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Magnetic Resonance Angiography and techniques
- 1. ALWINE ANTO 2ND Year BSc RADIOGRAPHY STUDENT DEPT OF NIIR , NIMHANS, BENGALURU-29 MR ANGIOGRAPHY & TECHNIQUES
- 2. Human Vascular System Intra cranial Carotid Aortic Coronary Pulmonary Abdominal Renal Peripheral
- 3. VASCULAR ABNORMALITIES Stenosis Aneurysm Arterial Venous Malformation (AVM) Thrombus Plaque Internal bleeding
- 4. MRA TYPES MRA pulse sequences Dark Blood RARE IR Bright Blood CE MRA None-CE MRA TOF PC MRI SSEP RARE - Rapid acquisition with refocused echoes(FSE) IR - Inversion Recovery CE - Contrast enhanced TOF - Time-of flight PC MRI – Phase Contrast MRI SSFP – Steady-state free precession
- 5. TOF MRA Based on inflow effect with use of GRE sequence keeping * TR 40msec (to saturate stationary tissues) * TE 5msec (to reduce spin dephasing) Methods: -2D multislice -3D singleslab -3D multislice PRINCIPLE OF TOF - TOF is based on the effect of unsaturated spins inflowing into a region of saturated stationary spins
- 6. 2D vs 3D TOF MRA 2D TOF 3D TOF ↓ saturation effect ↑ saturation effect Slow as well as fast flow Fast flow Low spatial resolution High spatial resoultion Good for large FOVs Good for small FOVs Cerebral venography, abdominal and peripheral angiography Cerebral angiography
- 7. TOF MRA ADVANTAGES DISADVANTAGES Overestimation of stenosis in turbulent or very slow flow MethHbin thrombosed vessel may mimic blood flow. CSF pulsation artifact simulating vessel lesions. Susceptibility artifacts. Can be used in renal failure patients Can be used in patients allergic to gadolinium.
- 8. ARTIFACTS IN TOF MRA • SHINE THROUGH ARTIFACTS • FLOW REVERSAL ARTIFACT • VENETIAN BLOOD ARTIFACT(3D MRA ONLY) • SUSPECTIBILITY ARTIFACTS • IN-PLANE SATURATION ARTIFACT • STAIR STEP ARTIFACT
- 9. SHINE-THROUGH ARTIFACTS 3D TOF MRA showing shine through of high signal from hematoma (H) and fat (F) at skull base
- 10. FLOW-REVERSAL ARTIFACT 2D TOF MRA shows only right vertebral artery. No flow related signal in the left vertebral artery is seen. Contrast-enhanced MRA shows retrograde filling of left vertebral artery (subclavian steal phenomenon)
- 11. VENETIAN BLIND ARTIFACT (3D MRA ONLY)
- 12. SUSCEPTIBILITY ARTIFACTS Source image shows susceptibility field distortion due to aneurysm clip MRA shows spurious loss of flow in entire right middle cerebral artery due to susceptibility artifact from clip
- 13. IN-PLANE SATURATION ARTIFACT 3D-TOF MRA showing artifactual in-plane signal loss within both middle cerebral arteries 2D-TOF MRA shows artifactual in-plane signal loss in horizontal portions of both anterior tibial arteries
- 14. STAIR-STEP ARTIFACT (2D TOF ONLY) Mild "stair-step" artifact due to non- isotropic voxels Mild motion artifact causing horizontal banding on this 2D-TOF MRA of the aorta Severe artifacts with jagged edges due to gross motion for carotid TOF MRA study
- 15. CONTRAST ENHANCED MRA Test bolus timing method Fluoroscopic triggering Time-resolved imaging Three methods to determine arrival of MR contrast agent The gadolinium-based contrast agent is injected intravenously, usually into a central catheter or ante cubical vein. 20ml of Gd contrast injected at 2-3 ml/sec. Flush with 20-30ml of saline. 3D spoiled gradient echo based sequence. Min. TE and Min. TR.
- 17. CE MRA ADVANTAGES DISADVANTAGES BETTER SPATIAL RESOLUTION LESS TIME REQUIRED NO SUSCEPTIBILITY ARTEFCATS. SUBCLAVIAN PSEUDO- STENOSIS ARTIFACT SCANNING TOO LATE (VENOUS CONTAMINATION) SCANNING TOO EARLY (MAKI/RINGING ARTIFACT)