR scanner's principal RF transmit channel drives a regular or designated transmit coil (e.g., an originally installed whole-body birdcage coil) to accomplish slice selection, the second channel may drive an auxiliary transmit coil with a non-selective or mildly-selective narrow pulse that is played-out at a time instant chosen for obtaining proper gradient refocusing (see
As part of the first embodiment, one can design the auxiliary coil(s) to change device-slice contrast and/or adjust the level of RF inputs to all transmit coils to alter device-slice contrast on the fly.
With this embodiment, superposition of device location information onto the roadmap planar image is automatically accomplished. And most significantly, the creation of such a “tracking+roadmap” image can be repeated as fast as regular planar roadmap imaging—acquiring and presenting tracking information does not incur speed penalty. With appropriate on-the-fly prescription of slice location, this facilitates high frame-rate visualization of both subject anatomy and device position.
Simultaneous roadmap imaging and device tracking were evaluated with the support of an 8-channel parallel transmit-capable MRI scanner and an adapted gradient echo sequence that accommodates the parallel excitation pulses shown in
In terms of pulse sequence timing, parallel transmission of a narrow pulse on the second channel incurs no speed penalty. This implies fully retained freedom in optimizing the gradient echo sequence and good portability of the scheme to other rapid planar imaging sequences of choice.
In a further embodiment, the auxiliary coils are also configured to receive MR signal. The data collected by the auxiliary coils are processed and combined with the data from the standard receive coil(s) to achieve contrast enhancement of the projection 2D images. The data processing and combination may include, but not limited to, forming weighted sum of complex—valued images that are reconstructed from MR signal acquired from the multiple receive coils.
While the preferred embodiments of the present invention have been shown and described herein, it will be obvious that such embodiments are provided by way of example only. Numerous variations, changes and substitutions will occur to those of skill in the art without departing from the invention herein. Accordingly, it is intended that the invention be limited only by the spirit and scope of the appended claims.
This application is related to Provisional Application U.S. Ser. No. 60/794,365, entitled “METHOD FOR TRACKING DEVICES WITH MULTIPLE RF TRANSIT CHANNELS”, filed Apr. 24, 2006, the contents of which are herein incorporated by reference and the benefit of priority to which is claimed under 35 U.S.C. 119(e).
| Number | Date | Country | |
|---|---|---|---|
| 60794365 | Apr 2006 | US |
