Peripheral Vascular MR Angiography Indications Equipment Technique Image Analysis Example Cases Reporting - Billing

Thank You Yi Wang, PhDQian Dong, MD Richard Watts, PhDJim Meaney, MD Priscilla Winchester, MDVince Ho, MD Neil Khilnani, MDTom Chenevert, PhD David Trost, MD Craig Kent, MD Bernie Redd, MD

Indications: –Intermittent Claudication –Non-healing ulcer – Post bypass graft –Aneurysm –Pre free-flap –Pediatric

Indications for MRA Difficult access Renal insufficiency Cr > 2.0 Allergy to iodinated contrast Patient refuses conventional angiography

Advantages of MRA –No nephrotoxicity –Allergic reactions rare –3D –Anatomy and Physiology –High Accuracy –Affordable (reimbursement = $1159)

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

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

Table Positioning Pole PVC tubing 2 inch diameter 3-4 meters long holes at 36 or 40 cm spacings

Table Positioning Blocks

Technique: younger vs older 2D TOF: 1 hour3D Gd MRA: 87 seconds Older patientYoung Adult 2D TOF Tech (30 years old) 2D TOF Radiologist (41 years old)

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

Unsubtracted Subtracted 3 Critical Details Positioning Bolus timing Subtraction

Bolus Chase MRA Technique 2D Projection MRA (timing):1 min Floating Table 7 min –Sag Loc 1 min –Axial Loc 3 min –Cor 3D-Gd-MRA +Pre 1.5 min +During 1.5 min 3D phase contrast (renals)7 min Total Imaging Time 15 min Total Exam Time <1 hr

2D Projection MRA: ankle-feet Right Left Coronal T1 Raw image Complex subtraction

2D Projection MRA: + complex subtraction Knee Ankles

2D Projection MRA (Left foot) 20.3 sec32.5 sec 28.4 sec24.4 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

Calculation of Bolus-Chase Injection Timing Parameters Time to fill pelvis = 16 seconds 6 6 Station 1 = pelvis Station 2 = thigh Station 3 = calf 6 scan delay Centers of k-space Time to venous contamination = 60 seconds

Bolus Chase MRA Preparations level legs secure feet with curlex determine length of stations landmark above umbilicus

Position for Overlap at Critical Sites Overlap Common Femoral Bifurcation Overlap Trifurcation

Bolus Chase Positioning 2D TOF P 60 P 20 P 45 A 25 A 30 Internal iliac Ankle Popliteal Common femoral

Selecting Imaging Parameters A 24.8 P 60.2 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)

3D Gadolinium Bolus Chase MRA Breathhold 1 st station Use oxygen liberally Scan delay ~ 10 sec

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

Oblique views obtained by reformatting data on computer even after patient leaves Oblique MIP Coronal MIP

Popliteal Artery Aneurysm Male>>> female Risk of complications thrombosis => high emboli => high rupture => low Associated with other aneurysms

Patient could not straighter knee 2D Projection MRA

Peripheral Vascular MRA Year# PatientsTechniqueSensitivitySpecificity Owen (NEJM) D TOF superior to DSA Baum (JAMA) D TOF8284 Prince (Radiology) D Gd9498 Snidow (Radiology) D Gd10098 Hany (Radiology) D Gd Ho (Radiology) Bolus chase9398 Meaney (Radiology) Bolus Chase Yamashita (JMRI) D Gd9683 Lee (Radiology) D Gd9491 Winchester (JMRI) D Gd9098 Link (Radiology) D Gd10083 (post stent)

Reporting

Useful Descriptors DescriptorMeaning Occluded Severe stenosis> 75% narrowing Moderate stenosis50-75% Mild stenosis< 50% narrowing Normalnormal Widely patentwide open: +/- tortuosity +/- atherosclerotic irregularity Ectatic  diameter < 50% more than normal Aneurysmal  diameter > 50% over normal

Useless Descriptors DescriptorMeaning Stenotic“I think there is a stenosis” Patent“I see the artery”

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