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MR Angiography basic techniques and principles

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Title: MR Angiography basic techniques and principles


1
MR Angiographybasic techniques and principles
  • Lawrence N. Tanenbaum, M.D. FACR
  • New Jersey Neuroscience Institute-Seton Hall
    University
  • JFK Medical Center Edison Imaging
  • www.drtmasters.com drt_at_drtmasters.com
  • Edison, New Jersey

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Time of Flight (TOF)
  • 2D, 3D
  • longitudinal magnetization difference MRA
  • flow related enhancement
  • challenges
  • saturation effects
  • dephasing due to complex motion

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Saturation effectsMRA principles
  • progressive saturation of blood as it passes
    through slice/slab
  • more severe in (thick) 3D slab than (thin) 2D
    slice
  • more significant for TOF than PC
  • manifest as loss of signal with in plane flow on
    2D
  • limits the functional size and coverage of 3D
    slabs

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Limiting saturationtechniques
  • MOTSA
  • Magnetization transfer
  • Variable flip angle (RAMP)

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MOTSAMultiple Overlapping Thin Slice Acquisition
  • hybrid of 2D and 3D techniques
  • 3D
  • resistance to in-plane saturation
  • high resolution
  • short TE
  • stacking of thin slabs minimizes saturation and
    allows unlimited coverage

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MRA brainaneurysm
  • vasc TOF SPGR
  • 14 / min / 20,16 kHz
  • 14 FOV, f AP
  • 1 mm / zip 0.5
  • 256 x 192
  • MOTSA 3 x 32, overlap 3
  • ramp IS
  • 1 nex, 429

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MRA brainaneurysm 8 ch
  • vasc TOF SPGR
  • 15 / min / 20, 25 kHz
  • 18 FOV, f AP
  • 1 mm / zip 0.5
  • 448 x 192, ASSET x 2
  • MOTSA 4 x 32, overlap 3
  • ramp IS
  • 1 nex, 319

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MRA brain 3T8 channel
  • vasc TOF SPGR
  • 14 / 2.3 / 20, 32 kHz
  • 18 FOV, f AP
  • 1 mm / zip 0.5
  • 512 x 224, ASSET x 2
  • MOTSA 4 x 32, overlap 3
  • ramp IS
  • 1 nex, 410

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multislab 3D TOF 512 x 224
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3D MOTSA TOF
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3DTOF MRA neck
  • TR / min / 20, ramp I-S
  • 18 / 12 FOV, f RL
  • 224 x 128 1024 ZIP
  • 2 mm / 1mm spacing (ZIP)
  • 16 kHz, 1 nex
  • 20 pps overlap 4, 6 slabs
  • 412

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Multislab 3DTOF
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Magnetization transfer
  • brain has a higher fraction of bound water than
    blood
  • MT pulses selectively excite bound water
  • result
  • relatively selective saturation of brain relative
    to blood
  • improved suppression of background tissues
  • superior flow/vessel visualization

17
MRA brainstroke
  • vasc TOF SPGR
  • 30 / min / 25, 16 kHz
  • 16 FOV, f AP
  • 1.6 mm / zip 0.8
  • 256 x 160, 512Z
  • 50 partitions, 1 slab
  • MT, ramp IS
  • 1 nex, 349

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MRA brainstroke 8 ch
  • vasc TOF SPGR
  • 26 / 2.0 / 25, 16 kHz
  • 18 FOV, f AP
  • 1.6 mm / zip 0.8
  • 448 x 192, ASSET x 2
  • 50 partitions, 1 slab
  • MT, ramp IS
  • 1 nex, 208

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Variable flip angleRAMP, TONE
  • increase in flip angle across slab in direction
    of flow
  • use with MT or MOTSA to limit saturation effects
  • no change in TE,TR

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Phase contrast (PC)
  • 3D, 2D
  • transverse magnetization difference MRA
  • velocity induced phase shifts
  • acquisition
  • set of GRE acquisitions with different bipolar
    gradients
  • subtraction leaves flow information
  • challenges
  • aliasing and signal loss due to improper VENC
  • dephasing due to complex motion

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Carotid occlusion
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Comparison of conventional and MRA
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fibromuscular dysplasia
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fibromuscular dysplasia
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Neurological applications
  • extracranial
  • symptomatic stenosis
  • ultrasound correlation and follow-up
  • intracranial
  • stenosis and occlusion
  • aneurysm
  • vascular lesions
  • sinus thrombosis

