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Peripheral Vascular MR Angiography
Indications Equipment Technique Image Analysis Example Cases Reporting - Billing
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Thank You Yi Wang, PhD Qian Dong, MD Richard Watts, PhD Jim Meaney, MD
Priscilla Winchester, MD Vince Ho, MD Neil Khilnani, MD Tom Chenevert, PhD David Trost, MD Craig Kent, MD Bernie Redd, MD
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Indications: Intermittent Claudication Non-healing ulcer
Post bypass graft Aneurysm Pre free-flap Pediatric
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Indications for MRA Difficult access Renal insufficiency Cr > 2.0
Allergy to iodinated contrast Patient refuses conventional angiography
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Advantages of MRA No nephrotoxicity Allergic reactions rare 3D
Anatomy and Physiology High Accuracy Affordable (reimbursement = $1159)
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Advantages of Gadolinium
No pulsatility artifact No slice misregistration No in-plane saturation High resolution (1.8 x 1.6 x 2.6 mm) Fast
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Equipment for Peripheral MRA
Magnet: 1.5 Tesla high SNR 0.5 Tesla requires more Gd High performance gradients Coil: body and head coil Injector vs hand injection Foam and straps
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Table Positioning Pole
PVC tubing 2 inch diameter 3-4 meters long holes at 36 or 40 cm spacings
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Table Positioning Blocks
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Technique: younger vs older
Young Adult Older patient 2D TOF Tech (30 years old) 2D TOF Radiologist (41 years old) 2D TOF: 1 hour 3D Gd MRA: 87 seconds 3
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Technique Pediatric – Young Adult (fast flow)
Head or extermity coil 2D time-of-flight Gd almost never necessary Gating +/- Older Patients (slow flow) Head coil 2D projection MRA of ankle-feet Body coil 3D Bolus chase MRA: Renals distal calf 3D phase contrast of renal arteries
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3 Critical Details Positioning Bolus timing Subtraction Unsubtracted
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Bolus Chase MRA Technique
2D Projection MRA (timing): 1 min Floating Table min Sag Loc min Axial Loc min Cor 3D-Gd-MRA Pre min During min 3D phase contrast (renals) 7 min Total Imaging Time min Total Exam Time <1 hr 7
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2D Projection MRA: ankle-feet
Raw image Complex subtraction Left Right Coronal T1
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2D Projection MRA: + complex subtraction
Ankles Knee 9
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2D Projection MRA (Left foot)
20.3 sec 24.4 sec 28.4 sec 32.5 sec 72.7 sec Time to fill distal station = 24 seconds Time to fill pelvis = 2/3 (24 sec) = 16 sec Time for venous contamination = 60 sec
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Calculation of Bolus-Chase Injection Timing Parameters
Time to venous contamination = 60 seconds Time to fill pelvis = 16 seconds Centers of k-space scan delay 6 Station 1 = pelvis 6 Station 2 = thigh 6 Station 3 = calf 10 30 45 65 8
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Bolus Chase MRA Preparations
level legs secure feet with curlex determine length of stations landmark above umbilicus 11
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Overlap Common Femoral Bifurcation
Position for Overlap at Critical Sites Overlap Trifurcation Overlap Common Femoral Bifurcation
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Bolus Chase Positioning
2D TOF P 60 P 20 P 45 A 25 A 30 Internal iliac Ankle Popliteal Common femoral
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Selecting Imaging Parameters
Slice thickness = 3 (2-5) mm # of slices = 28 (20-40) Frequency = 256 Phase = 160 ( ) Phase FOV = 0.8 (1-0.6) Bandwidth = 31 (31 or 62)
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3D Gadolinium Bolus Chase MRA
Breathhold 1st station Use oxygen liberally Scan delay ~ 10 sec 15
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Image Post Processing Digital subtraction: pre from post
Complex Fourier Subtraction Do not subtract MIPs MIP subtracted source images Reformat into lateral & oblique projections Subvolume MIPs for selected regions renal arteries mesenteric arteries common femoral bifurcations regions of greatest interest Examine pulsatility artifact on 2D TOF images 16
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Oblique views obtained by reformatting data on computer even after patient leaves
Oblique MIP Coronal MIP
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Popliteal Artery Aneurysm
Male>>> female Risk of complications thrombosis => high emboli => high rupture => low Associated with other aneurysms
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Patient could not straighter knee
2D Projection MRA
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Peripheral Vascular MRA
Year # Patients Technique Sensitivity Specificity Owen (NEJM) D TOF superior to DSA Baum (JAMA) D TOF 82 84 Prince (Radiology) D Gd 94 98 Snidow (Radiology) D Gd Hany (Radiology) D Gd Ho (Radiology) Bolus chase 93 98 Meaney (Radiology) Bolus Chase Yamashita (JMRI) D Gd 96 83 Lee (Radiology) D Gd 94 91 Winchester (JMRI) D Gd 90 98 Link (Radiology) D Gd (post stent)
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Reporting
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Useful Descriptors Descriptor Meaning Occluded
Severe stenosis > 75% narrowing Moderate stenosis % Mild stenosis < 50% narrowing Normal normal Widely patent wide open: +/- tortuosity +/- atherosclerotic irregularity Ectatic diameter < 50% more than normal Aneurysmal diameter > 50% over normal
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Useless Descriptors Descriptor Meaning
Stenotic “I think there is a stenosis” Patent “I see the artery”
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MRA Summary No Ionizing Radiation No Contrast Injection necessary
If Contrast No nephrotoxicity Reformat to obtain an view Anatomy and Physiology High Accuracy Tremendous Future
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