Head, Neck, and Spinal Column Imaging Flashcards
MR imaging is dependent on the biologically changeable parameters of the:
Proton density (PD)
Longitudinal relaxation time (T1)
Transverse relaxation time (T2)
What can pulse sequences characterize?
Chemical and physical structures of a pathology over time
What is an additional method to more accurately define lesions?
Multiplanar imaging
What are flow-sensitive pulse sequences and MR angiography used to show?
Vascular structures and their blood flow
How is brain function investigated using MR?
By having the patient perform mental tasks. Any changes are noted in the regional cerebral blood flow and oxygenation level (for example, have the patient stare at a specific spot: occipital lobe will have increased blood flow)
Which imaging sequences are used to demonstrate cerebral infarcts?
Diffusion weighted imaging sequences (DWI). Areas of restricted diffusion are highlighted during post-processing techniques
What type of imaging is used to determine axonal pathways connecting functional areas in the brain?
Diffusion tensor imaging
What information does MR spectroscopy provide?
The biochemistry and metabolism of tissue
How are catastrophes avoided in the magnet room?
With proper screening of patients, equipment, and personnel for ferromagnetic materials, pacemakers, and other MR incompatible devices
What are the clinical indications for brain imaging?
Multiple sclerosis and other white matter diseases such as encephalitis and herpes
Primary tumour assessment/metastatic disease
AIDS (toxoplasmosis)
Infarction (TIA vs. CVA)
Hemorrhage
Hearing loss
Visual disturbances
Infection
Trauma
Unexplained neurological symptoms/deficits
Preoperative planning
Temporal lobe epilepsy, non-hemorrhagic brain contusions, and traumatic shear injuries are also seen in the early stages
What does pituitary gland (sella turcica) imaging show?
Flow of contrast in and out of the pituitary gland
Multiplanar imaging of paediatric anatomy gives important information about:
The corpus callous and posterior fossa structures
The superior gray/white matter contrast allows accurate assessment of:
Myelination and cortical abnormalities
Blood flow voids within arteries are shown with which sequences?
Spin-echo imaging sequences
MR angiography is used to demonstrate which pathologies?
Vascular stenosis, occlusions, aneurysms, AVMS, as well as cavernous angiomas
Which pulse sequence is the gold standard for imaging of the central nervous system?
Conventional spin-echo. It produces good tissue contrast and has a high sensitivity for abnormalities. Often used in paediatric imaging
Advantages of FSE sequences
Reduces scan time, most sensitive for detecting brain pathology
Which brain pathology is PD imaging mostly used for?
Multiple sclerosis
What are the minimum and maximum number of coils/channels for a head coil?
2 and 32
What is a transceiver?
Both transmits and receives RF pulses. Quadrature coils (volume coil). Uses two coils to transmit a signal to the patient as well as receive a signal back from the patient. Obtains a uniform signal across the entire FOV
How many component are the 1.5T and 3.0T HNS coils composed of?
5 separate components labeled A to E
How many elements are there in the 1.5T and 3.0T HNS coils?
29
What are HNS coils designed to do?
To eliminate multiple coil usage per patient in order to increase throughput and patient comfort
What is the patient position for a routine brain procedure?
Supine, head in the head coil with shoulders usually resting against the lower margin of the head holder
How should the IPL be aligned for brain imaging?
Parallel to the couch
What is the landmark for routine brain imaging?
The nasion
What alternate position can be used for brain imaging if the patient condition doesn’t allow for a supine?
A lateral decubitus position
What does it mean for the patient positioning to be isocenter?
All three planes are aligned
Routine brain slice prescription:
Axial sequence: programmed off the sagittal localizer
Sagittal and coronal sequences programmed off the axial localizer
What is the typical adult FOV for brain imaging?
23cm
What is the slice thickness/spacing for routine brain?
Medium slices/gap
5-6mm/2mm
(5mm is more common)
Routine brain: Sagittal/sagittal oblique
May have to angle slices to compensate for rotation
Scan left to right
Include temporal lobes and area from foramen magnum to the top of the skull
What are the first and last slices for a sagittal routine brain?
First: left lateral temporal lobe
Last: right lateral temporal lobe
Routine brain: Axial/ axial oblique
May have to angle slices to compensate for rotation
Scan inferior to superior
Include foramen magnum to superior brain. Include all brain surface and soft tissue laterally. Always have the spinal cord.
