CT and MR angiography Flashcards
Where does the vertebral arteries run up through?
Transverse foramina of the cervical vertebrae and up through the foramen magnum
What branch does vertebral arteries give rise to?
Posterior Inferior Cerebellar Arteries (PICA)
and anterior spinal arteries
What branch does PICA give rise to?
Posterior spinal arteries
When vertebral arteries come together and fuse what will it form?
Basilar arteries
What branches does basilar arteries give rise to?
Anterior Inferior Cerebellar arteries at the level of pons
and pontine branches
What supplies the top of the cerebellum?
Superior Cerebellar Arteries
What does basilar arteries feed into?
Posterior part of Circle of Willis: Posterior cerebral arteries
What are the branches within the middle cerebral arteries?
Anterior choroidal artery
What are arteries that goes to the lentiform nucleus?
Lenticulostriate arteries
What is found within the optic chiasm?
Anterior communicating artery
What is the venous system?
Part of circulation in which the blood is transported from periphery back to the heart
What are dural sinuses?
Veins found within space between periosteal layer and meningeal layer of dura mater
Where is the inferior sagittal sinus located within?
lower part of the falx cerebri
What is the superior sagittal sinus?
Unpaired area along the attached margin of the falx cerebri
Where will the inferior sagittal sinus empty into?
sagittal sinus
Where is opthalmic vein located in?
orbital cavity and facial vein drain into the cavernous sinus
What two branches does cavernous sinus give off?
- Superior petrosal sinus
2. Inferior petrosal sinus
Where does the sigmoid sinus empty into?
Internal Jugular vein
What does the clinical indications include?
- Ischemic stroke
- Transient Ischemic attack
- Subarachnoid haemorrhage
- Cerebral parenchymal haemorrhage
What are examples of ischemic stroke?
Detect occlusion, thrombus, dissection and collaterals
What is an example of TIA?
Carotid artery stenosis
What is an example of subarachnoid haemorrhage?
Aneurysms
What is example of cerebral parenchymal hemorrhage?
Vascular malformation
What is CT angiography technique?
Uses injection of contrast material into blood vessels and CT scanning to help diagnosis and evaluate blood vessel disease
What do angiography exams produce?
Pictures of major blood vessels throughout body
What does CTA combine?
CT scan with injection of dye
What are characteristics of CT angiography?
- Helical CT acquisition
- IV injection of iodinated contrast
- Dose, weight, number of detectors
- Timing: Fixed scan delay, test bolus injection, automated bolus tracking
- Administration rate
What are the clinical use of CTA?
- Fast diagnosis of major vessel occlusion
- Fast diagnosis of presence of aneurysm
- Screening of carotid stenosis
What are the CTA post-processing?
- Axial source data
- Isotropic voxels
- Multiplanar reformats
- Maximum intensity projections
- 3D volume rendering
- Curved planar reformats
What is multiplanar reformats?
- Axial/coronal/sagittal
2. Thickness
What is maximum intensity projections?
Projecting the voxel with the highest attenuation value on every view throughout the volume onto 2D image
What is 3D volume rendering?
3D volume reconstruction method that allows every voxel in the volume data to contribute to the reconstructed image
What is Magnetic Resonance Angiography (MRA)?
Uses powerful magnetic field, radiowaves and computer to evaluate blood vessels and help identify abnormalities
does not use radiation
MRA contrast material
less likely to cause an allergic reaction
What are the MRA techniques?
- Time of Flight (TOF)
- Contrast enhanced (CEMRA)
- Phase contrast (PC)
- Other: ASL MR angiography
What is TOF?
Measuring distance between a sensor and an object based on time difference between emission of signal and its reutn to the sensor after being reflected by an object
What is CEMRA?
- Gadolinium-based agent is injected
2. Inject a compact bolus of contrast into central circulation with clearing all contrast from proximal veins
What is phase contrast?
- Looking at both positive and negative velocities
2. Visualise moving fluid
What is MRA TOF?
- Technique to visualise flow within vessels without the need for contrast
- 2D or 3D Gradient Echo sequence
- Based on flow related enhancement on imaging slice
- Manipulates MR environment so only spins within flowing blood generates signal
- Stationary spins saturated – low MR signal
- Fresh unsaturated spins carried in by flowing blood
What is TOF principles?
