Week 8 Flashcards
bandwidth is __ proportional to sampling time
inversely
high bandwidth RF pulse causes __
higher SAR = thicker slice thickness and reduced TEs & TRs
purpose of birdcage coil
provides best RF homogeneity & transceiver coil to image head
FLAIR
Fluid Attenuated Inversion Recovery
FLAIR nulls fluid signal by __
long inversion time
SWI
Susceptibility Weighted Imaging
SWI uses __ to generate unique contrast
magnetic susceptibility differences such as deoxygenated blood, Fe2+, & Ca2+
SWI is useful for __
microbleeds, calcifications, microhemorrhage
SWI images obtained are __
- Magnitude image
- Phase image
- SWI
- minIP
whole brain scans include __
- localizer
- axial T1 / T2 / FLAIR / DWI / SWI
- coronal T1
- sagittal T2
coronal brain scans are aligned to __
frontal sinus to line of occipital protuberance
coverage of whole brain scans
vertex to foramen magnum
whole brains scans are aligned to __
Anterior Commissure – Posterior Commissure (AC-PC) line
coronal epilepsy range is __
whole temporal lobe
coronal epilepsy scans are __
angled perpendicular to brain midline, tilted to hippocampus
orbit scans done include __
- localizer
- T1 coronal
- T2 axial / sagittal
- STIR axial / coronal
T1 coronal orbit scans are aligned __
Perpendicular to optic nerve, Position block parallel to eye lenses
T2 axial orbit scan position block are aligned __
parallel to optic nerve
T2 sagittal oblique orbits are aligned __
Parallel to line along superior & inferior rectus muscle; position block parallel to optic nerve
why is CT the 1st modality for emergencies instead of MRI
speed / availability / contraindications for MRI
common artifacts seen in time of flight MRA
- Venetian blind artifact due to overlapping adjacent slabs acquired separately then fused together
- Imperfect slab superimposition causes multiple overlapping thin slab acquisition which causes tortuous vessels being cut off and ‘stenosis’ appearance
how does time of flight work
Rapid RF pulses to saturate stationary protons in a slice before they can fully recover longitudinal magnetization
Surround tissues saturated using short TR to prevent T1 recovery and appears dark
Flowing blood unsaturated and appears bright
Moving protons do not experience saturation pulses & have longitudinal magnetization available for signal generation
subdural hemorrhage appears __
biconcave & venous blood
epidural hemorrhage appears __
biconvex & arterial blood
types of aneurysms
berry [bulges from 1 side of artery]
fusiform [bulges from all sides of artery]
mycotic [infected artery wall]
vascular diseases include __
aneurysm, arterial venous malformation, arterial venous fistula
what is multiple sclerosis
Autoimmune disease attacks protective sheath that covers nerve fibers & causes problems between brain & body
MRI face protocols
- localizer
- Axial T1 / STIR / DWI
- Sagittal T2
- Coronal T1 / STIR
- 3D T1
MRI face axial scan targets are __
- Position block parallel to hard palate
- Perpendicular to nasal septum
- Glabella down to larynx
MRI face sagittal position block parallel to __
nasal septum
MRI face coronal aligned __
- Perpendicular to nasal septum
- Positioning block perpendicular to hard palate
tongue sagittal range are __
- AP range = sphenoid sinus to clear nose tip
- RL range = entire oral cavity
MRI neck scans include
- localizer
- axial T1 / STIR / DWI
- sagittal T2
- coronal T1 / STIR
MRI neck axial scans are __
- Perpendicular to cervical spine
- Parallel to hard palate in chin down position
- Range = neck soft tissue from frontal sinus to line of SC joint
MRI neck sagittal scans are __
- Range = entire neck from frontal sinus to clavicle
- Parallel to cervical spine
- Right to left pinna
MRI neck coronal scans are __
- Perpendicular to nasal septum
- Range = nose tip up to line of spinous process
- Patient must not swallow for sequence acquisition; 30s provided after scan to swallow saliva
where is the target for whole brain scans
glabella
