MR Angiography basic techniques and principles

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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

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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

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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
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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