MRA of the Abdomen, Pelvis, and Lower Extremities

16 Pages·2014·2.76 MB·English

4/8/2014
NO DISCLOSURES
MRA OF THE ABDOMEN,
PELVIS & LOWER
EEXXTTRREEMMIITTIIEESS
Bilal Tahir, MD
Assistant Professor of Clinical Radiology
Indiana University SOM Dept of Radiology & Imaging Sciences
Director of Abdominal Imaging, EskenaziHealth
OUTLINE
•Introduction
•Review of pertinent anatomy
•MRA Sequences
•MRA indications in the abdomen, pelvis, and lower extremities
•What does the radiologist look for when evaluation imaging?
•Pitfalls & Artifacts ---decrease image quality
•CTA vs. MRA
•Conclusion
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MRA TECHNIQUES
•Noncontrast-enhanced
•Time-of-flight
•Phase contrast
••BBllaacckk bblloooodd
•Steady state free precession
•Contrast-enhanced
•3D Gad
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TOF TOF
•Gradient echo sequence •Arteries or veins can be
•Flow-related selectively imaged
enhancement through the use of
ssaattuurraattiioonn bbaannddss
•Unsaturated blood bright
•Stationary tissues saturated
(dark)
FLOW DIRECTION: TOF FLOW DIRECTION
3D Gd MRA Time-of-flight
PHASE CONTRAST PHASE CONTRAST: VELOCITY
ENCODING
•Uses bipolar gradient
•Must know velocity of blood to be imaged in advance to select correct
•Stationary tissues velocity encoding parameter
experience no phase shift •Modifies bipolar gradient strength such that selected velocity induces a 180
((ddaarrkk)) ddeegg pphhaassee sshhiifftt
•Flowing blood experiences •Flow direction can be displayed
phase shift (bright)
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PC: VELOCITY ENCODING FLOW DIRECTION: PC
5 cm/s 80 cm/s Phase contrast MRA of portal vein
BLACK BLOOD 3D GAD MRA
•Eliminate signal from •3D gradient echo
flowing blood •Based on paramagnetic
•Saturation bands effect of gadolinium
••DDoouubbllee IIRR tteecchhnniiqquuee ((sshhoorrtteennss TT11 ooff bblloooodd))
•Eliminates many artifacts
associated with non-
contrast MRA
3D GAD
LINEAR
3D GAD MRA
enhancement
•Requires that the portion of k-space responsible for image contrast (center)
be filled when the contrast bolus peaks in the vessel of interest
Bolus
High High
resolution resolution
High contrast
K-space
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CENTRIC
FILL CENTER OF K-SPACE TOO EARLY
enhancement
Bolus
High High
Contrast Resolution
K-space
LATE TIMING RIGHT TIMING
•Educated guess (smart technologist)
•Timing bolus
•Automatic bolus detection (smart prep)
•Real-time monitoring
•Time-resolved MRA
Venous contamination
CLINICAL INDICATIONS CLINICAL INDICATIONS
•Abdominal Aortic Aneurysm: Interventional Planning and Follow-up •Non-traumatic Aortic Disease
•Claudication —Suspected Vascular Etiology •Pulsatile Abdominal Mass, Suspected Abdominal Aortic Aneurysm
•Follow-up of Lower Extremity Arterial Bypass Surgery •Recurrent Symptoms Following Lower Extremity Angioplasty
•Imaging of Mesenteric Ischemia •Sudden Onset of Cold, Painful Leg
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ABDOMINAL AORTIC ANEURYSM:
INTERVENTIONAL PLANNING AND
ACR APPROPRIATENESS CRITERIA
FOLLOW-UP
•Rating Scale •Planning for EVAR or open repair
•1,2,3 ---Usually not appropriate •MRA Abdomen & Pelvis without & with contrast ---ACS (Appropriateness
•4,5,6 ---May be appropriate Criteria Score) = 6.
•7,8,9 ---Usually appropriate •Alternatiive to CTA iin patiients wiith known AAA not iinvolviing the thoraciic
aorta and in whom iodinated contrast is contraindicated
•MRA Abdomen & Pelvis without contrast ---ACS = 4
•Appropriate for patients with severe renal dysfunction.
FOLLOW-UP FOR POST-
ENDOVASCULAR REPAIR (EVAR) OR
OPEN REPAIR OF AAA
•MRA Abdomen & Pelvis with & without contrast ---ACS = 7
•Appropriate alternative to CTA, but less accurate for assessing endograft
metallic components.