Angle to the anterior-posterior commissure axis
Routine brain: Coronal/coronal oblique
May have to angle slices to compensate for rotation
Scan posterior to anterior
Include cerebellum to frontal lobe. Include spinal cord inferiorly and parietal bones superiorly
What are the first and last slices for an axial routine brain?
First: foramen magnum
Last: superior brain surface
What are the first and last slices for a coronal routine brain?
First: posterior cerebellum
Last: frontal lobe
Do thinner slices increase or decrease scan time?
Increase
What is the typical scan time for a sequence for routine brain?
2-4 minutes
What resolution is used for imaging smaller organs in the brain?
High-resolution imaging. Smaller slice thickness
Larger (fine) matrix (small pixels)
Reduction in the total number of slices for the specific anatomy
What is the patient position for temporal lobes?
Supine, head in head coil, shoulders at inferior margin of it, IPL parallel to couch
What is the landmark for temporal lobes?
At the nasion
What are the clinical indications for temporal lobes?
Lesions, vascular malformations
Leukodystrophies, atrophic processes
Temporal lobe epilepsy
Hippocambus changes
What is the most common clinical indication for temporal lobes?
Temporal lobe epilepsy
When scanning temporal lobes, what do changes in the hippocampus indicate?
Alzheimer’s disease
What do we try and angle to for temporal lobes?
Parallel to the hippocampus
Temporal lobes: Sagittal T1 - whole brain
This will provide a data set for the remaining pulse sequences
Medium slices/gap: 5-6mm
Left to right throughout the whole head
Include the area from the foramen magnum to the top of the head (FOV)
Temporal lobes: Axial Oblique FSE T2
Thin slices/gap: 2-4mm
Improves spatial resolution
Angled parallel to the temporal lobes
Scan inferior to superior from the inferior aspect of the temporal lobes to the superior border of the body of the corpus callosum
Occipital to frontal lobes are included in the FOV
Temporal lobes: Coronal Oblique FSE T1
Thin slices/gap: 2-4mm
Increases spatial resolution
From posterior cerebellum to anterior border of the genu of the corpus callosum
Angled parallel to axial slices (textbook)
Angled perpendicular to the Sylvian fissure (clinical)
What is the most important imaging sequence/plane for hippocampal disease?
Coronal Oblique FSE T1
Temporal lobes: 3D coronal GRE T1 (Spoiled)
Shows small tumours in the temporal lobes (volume imaging provides thin slices with no gaps)
Medium number of slices (64)
Sequence is often used for post-gadolinium studies
Images can be reformatted in all three imaging planes
What are inversion recovery (IR) pulse sequences used to show?
A specific tissue type - can be T1 or T2 weighted
IR provides images that can null (saturate) a specific tissue
What is IR timing based on?
The recovery time of the tissue being nulled
Why are IR sequences used for imaging temporal lobes?
Since white matter disease can be subtle, eliminating the normal white matter tissue will help demonstrate a small temporal lobe lesion. Signal will be nulled from white matter if we use an inversion time of around 300ms
What are common artifacts when imaging temporal lobes?
Flow from carotid and vertebral arteries
Magnetic susceptibility on the coronal T1 spoiled GRE
What are some remedies for magnetic susceptibility artifact? (temporal lobes)
Cannot remove petrous ridges, use SE sequences
Decrease TE
Increase bandwidth
What are some remedies for flow artifacts? (temporal lobes)
Spatial presaturation pulses inferior to the FOV
Gradient moment nulling (GMN) (increases minimum TE time - reserved for T2 W imaging as this pulse sequence has along TR time)
What are some clinical indications for the IAC/posterior fossa?
Acoustic neuromas - vertigo, hearing loss, and tinnitus are symptoms Numbness in the face Posterior fossa lesion Hemi facial spasm Trigeminal neuralgia
IAC/Posterior fossa: Sagittal T1 or GRE T2*
Can be bilateral or unilateral imaging Most common is bilateral Thin slices/gap: 2-4mm From left to right through the IAC Medial to lateral from the foramen magnum to the superior border of the body of the corpus callosum in the FOV
IAC/Posterior fossa: Coronal T1
Demonstrates the IAC well
Posterior cerebellum to the clivus
Thin slices/gap: 2-4mm
Angle parallel to the IAC
IAC/Posterior fossa: Axial or Axial Oblique FSE T2
Thin slices/gap: 2-4mm, 3mm
Fin matrix 512x512 with small FOV
Inferior to superior from foramen magnum to the superior border of the petrous ridges
Slices angled parallel to direct both IAC
IAC/Posterior fossa: Axial 3D FSE T2 or T2* GRE
High contrast images are produced Increased SNR No gap Isotropic Small (32) to medium (64) number of slices for volume
Which imaging planes are best to demonstrate the IAC?
