Transcript No Slide Title

Peripheral Vascular
MR Angiography
• Indications
• Equipment
• Technique
• Image Analysis
• Example Cases
• Reporting - Billing
Thank You
Yi Wang, PhD
Richard Watts, PhD
Priscilla Winchester, MD
Neil Khilnani, MD
David Trost, MD
Craig Kent, MD
Bernie Redd, MD
Qian Dong, MD
Jim Meaney, MD
Vince Ho, MD
Tom Chenevert, PhD
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
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
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
3 Critical Details
• Positioning
Unsubtracted
• Bolus timing
• Subtraction
Subtracted
Bolus Chase MRA
Technique
• 2D Projection MRA (timing):
• Floating Table
– Sag Loc
– Axial Loc
– Cor 3D-Gd-MRA
+ Pre
+ During
• 3D phase contrast (renals)
1 min
7 min
1 min
3 min
1.5 min
1.5 min
7 min
Total Imaging Time
15 min
Total Exam Time
<1 hr
2D Projection MRA: ankle-feet
Raw image
Complex subtraction
Left
Right
Coronal T1
2D Projection MRA: + complex subtraction
Ankles
Knee
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
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
6
Station 1 = pelvis
Station 2 = thigh
6
Station 3 = calf
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
Trifurcation
Overlap Common
Femoral Bifurcation
Bolus Chase Positioning
2D TOF
Internal
iliac
P 60
A 25
Common
femoral
Popliteal
P 45
A 30
Ankle
P 20
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
Coronal MIP
Oblique 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
Owen (NEJM)
1992
Baum (JAMA)
1995
Prince (Radiology) 1995
Snidow (Radiology) 1996
Hany (Radiology) 1997
Ho (Radiology)
1998
Meaney (Radiology) 1998
Yamashita (JMRI) 1998
Lee (Radiology) 1998
Winchester (JMRI) 1998
Link (Radiology) 1999
# Patients Technique
23
155
43
32
39
28
20
20
23
22
67
2D TOF
2D TOF
3D Gd
3D Gd
3D Gd
Bolus chase
Bolus Chase
3D Gd
2D Gd
2D Gd
3D Gd
(post stent)
Sensitivity Specificity
superior to DSA
82
84
94
98
100
98
93-96
96-100
93
98
81-89
91-95
96
83
94
91
90
98
100
83
Reporting
Useful Descriptors
Descriptor
•
•
•
•
•
•
Occluded
Severe stenosis
Moderate stenosis
Mild stenosis
Normal
Widely patent
• Ectatic
• Aneurysmal
Meaning
> 75% narrowing
50-75%
< 50% narrowing
normal
wide open: +/- tortuosity
+/- atherosclerotic irregularity
 diameter < 50% more than normal
 diameter > 50% over normal
Useless Descriptors
Descriptor
• Stenotic
• Patent
Meaning
“I think there is a stenosis”
“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