•Effffectiiveness depends on composiitiion off endoprostheiis.
•3D contrast enhanced MRA and time-resolved MRA are highly sensitive for
endoleaks.
•MRA Abdomen & Pelvis without contrast ---ACS = 5
•Selectively useful for assessment of renal or mesenteric vasculature in
patients with contraindication to iodinated contrast.
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CLAUDICATION —SUSPECTED
FOLLOW-UP OF LOWER-EXTREMITY ARTERIAL BYPASS
VASCULAR ETIOLOGY SURGERY
ASYMPTOMATIC PATIENT
•MRA lower extremity without and with contrast ---ACS = 8 •MRA lower extremity without and with contrast ---ACS = 3
•MRA lower extremity without contrast ---ACS = 5 •MRA lower extremity without contrast ---ACS = 2
•Appropriate in patients with contraindications to iodinated and gadolinium-
based contrast agents
INFRAINGUINALVEIN GRAFT,
SYMPTOMTIC(PAIN, SWELLING, ISCHEMIA,
ABNORMAL ABI)
•MRA lower extremity without and with contrast ---ACS = 8
•MRA lower extremity without contrast ---ACS = 5
2D TOF. AORTOBIFEMORALGRAFT NONTRAUMATICAORTIC DISEASE
•MRA without and with contrast ---ACS = 8
•MRA without contrast ---ACS = 7
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PULSATILE ABDOMINAL MASS,
SUSPECTED ABDOMINAL AORTIC CE MIP
ANEURYSM
•MRA Abdomen without contrast ---ACS = 6
•MRA Abdomen without and with contrast ---ACS = 6
•Alternative to CTA.
•Unable to detect calcium.
DOUBLE IR FSE BLACK BLOOD
AORTIC DISSECTION
SEQUENCE
CHRONIC OR ACUTE MESENTERIC
ISCHEMIA
•MRA abdomen without and with contrast ---ACS = 7
•Longer when compared to CT.
•Limited in distal thrombosis/embolism or nonocclusivemesenteric ischemia.
•MRA abdomen without contrast ---ACS = 3
•Lower sensitivity and specificity than MRA that incorporates contrast.
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RECURRENT SYMPTOMS FOLLOWING
LOWER-EXTREMITY ANGIOPLASTY
CLAUDICATION
•MRA lower extremity without and with contrast ---ACS = 8
•Able to triage between catheter and surgical management
•Thus may substitute for other noninvasive studies
•MRA lower extremity without contrast ---ACS = 6
RECURRENT SYMPTOMS FOLLOWING
SUDDEN ONSET OF COLD, PAINFUL
LOWER-EXTREMITY ANGIOPLASTY
LEG
THREATENED LIMB
•MRA lower extremity without and with contrast ---ACS = 5 •MRA lower extremity without and with contrast ---ACS = 7
•Useful if angiography is not performed (ie, surgical treatment is necessary) •Distal abdominal aorta should be included
•MRA lower extremity without contrast ---ACS = 4 •MRA lower extremity without contrast ---ACS = 5
3D SUB + C MIP / 3D +C
RENOVASCULARHYPERTENSION
LEFT RENAL A. STENOSIS
•MRA abdomen without and with contrast ---ACS = 8
•Requires intravenous gadolinium contrast agents and is accurate in
diagnosing renal artery stenosis.
•MRA and CTA are alternatiive examiinatiions.
•MRA abdomen without contrast ---ACS = 6
•Somewhat less accurate alternative to MRA with contrast
•Considered appropriate for use in patients with impaired renal function
(ACS= 8).
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USUALLY NO ROLE
•Blunt Abdominal Trauma
•Upper Gastrointestinal Bleeding
MRA ARTIFACTS AND PITFALLS
CAUSES OF PSEUDO-
TOF: RETROGRADE FLOW
STENOSIS/OCCLUSION
•Retrograde flow (TOF) •Contrast too concentrated
•Wrong Venc (PC) •Contrast too dilute
•Cardiac Pulsation •Fat suppression
•Motion •Early imaging
•Vascular clips •Late imaging
•Metallic stents •Post-processing artifact
•Vessel outside acquisition volume •Vessel outside reconstruction
volume
•Positioning •Threshold too high (SSD)
•Extrinsic compression •Background projection
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