Concurrent MRI of multiple objects

• US 6,549,799 B2
• Filed: 04/18/2001
• Issued: 04/15/2003
• Est. Priority Date: 04/18/2001
• Status: Expired due to Term

• Current Assignee: Sunnybrook & Women's College Health Sciences Centre
• Original Assignee: Sunnybrook and Women's College Health Sciences Centre
• Inventors: Bock, Nicholas A., Henkelman, R. Mark
• Primary Examiner(s): Vo, Hieu T.
• Application Number:
  US09/837,913
• Publication Number:
  US 20020156362A1
• Time in Patent Office: 727 Days
• Field of Search: 600/422, 600/410, 600/411, 600/439, 600/440, 600/441, 600/443, 324/307, 324/309, 324/310, 324/312, 324/314, 324/300
• US Class Current: 600/422
• CPC Class Codes: G01R 33/3415 comprising arrays of sub-coils , i.e. phased-array coils with flexible receiver channels
• CPC Class Codes: G01R 33/365 Decoupling of multiple RF coils wherein the multiple RF coils have the same function in MR, e.g. decoupling of a receive coil from another receive coil in a receive coil array, decoupling of a transmission coil from another transmission coil in a transmission coil array
• CPC Class Codes: G01R 33/3664 Switching for purposes other than coil coupling or decoupling, e.g. switching between a phased array mode and a quadrature mode, switching between surface coil modes of different geometrical shapes, switching from a whole body reception coil to a local reception coil or switching for automatic coil selection in moving table MR or for changing the field-of-view G01R33/3671 takes precedence

Abstract

A plurality of objects are concurrently studied in a common MRI apparatus wherein the RF excitation is distributed to one plurality of K RF coils of N said pluralities of RF coils and one of each of said N is switched to a corresponding one of K RF receivers. The interaction of the several coils is further minimized by selectably detuning each coil except for an active coil(s).

Claims

1. Apparatus for the concurrent acquisition of images for a corresponding plurality of objects, comprising

(a) a polarizing magnet for maintaining a uniform magnetic field over a selected volume,

(b) magnetic gradient module for establishing a magnetic gradient of selected direction and selected magnitude over said sensitive volume,

(c) a first plurality of K groups of RF cells, K>

1, each said group comprising N said cells, each said RF cell defining a subspace of said sensitive volume for containing one of said plurality of objects,

(d) an RF power source switchable to selected one of said K groups and distributed concurrently to each said plurality of N said cells,

(e) a plurality of N RF receivers, each said receiver deriving a signal selected from corresponding said cells of said K groups,

each said RF cell comprising a transmit/receive isolator for isolated communication between said RF source or said corresponding RF receiver and an RF coil,

a controller providing excitation control signals to said RF power source to direct RF power to said selected group, and providing receiver signal derivation logic to said plurality of N receivers.

2. The apparatus of claim 1 wherein said RF power source comprises a high power RF switch.

3. The apparatus of claim 2 further comprising an RF power divider for distributing RF power to each of said plurality of N cells.

4. The apparatus of claim 1 further comprising an N pole, K throw switch whereby each said N receivers derive said signal selected from corresponding cells of one said K groups.

5. The apparatus of claim 1 further comprising reactance selectably activated for a respective RF coil to detune said RF coil upon activation thereof.

6. The apparatus of claim 5 wherein said controller generates detuning control logic signals for activation of selected said reactances.

7. The apparatus of claim 1 wherein said transmit receive isolator comprises a quadrature hybrid.

8. The apparatus of claim 1 wherein said RF coil comprises a birdcage coil.

9. The apparatus of claim 8 wherein said quadrature hybrid provides quadrature components of said RF power and said birdcage coils is excited in quadrature.

10. The apparatus of claim 1 further comprising an acquired signal processor for processing signals derived from each said N receivers and associating said acquired signals with the respective object.

11. An array of RF coils disposed in mutual proximity, each said coil comprising a resonant frequency, each said coil comprising a corresponding auxiliary impedance, each said auxiliary impedance selectably capable of coupling to said corresponding coil, whereby said selected coupling shifts the resonant frequency of said corresponding coil.

12. The array of claim 11 wherein said auxiliary impedance comprises a switch wherewith said selective capability is implemented.

13. The array of claim 12 wherein said switch comprises a PIN diode.

14. The method of improving the isolation of an array of normally resonant RF coils from one said normally resonant RF coil, comprising

providing a respective electrically floating conductor in close proximity to each corresponding RF coil, said conductor having at least two terminals and substantially incapable of supporting a circulating current,

for each said RF coils except said one RF coil, activating an electrical connection between said respective terminals whereby each said conductor supports a circulating RF current and said corresponding RF coil is detuned from the normally resonant parameters thereof.

15. The method of improving the isolation of an array of normally resonant RF coils from one said normally resonant RF coil, comprising

providing a respective electrically floating conductor in close proximity to each corresponding RF coil, said conductor having at least two terminals and substantially incapable of supporting a circulating current,

for said one RF coil, activating an electrical connection whereby said conductor of said supports a circulating RF current between said terminals thereof and said corresponding RF coil is detuned from the normally resonant parameters thereof.

16. The method of concurrently obtaining magnetic resonance images of a plurality of N×

K objects within a controllable magnetic field distribution, N>

1 and K>

1, comprising the steps of

(a) associating said objects into K identifiable groups,

(b) selecting a K^th group of N said objects forming an active group,

(c) coupling RF power to each said objects of said active group to effect an excitation portion of a desired magnetic resonance pulse sequence, manipulating said controllable magnetic field in accord with said desired pulse sequence at prescribed values of parameters of said pulse sequence,

(d) directing inputs of N RF receivers to corresponding ones of said active group of N objects whereby respective free induction decay signals are acquired,

(e) storing said free induction decay signals as data sets identifiable with respective ones of said objects obtained at said prescribed values,

(f) repeating steps (c) through (e) for a sufficient variation in values of said parameters to obtain a representation within said free induction decay signals to express a portion of k-space for each said objects of said active group,

(g) selecting a different value of K to identify another group as the active group,

(h) repeating steps (b) through (g) until all values of K have been selected, whereby representations of the corresponding portions of k-space for all K groups have been obtained,

(i) repeating steps (b) through (h) until data sets representative of the entire k-space have been acquired, and

(J) processing each said data sets to obtain spatial images of said objects.

17. The method of claim 16 wherein said magnetic resonance pulse sequence comprises a 3 dimensional fast echo sequence.

18. The method of claim 16 wherein said step (g) further comprises removal from each said image of artifact attributable to the presence of others of said N×

K−

1 objects.