منهج مادة الرنين المغناطيسي الفرقة الأولي شعبة الأشعة الدراسات التخصصية

منهج الرنين المغناطيسي 
الفرقة الأولي شعبة الأشعة

الدراسات التخصصية

مقتطافات نصية

Introduction

MRA stands for magnetic resonance angiography. MRA of brain is used to assess abnormalities in the arterial blood supply system of brain. 3-dimensional (3D)  time-of-flight (TOF) MRA is the most common technique used to assess the arterial blood supply system of brain. 3D TOF provides higher signal-to-noise and shorter imaging times. MRA brain is easy to perform and does not require contrast administration.

Time-of-flight (TOF)

These techniques derive contrast between stationary tissues and flowing blood by manipulating the magnitude of the magnetization. The magnitude of magnetization from the moving spins is very large compared to the magnetization from the stationary spins which are relatively small. This leads to a large signal from moving blood spins and a diminished signal from stationary tissue spins. Time of flight (TOF) utilizes the longitudinal magnetization vector for imaging. The 3D acquisition allows for thinner slices with smaller voxel size (.6-1mm).

Indications for MRA brain

1.Aneurysm, Stroke, Vasospasm, Vasculitis
2.Internal Carotid Artery Occlusion and Stenosis
3.Cerebral Artery Occlusion and Stenosis
4.Basilar Artery Occlusion and Stenosis 
5.Arteriovenous malformation (AVM) 
6.Atherosclerotic Disease

FLAIR is another variation of the inversion recovery sequence. In FLAIR, the signal from fluid is nullified by using a long effective echo time and long inversion time. Inversion recovery sequence with a long inversion time (TI) of 2000-2500 is used for fluid suppression. This sequence is commonly used in the brain and spinal cord where the lesions are normally covered by bright cerebrospinal fluid (CSF) signals. A long inversion time suppresses the high CSF signal and improve the visualization of small periventricular and spinal cord lesions.

MRI image appearance

The easiest way to identify FLAIR images is to look for CSF filled spaces and lesions or other pathological processes in the brain or spinal cord. Fluids normally appear dark and lesions or other pathological processes appear bright on image. Images normally appear as a fluid suppressed T2 image.

Tissues and their FLAIR appearance

Bone marrow: - equal to or higher than that of muscle (fatty marrow is usually bright)
White matter - darker than gray 
Moving blood- dark 
Gray matter - gray 
Muscles -gray 
Fat – bright 
Fluids – dark
Bone - dark 
Air - dark

Pathological appearance

Pathological processes normally increase the water content in tissues. The added water component results in a signal increase on FLAIR images. Consequently, pathological processes are usually bright on FLAIR images.

Use

Very useful for brain imaging 
Useful for spine imaging

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عن ِAlasry