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Conventional angiography
  • gold standard for vessel morphology
  • inappropriate for screening
  • invasive
  • small risk of morbidity and mortality
  • costly
  • does not evaluate parenchymal disease

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Ultrasound
  • stenosis primarily via flow alteration
  • some morphologic information
  • non-invasive, relatively low cost (?)
  • does not evaluate parenchymal disease

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Ultrasound
  • operator dependent
  • limited area amenable to study
  • degraded by calcified plaque
  • difficulty with tortuosity
  • severe stenosis may mimic occlusion or bilateral
    disease

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TOF MR angiography
  • physiological more than structural
  • contrast comes from blood movement
  • rapid, uniform flow best assessed
  • complex flow leads to signal loss, exaggeration
    of length and severity of stenosis

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Neurological applications
  • extracranial
  • symptomatic stenosis
  • ultrasound correlation and follow-up
  • intracranial
  • stenosis and occlusion
  • aneurysm
  • vascular lesions
  • sinus thrombosis

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3D Conventional angiography
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basilar stenosis
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Intracranial aneurysm
  • aneurysms rupture in 18,000 NA per year
  • 50 die immediately
  • 50 of survivors die within 5 days
  • 50 of remainder suffer neurologic damage
  • only 12-15 with rupture emerge intact
  • surgery on unruptured aneurysm low
    morbidity/mortality

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Intracranial aneurysmMRA screening
  • high risk patients
  • strong family history
  • polycystic kidney disease
  • aortic coarctation
  • fibromuscular disease
  • collagen vascular disease
  • sickle cell disease
  • MRI required

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Intracranial aneurysmMRA role
  • DDx r/o aneurysm
  • evaluate / follow-up known aneurysm
  • acute SAH
  • urgent CT
  • conventional angio / CTA
  • MRA if conventional angio negative.

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ophthalmic artery 3.5 mm aneurysm
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3 wks s/p worst headache ever
right CN III Palsy pupil involved
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1024 MRA
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Intracranial aneurysmsMR angiography
  • 95 sensitivity, 100 specificity for detection
    of at least one 3 mm aneurysm
  • Ross AJNR 199011
  • No hemorrhage from aneurysm less than 3 mm
  • McCormick J Neurosurgery 197033
  • 99 of aneurysms associated with SAH occur within
    circle of Willis
  • Locksley, IAQSAH Cooperative Study 1969

69
New MRA techniques
  • high performance gradients
  • TE effects
  • advanced flow compensation
  • alternative rendering methods
  • interpolation (ZIP) techniques
  • Contrast Augmented MRA
  • gated TOF

3D EC TRICKS
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Aneurysm vs. loop
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Aneurysm vs. loop
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Aneurysm vs. loop
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TE 6.9
TE 2.9
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TE 2.9
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TE 4.8
TE 3.4
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Double-triple IR FSEblack blood
  • first non slice selective IR pulse inverts all
    spins
  • second slice selective pulse re-inverts spins in
    slice
  • TI time set to null blood (BLAIR) from outside of
    slice
  • e.g. 650 msec for HR 60 bpm
  • third (ST)IR pulse used to null fat
  • TI 150
  • may increase conspicuity of acute MI

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Arhythmigenic right ventricular dysplasia
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dissection ascending aorta TwinSpeed
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right atrial lipoma IRFSE ASSET Twin-E
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Plaque imaging
Mt. Sinai Medical Center, New York, NY, USA
91
Plaque imaging
fse-xl TR/TE 2RR/45.3/Ef. 100x100x3mm
256x256x2NEX ETL 16 RBW 31.2kHz EG/NP/VB/SQ/BSP
Univ. Dept. of Radiology, Cambridge, UK
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T2 FSE
GRE TOF
2ble IR
plaque characterization
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Plaque imaging
390mm x 390mm x 3mm
100x100x3mm 256x256 ETL 24 ST 44hbs
Univ. Dept. of Radiology, Cambridge, UK
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FIESTA
  • Fast Imaging Employing Steady-state Acquisition
  • Balanced SSFP / true FISP
  • balanced gradients rephase / refocus transverse
    magnetization (maintain phase coherence) at end
    of TR interval
  • SI proportional T2/T1 for very short TR

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FIESTA
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dissection ascending aorta TwinSpeed
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dissection ascending aorta TwinSpeed
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Aortic dissection
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FIESTA
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Hypertrophic cardiomyopathy
Johns Hopkins U
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FIESTA
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Mitral regurgitation
Valvular detail
Zurich Hospital
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JFK Medical Center
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