peripheral vascular mr angiography indications equipment technique image analysis example cases...
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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