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Colóquio IFSC - Março /2011. Instrumental basis for an MRI/MRS center dedicated to animal studies. A. Tannús – 03/2011 IFSC - USP. Basic Principles; Some methodologies for fast imaging; NMR probes; Digital NMR spectrometer. Major items of this talk:. Basics. Basic Principles;

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major items of this talk
Basic Principles;

Some methodologies for fast imaging;

NMR probes;

Digital NMR spectrometer

Major items of this talk:

Basics

major items of this talk1
Basic Principles;

Some methodologies for fast imaging;

NMR probes;

Digital NMR spectrometer

Major items of this talk:
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!!

Probes: why focus on them?
transmit receive x split coils
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

5

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1

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2

1

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5 

Potential

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

Possible resonant structure

transmit rf coils
Transmit RF coils

Tune & match rods

RF reference potential

RF coil

our best approach double crossed saddle
Our best approach: Double Crossed Saddle

Tune & match circuit

“Double crosses” (outperforms) the equivalent Birdcage structure

other structures developed and tested
Other structures developed and tested:

8-leg transmit birdcage

16-leg transmit birdcage

latest developed probe receiving coils for rodents surface coils
Latest developed probe:Receiving coils for rodents – surface coils

C

CM

C

C

CT

RFout

Tune & match circuit on reception

rodents brain surface coils
Rodents brain surface coils*:

Anesthetics mask

Motion restriction

* Tested also as transmit/receive

results double crossed saddle
Results: Double Crossed Saddle

Actually a 20/30 system for now

results rodents surface coil
Results: Rodents surface coil

Actually a 20/30 system for now

is manganese contrast possible at 2 t

A

B

C

Is Manganese contrast possible at 2 T?

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

yes of course and more
YES, of course!! And more!

3 consecutive slices of a control animal showing hippocampus anatomy

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

Passive

TF

Signal

RF pulse

Active

“Cross-over”

effect

TF

Signal

RF pulse

to come soon phased array reception coils
To come soon: phased array reception coils

Preamp

Low Z

Preamp

Low Z

Preamp

Low Z

Preamp

Low Z

To the 4 BRUKER RECEIVERS

major items of this talk2
Basic Principles;

Some methodologies for fast imaging;

NMR probes;

Digital NMR spectrometer

Major items of this talk:
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
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.

Digital MR Spectrometer: Driving forces
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)!

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

Our proposal: develop a Digital MRI/MRS Spectrometer in two independent approaches:
mr state machine approach

To

all

modules

Sequencer

D/A

D/A

D/A

D/A

Loader

To all

modules

.

.

.

RF

Synthesis

Time

Base

MR State Machine approach

High

Speed

BUS (10 GB)

Receiver

demodulation

1 or

more

receivers

RF (NMR)

P

C

FIFO

A/D

PreCompensation

(preemphasys)

X

Generation

of Logical

Gradients

Conversion

to physical

Gradientes

P

C

Y

BUS

Z

B0

Modulation

AM

FM

Phase

RF

D/A

Different instances of the same concept of our State Machine

1 or more

Modulators

To all

receivers and

modulators

FPGA

system peripherals
System peripherals

Low speed external bus for Gradients

High speed external bus/ external SDRAM

Fast A/D and D/A converters

(85/125 MHz,

2 Transmit/ receivers for now)

Gradients DACs

(1us/point, 4 units)

old fashioned experimentalists are now free again

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!

Students:

Daniel Papoti (DOU)

Jackeline Malheiros (DOU)

Felipe Coelho (IC)

ChristoferBertonha (IC)

Tiago Martins (IC)

Cintia Silva (DTI)

Our team:

Edson Vidoto

Mateus Martins

Alberto Tannús

Rafael Martins (ITI)

Jorge Sampaio (DTI)

Mario Gazziro (DTI)

Diogo Queiroz (MES)

Cristina Torres (MES)

Gustavo Frigieri (PD)