Mr i Principles

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Mr i Principles

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MRI

MRI : . . 0.3-1.5.

. Larmor . ppm, , .

. , .

. 0.5.

. .

0.35. .,, .

, -270 , (.. ) ( ). ' . 2.

shimming coils . Larmor . . shimming coils, shimming.

Gradient Coils . (x,y,z). , Larmor . (spatial enconding)( , ).

Radiofrequency Coils . (transmit), (receiver) -. , Larmor, .

.

-.

, ,, ... , .

. , , synthesizer, , .

, , .

. , , . .

, , . . . , .

(.. ) , .

;

, , . .

.

.

, .

, .

, (longitudinal)

, (precessing) , . , ,, .

. Larmor:

= . o

= ,= , = .

, :

1H2H13C31P

(MHz/Tesla)29,1642,5810,717,24

. .

.

. . . , XY . XY.

Larmor, . (RF) (.. ). (coils) .

(RF) , (,longitudinal, ), XY.

, xy. Larmor, xy. , Mxy .

.

. . ( ). .,, . . (longitudinal) . . (=0).

(in-phase). , XY,.

. XY , , . , .

XY Mxy.

:

, , Mz.

(in-phase), Mxy.

, . ,, . .

,, .

, , .

(out of phase), .

. Mz. , . 63% ( 63% Mz), 1 .

1 (,lattice), -,spin-lattice relaxation time.

Larmor. , , . , Larmor ... , . , , 1. 1 Mz. (CSF) (long) 1 , 2000-3000msec.

(short) 1, . 1 150-250msec.

1 1 , 1.5,920msec 790msec.

XY. (out of phase). (Mxy).

, 2. 2 37% .

2 , -,spin-spin relaxation time.

, , . Gradient Coils (spatial encoding). .

, . , , . , , (long) 2. , , (short) 2.

, 2. , 2*(T2 star). 2* 2.

PULSE SEQUENCES AND IMAGE CONTRAST . , .

(proton density) , 1 2 . . 1 2 , , .

, (,TR,Flip angle ,) .

. . .

Spin Echo.

SPIN ECHO Spin Echo 90 180, /2. XY. ( 1 2), 180 /2, , XY. (Echo Time, ) (spin echo), . . , 90 90, TR(Repetition Time, ).

:

90. ( , Y ).

(gradient coil) . .

/2 90 180. XY .

/2 180, 90, . , -- .

spin echo TR. pixel Spin Echo :

Sse(TE,TR)=N[H]e-TE/T2(1-e-TR/T1)

(FOV,matrix,NEX), [] pixel.

2 TR 1 . :

TR(80msec) 2 (2 weighted). :

Spin Echo T1 , , . 1 .

2 , , , .

1 1 . (short) 1, , (). (long) 1 , ENY, 1 , , .

2 ,, 2 . (long) 2 , , (). (short) 2 , , , , () 2 , , , , .

(proton density) . , , , . , , , .

:

Spin echo :

1 1 ( 1 , 1 ).

2 2 ( 2 , , 2 ).

(proton density) ( , ).

GRADIENT ECHO GRE , , . 1 180. , (Gradient Coils), (180), Spin Echo. Gradient Coils, ,, . gradient coils (..180), 90(.. 30 60), , 90, Spin Echo.

GRE Spin Echo 180, . GRE , , . 2, 2*(T2 star) GRE 2 2 . :

1/T2*=1/T2 + 1/T2.

O T2* 2 .

(contrast) GRE Spin Echo , (flip angle), . (TR) ( 45-70 ) 1 . (5-10 ) (proton density). (TE, 20-50msec) (TR,200-500msec) 2.

:

INVERSION RECOVERY IR 180, . , TI(Inversion Time), 90, XY . 180, (spin echo). 90 (read out), (Echo Time). TR.

Inversion Recovery 1 (TR,TE,TI).

, STIR(Short Tay Inversion Recovery) 1, 1 , 1 .

, 400-700msec, 1 , 1 , 1 . Spin Echo 1 .

:

Inversion Recovery :

Inversion Time(TI) 1 ( 1 , 1 ).

Inversion Time(TI> 400-700 msec) 1 ( 1 , 1 ).Artifacts artifact . . .

' . artifact service .

artifacts . .

artifact .

artifact , .

artifact . Aliasing, Chemical Shift artifact, Truncation, (Partial Volume Effect) artifact .

artifact (RF) Gradients. .. Crosstalk artifact, artifacts Eddy currents, artifact ...

artifact artifact (Magnetic Susceptibility), .

Artifact H Fourier(2D Fourier Transform). pixel , pixel (gray scale). (frequncy) (phase) pixel Y, .

, artifact. , (min). , (sec). pixel

(frequency enconding steps) milliseconts, (phase enconding steps) (min). artifact .

artifact .

, , , Parcinson.

artifact .

artifacts , . ECG ( R wave).

artifacts , .( ).

, .

, , artifacts. ' artifact breath hold , . , .

breath hold artifacts. respiratory gating respiratory compansation. respiration compansation respiratory gating to TR .

artifacts , , artifacts.

' artifact .

Artifact ( ) . .Artifact C. D .Artifact Artifact artifacts. (RF) , . (signal loss). , , flow void.

' , . ghost artifact, , .

spatial presaturation(SAT). , ., artifact.

.,, , (superior) (inferior) .

Saturation . Saturation inferior. C Saturation superior. H D Saturation inferior Superior. . (CSF), , . artifact, .

' artifact, gradient moment nulling( GE Flow Comp). (rephase) .' ghost artifact, CSF, CSF(myelograhic effect).

gating(pheripheral gating).

CHEMICAL SHIFT . 1.5,.., 220Hz, .

1.7pixel, ' .( 32kHz matrix 256).

.

.

artifact, (swap phase-frequncy). artifact , .

Wrap Around Aliasing artifact , (FOV), .

(FOV).

() .

, Backfolding Artifact . .

. No Phase Wrap. (FOV) 256 , 512( matrix 256). . FOV .

artifact . ,.. 32kHz 16kHz.

Truncation Artifact ( Gibbs) artifact , . Fourier(Fourier transform) (raw data) .

matrix,.. 128 . ,

, .. matrix 128 256 (FOV). Array Processor Array Processor .o .

artifacts (grid) .Artifact artifact , (RF) (shading areas) .

(FOV), 90 180 . . 90 180 . , .

,.

(Scan Room) .