- Radiofrequency pulses suppress slice
- Flowing blood not suppressed
- Slice perpendicular to the flow
- Saturation pulse – saturate blood from distal – doesn’t corrupt the images, if flow is too slow – suppression occurs
Saturation of MRA TOF?
- Background tissue suppression
- Blood in slice taking too long (disadvantage)
- Worse with thick slabs
Intravoxel dephasing of MRA TOF?
- Different velocities within voxel – turbulent flow, stenosis, corners
- Susceptibility induced – field inhomogeneities, transitions e.g. skull base
- Worse with big voxels
What is the main use of CEMRA?
Extracanial MRA
What are the characteristics of CEMRA?
- 3D spoiled gradient echo sequence
- Flip angle: 25-50 degrees
- Gadolinium injection - shorten T1
- Blood high signal
- Rapid acquisition
- Arterial phase - timing of acquisition is important
- synchronised with first pass
- Images in long axis of vessel e.g. cornonal
- not reliant on inflow or new spins
- more efficient data acquisition
- substraction
What is the main use of MRA phase contrast?
- Visualise moving fluids,
2. MRV
What are the characteristics of MRA phase contrast?
- No contrast required
- Spins passing along the direction of the magnetic field gradient acquire phase change
- Measures phase change
- Proportional to distance travelled along gradient (i.e. velocity)
- Provide quantitate and directional data
What is Arterial Spin labelling
- Flowing blood is tagged with RF-Pulses to have high magnetization, whilst stationary tissue is suppressed
- Assess cerebral vasculature and hemodynamics
- Conditions exhibiting delayed arterial transit time and collateral flow pathways
What are the advantages of CTA?
- Availibility of MDCT
- Rapid: limits motion artefact
- Patient tolerance
- No flow related artefacts
- calcification well seen
- Wide range of reformations
- Whole head and neck circulation
- Imaging of non-vascular structures
What are the limitations of CTA?
- Ionizing radiation
- Iodinated contrast
- Streak artefacts
- Lower resolution
- Acquisition limit evaluation of flow
What are consequence of iodinated contrast?
- Invasive
- Reactions
- Acute kidney injury at risk patients
What are examples of streak artefacts?
- Dental amalgam
- Metallic implants
- Dense contrast
What is consequence of lower resolution?
Difficulty evaluating subtle well changes e.g. vasculitis
What are the pitfalls of CTA?
- windowing
- Suboptimal opacification
- Vessel segment hidden by bone at skull base
- Over zealous post processing
What are the advantages of MR ?
- No ionizing radiation
- Combined with other sequences
- Post-processing
What are the limitations of MR?
• Susceptible to artefacts • Long acquisition times • Patient compliance – claustrophobia • MR safety - Pacemakers, certain implants, aneurysm clips • Physics support • Expensive
What are advantages of 2D TOF?
• Individual slices - Minimal saturation of blood - Coverage expandable by adding more slices • Sensitivity to slow flow • Sat band prior to each slice - Good venous saturation
What are disadvantages of 2D TOF?
- Large voxels, Long TE intravoxel dephasing
- Relatively poor resolution
- Poor suppression of short T1 tissues
What are advantages of 3D TOF?
- High spatial resolution
- Small voxel – minimises intravoxel dephasing
- Short TE (less dephasing)
- High SNR (3D)
- Isotropic voxels – Multiplanar Reformations
What are disadvantages of 3D TOF?
- Slab saturation – slab boundary artefact
- Less effective venous suppression
- Poor suppression of short T1 tissues
- Motion artefact corrupt all slices
- Slightly longer acquisition than 2D
What are advantages of CEMRA?
- Low intravoxel dephasing – short TR
- Low saturation – Gadolinium
- Short acquisition – low motion
- Less Artefacts
What are disadvantages of CEMRA?
- Gadolinium
- Cannot be repeated
- Synchronisation
- Short acquisition – resolution challenge
- Subtraction – reduced SNR
What are advantages of ASL MRA?
- Covers entire vasculature
- Non-invasive
- No contrast agents
- No ionizing radiation
- Vessel selection
- Can be quantitative
What are the artefact of ASL MRA?
- Require high arterial velocities
- Presumes the flow direction is known, which is not always the case
- Potential partial labeling of vessels in close proximity to selected vessel
- Small signal variations within vessels affect assessment of partial stenosis
