colóquio ifsc - março/2011 instrumental basis for an mri/mrs center dedicated to animal studies a....

Colóquio IFSC - Março/2011

Instrumental basis for an MRI/MRS center dedicated to animal studies

A. Tannús – 03/2011IFSC - USP



Major items of this talk:

Basic Principles; Some methodologies for fast imaging; NMR probes; Digital NMR spectrometer

Basics


Probes: why focus on them?

Diversity of anatomies – no single probe for all studies; Studies at the limit of sensitivity; Large number of nuclei of interest; Methodologies requiring dedicated hardware (e. g.

split transmit coil ASL – avoid MT); Flexibility of studies – would you touch a US$35k

probe to configure it for a new experiment? Better build your own!!


Transmit/receive x split coils:

Compromise between uniformity and sensitivity:We can’t get everything with a single coil!

Uniform (transmit) coils require more power, consequently are less sensitive (uniform flip angle);

Efficient anatomic coils show poor RF field homogeneity – must be used as receive-only – since they present good sensitivity.


The problem in Electromagnetism to be solved: surface current in a cylinder.

xJ

BzJJ s ˆ2

ˆ sin 0010

1For a uniform perpendicular to z:B

1 2

4567

8

1 23

4567

8

3

12

3

4

5

6 7

8

12

3

4

56

7

8

Potenti

al

Possible resonant structure


Transmit RF coils

RF reference potential

RF coil

Tune & match rods


Our best approach: Double Crossed Saddle

Tune & match circuit

“Double crosses” (outperforms) the equivalent Birdcage structure


Other structures developed and tested:8-leg transmit birdcage

16-leg transmit birdcage


Latest developed probe:Receiving coils for rodents – surface coils

C

C C

CM

CT

RFout

Tune & match circuit on reception


Rodents brain surface coils*:

* Tested also as transmit/receive

Anesthetics mask

Motion restriction


Results: Double Crossed Saddle

Actually a 20/30 system for now


Results: Rodents surface coil

Actually a 20/30 system for now


Is Manganese contrast possible at 2 T?A B C

Coronal images of: control (A, animal 7), 36 h after 60 mg/kg of manganese chloride (B, animal 4,) and after 30 minutes in SE (C, animal 8) – 3D Flash enhances the hippocampus.

Answer: YES


3 consecutive slices of a control animal showing hippocampus anatomy

YES, of course!! And more!

Same 3 slices of an animal with 9 months of epileptic life: Notice the size of the ventricles, due to a downsizing hippocampus and other structures not yet associated to the SE. Open field of investigation.


Featuring: active transmit decoupling allows use of any sort of Adiabatic Pulses

Passive

Signal

“Cross-over” effect TF

RF pulseActive

TF

RF pulse Signal


To come soon: phased array reception coils

PreampLow Z

PreampLow Z

PreampLow Z

PreampLow Z

To the 4 BRUKER RECEIVERS


Digital MR Spectrometer

“Old fashioned electronics” systems could be home made up to the early 90’s:• Limiting factor: Bus speed.

Old fashioned experimental researchers (and newcoming) moved to software development;

Electronic devices became highly specific:• You can’t build what you want, only what the

functionality of the devices would allow you!!


Digital MR Spectrometer: Driving forces Commercial systems are expensive and

sometimes poor in flexibility; Our “Dream System” should be something like

waking up with a new problem, implementing it at morning, perform the experiments in the afternoon and having the paper ready at night!

Our experience with existing systems was a series of frustrations.


Good news from Field Programmable Array Logics devices (FPGAs):

Reached speed, density and programmability friendship to allow “mere mortals” to use them.• Modern FPGAs (Statix IV family, Altera and Virtex 6,

Xilinx) can accommodate few 4-core Intel CPU (code for that is somewhere over the internet).

Development kits come on all flavors, just choose the one that fits your problem (from US$40 to US$9k)!


Our proposal: develop a Digital MRI/MRS Spectrometer in two

independent approaches:

Using ALTERA’s embedded NIOS DSPs (Intellectual Property of ALTERA, we have a working University Agreement);

Using our own proprietary MR State Machine instantiated and adapted for all needed spectrometer subsystem modules


MR State Machine approach

Different instances of the same concept of our State Machine

FPGA


Development workstation


Stratix III development kit


System peripherals

Fast A/D and D/A converters(85/125 MHz,2 Transmit/ receivers for now)

Low speed external bus for Gradients

Gradients DACs (1us/point, 4 units)

High speed external bus/ external SDRAM


1 u2

u1

x1

Div 2

ToR

M S

PE

CT

u2

u1

x2

x1 RS

232

2

u1

x2

x1Seria-

lizador

u1

x2

x1Seria-

lizador

u1

x2

x1Seria-

lizador

u1

x2

x1Seria-

lizador

FPGA Top Level

Clock DAC Serial

16

16

16

16

Hard Reset

SysResetDiv2RS232

14 14

RF DAC

RF ADC50 Mhz

100 Mhz100 Mhz

8

8Digital I/O

DACs Serial

24

SDI, CS, LDAC

3

3

3

3

2

2

2

2

3

3

50 MhzSys Clk

Rx Clk

Tx Clk

USB ControllerProcessor

32ioData

16oADDR

4CS_n, OE_n, WE_n, RST_n

32

32

22

32

2


T Processor

RegistersBank

Timer

Latch

Control

RAM dual PortPROGRAM1K / 61 bits

61

12

61Data In

Data Out

Address

RunWrRd

Finish

Interrupt

AllReady

Ready

Triggers

Ad

dr

Writ

e

Rea

dA

dd r

Wrt

Ad

dr R

d

Da

ta R

e ad

Dat

a W

rite

Time32

EndTime

Line Out

Load

SysReset

Sys Clk50 Mhz

Latch Gate

INSTRUCTIONS

ENDOUTJMP

IFWAIT FLAGS

READYSET INTERRUPT

RETURNSTART LOOP

END LOOPSTART LOOPX

OUTXLOAD

IF REGOUTD

LOAD S0


Old fashioned experimentalists are now free again!!

Please join us on learning, using, teaching your students and convincing others that this new concept of doing electronics is

excitingly feasible!

Our team:

Edson Vidoto

Mateus Martins

Alberto Tannús

Students:Daniel Papoti (DOU)Jackeline Malheiros (DOU)Felipe Coelho (IC)Christofer Bertonha (IC)Tiago Martins (IC)Cintia Silva (DTI)

Rafael Martins (ITI)Jorge Sampaio (DTI)Mario Gazziro (DTI)Diogo Queiroz (MES)Cristina Torres (MES)Gustavo Frigieri (PD)


Thank you!

colóquio ifsc - março/2011 instrumental basis for an mri/mrs center dedicated to animal studies a....

Documents

colquio ifsc maro2011

birdcage slide

reception slide

animal studies

digital mrimrs spectrometer

poor rf field homogeneity

studies studies

control animal