Axial and coronal
What are some imaging characteristics of the IAC?
Inherent tissue contrast between CSF and nerves
CSF bright on T2, nerves hypointense on T1 and T2
T2 W images are often used, negate the need for gadolinium
NEX/NSA usually increased due to fine matrix to increase SNR
What is the artifact when imaging IAC/posterior fossa?
Flow from venous sinuses if including the posterior fossa in imaging
What is the remedy for flow artifact? (IAC/posterior fossa)
GMN (increases minimum TE)
Spatial presaturation bands S and I (saturates venous flow)
Peripheral gating in extreme cases of severe flow artifacts
What imaging sequences are used to image the temporal lobes?
Sagittal T1 (Whole brain) Axial oblique FSE T2 Coronal oblique FSE T1 3D Coronal GRE T1 (spoiled) IR
What are the imaging sequences used to image the IAC/posterior fossa?
Sagittal T1 or GRE T2*
Coronal T1
Axial/axial oblique FSE T2
Axial 3D FSE T2 or T2* GRE
What are some clinical indications for trigeminal neuralgia?
Trigeminal neuralgia facial pain/spasm Vascular compression Lesions Trigeminal schwannoma/neuroma Neurofibromatosis
What are the imaging sequences used for trigeminal neuralgia?
Axial oblique
Axial volume imaging
Coronal FSE T1/T2
Trigeminal neuralgia: Axial oblique
Thin slices/gap
Slices programmed inferior to superior from foramen magnum to tectum (clinically to the orbits, some sites request to include C3 inferiorly)
Angled perpendicular to the brain stem
Trigeminal neuralgia: axial volume imaging
Programmed straight
Reconstruct using oblique angles
Thin slices/no gaps
Fine/large matrix
Trigeminal neuralgia: coronal FSE T1/T2
Medium slices/gap
From posterior to anterior from pons to anterior face
Include sinuses and mandible
Angled parallel to the brainstem
What are some clinical indications for the pituitary fossa/sella?
Abnormal pituitary gland functions (hyperprolactinemia, Cushing’s disease, acromegaly, hypopituitarism, diabetes insipidus, amenorrhea)
Hypothalamic disorders
Visual field defects
Pre and postoperative follow up pituitary adenomas
What imaging sequences are used to image the pituitary fossa/sella?
Sagittal T1
Coronal FSE T1
Post-contrast studies
Pituitary Fossa/Sella: sagittal T1
Thin slices/gap
Left to right to include lateral borders of the pituitary fossa, include inferior edge of the sphenoid sinus to the superior portion of the lateral ventricles
Angled parallel to the falx cerebri (angled off the coronal)
Pituitary Fossa/Sella: Coronal FSE T1
Thin slices/gap: interleaved
From posterior clinoids to anterior clinoids
Include the border of the sphenoid sinus to the superior portion of the lateral ventricles
Angle slices perpendicular to the floor of the sella (if programmed off sagittal)
Angle slices perpendicular to the midline of the brain (if programmed off axial)
What are pituitary post-contrast studies?
Dynamic scanning - coronal
Timed sequences
Microadenomas are difficult to demonstrate
Spoiled GRE T1 sequences are performed due to faster scanning
Half dose of gadolinium
Why is timing of scans important for pituitary post contrast studies?
Because both pituitary gland and microadenomas enhance
30, 60, 90, 120, 180 seconds
Which enhances first in post contrast studies, the pituitary gland or a microadenoma?
The pituitary gland
What are some artifacts when imaging the pituitary fossa/sella?
Flow from COW
Aliasing/wrap from small FOV
What is the remedy for flow artifact? (Sella)
Spatial presaturation bands S and I; R and L may be used
What are the remedies for aliasing? (Sella)
Apply oversampling techniques
Increase FOV
What are the clinical indications for orbits?
Proptosis
Visual disturbances
Evaluation of orbital or ocular lesions
Which alignment light passes through the orbits for orbital imaging?
The horizontal alignment light