Peripheral Vascular MR Angiography

• Indications

• Equipment

• Technique

• Image Analysis

• Example Cases

• Reporting - Billing

Thank YouYi 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

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 hour 3D 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 minTotal 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 sec 32.5 sec28.4 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

Station 1 = pelvis

Station 2 = thigh

Station 3 = calf

scan delay

Centers of k-space

Time to venous contamination = 60 seconds

0 10 30 45 65

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 Positioning2D 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 (128-256)

Phase FOV = 0.8 (1-0.6)

Bandwidth = 31 (31 or 62)

3D Gadolinium Bolus Chase MRA

• Breathhold 1st 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 MIPCoronal 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 # Patients Technique Sensitivity Specificity

Owen (NEJM) 1992 23 2D TOF superior to DSA

Baum (JAMA) 1995 155 2D TOF 82 84

Prince (Radiology) 1995 43 3D Gd 94 98

Snidow (Radiology) 1996 32 3D Gd 100 98

Hany (Radiology) 1997 39 3D Gd 93-96 96-100

Ho (Radiology) 1998 28 Bolus chase 93 98

Meaney (Radiology) 1998 20 Bolus Chase 81-89 91-95

Yamashita (JMRI) 1998 20 3D Gd 96 83

Lee (Radiology) 1998 23 2D Gd 94 91

Winchester (JMRI) 1998 22 2D Gd 90 98

Link (Radiology) 1999 67 3D Gd 100 83

(post stent)

Reporting

Useful DescriptorsDescriptor Meaning

• Occluded

• Severe stenosis > 75% narrowing

• Moderate stenosis 50-75%

• Mild stenosis < 50% narrowing

• Normal normal

• Widely patent wide open: +/- tortuosity

+/- atherosclerotic irregularity• Ectatic diameter < 50% more than normal

• Aneurysmal diameter > 50% over normal

Useless Descriptors

Descriptor Meaning• 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