Radiographic Studies

Plain X-rays

Skull
Spine
Shunt Series – used in evaluating shunt dysfunction; includes AP/lateral skull, chest x-ray, abdominal scan

Ultrasound

Useful in neonatal intracranial imaging (diagnosis of hydrocephalus, IVH), myelodysplasia, intra-op lesion localization, abdominal shunt evaluation
Intrauterine US can reveal myelodysplasia or encephalocele prior to child's birth
Advantages – Portable; images CSF, hemorrhage, and edema; able to evaluate blood flow
Limitations – Restricted field of view, suboptimal tissue definition

Carotid duplex

Ultrasound study; often initial study in evaluation of carotid stenosis

Transcranial Doppler (TCD)

Ultrasound study; used in evaluation of intracranial carotid flow to rule out vasospasm in SAH patients

CT (computed tomography)

Most rapidly available study to rule out intracranial lesion
Displays bone, hemorrhage, and calcification better than MRI
Houndsfield Units:

>90 = bone
<90 = blood

Special Studies:

Bone Windows – Display bone best
Coronal Study – Able to image sella and orbits. Patient must be able to hyperextend neck to obtain.
Sagittal Reconstructions – Thin axial images are reformatted. Useful with spinal fractures.
Posterior Fossa Cuts – Thin sections through posterior fossa. Improves resolution and decreases bone artifact.
3-D Reconstructions – Thin axial sections are reformatted. Useful in planning craniofacial procedures.

Contrasted studies are iodinated media which can cause contrast reaction
Appearance on CT:

Hyperdense – (Increased attenuation, bright): acute hemorrhage, calcium, bone, contrast agent
Isodense – Brain parenchyma, subacute hematoma
Hypodense – (Decreased attenuation, dark): CSF, air, fat, chronic hematoma, infarction, edema

Advantages – Short study time; images hemorrhage, skull, and parenchyma; no limitation in patients with paramagnetic implants
Limitations – Bone artifact, inconsistent posterior fossa definition, suboptimal white matter definition

MRI (magnetic resonance imaging)

Better resolution than CT imaging, especially with posterior fossa, pituitary, and spine imaging
Provides imaging in multiple planes (axial, sagittal, coronal)
Contraindicated in patients with pacemakers, aneurysm clips, or metallic foreign bodies
Contrasted studies use gadolinium, a paramagnetic agent, and contrast reactions are rare
Appearance on MRI:

T1 weighted images (Short TR/Short TE)

Increased signal intensity (Bright): Hyperacute/subacute hemorrhage, gadolinium, fat, methemoglobin, iron
Decreased signal intensity (Dark): Hemosiderin, calcium, infarction, CSF, chronic hemorrhage

T2 weighted images (Long TR/Long TE)

Increased signal intensity (Bright): Hyperacute/subacute hemorrhage, edema, CSF
Decreased signal intensity (Dark): Hemosiderin, flow voids, methemoglobin, deoxyhemoglobin, fat, iron

Advantages – No bone artifact; better definition of parenchymas, hemorrhage, and vasculature; able to age hemorrhage; more predictive of outcome
Limitations – Length of study, suboptimal definition of SAH, unable to image patients with paramagnetic implants
magnetic field aligns 50% of electrons in water; electrons hit by radiofrequency; as electrons realign with field, energy is released
Sequences

Inversion revocery (e.g FLAIR) – increases grey-white differentiation; CSF signal nullified- shows edema
Diffusion – shows movement of water/fluid

Ischemia – swelling decreases extracellular space, decreasing extracellular diffusion (appears hyperintense on DWI)
recovery phase – diffusion increases due to loss of cell wall integrity (appears hypointense)
Can also be used to differentiate abscess (hyperdense since swollen cells prevent diffusion) vs. tumor (hypodense because of free diffusion through necrosis)

Intracerebral Hemorrhage

Time	Contents	T1	T2
Hyperacute (4-6hrs)	oxyhemaglobin	iso	hyper
Acute (7-72 hrs)	deoxyhemaglobin	iso/hypo	hypo center hyper edge
Early subacute (4-7 days)	intracellular methemaglobin	hyper center hypo edge	hypo
Late subacute (1-4 weeks)	extracellular methemaglobin	hyper	hyper
Early Chronic (months)		hypo/iso edge hyper center	hypo edge hyper center
Chronic		hypo	hyper

MR spectroscopy

Signals from organic molecules

Chemical	Function	Significance
Myoinositol	Sugar phosphate	sugar metabolism
Choline	membrane turnover	increased with tumors, gliosis (as in seizures)
Creatine and phosphocreatine	Energy pool	increased with gliosis
Glutamate and glutamine	neurotransmitter and metabolite
NAA (N-acetyl aspartate)	Key indicator of neuronal health	decreased with tumors
Lactate	product of anaerobic metabolism	indicates ischemia

Functional MRI

Measures change in the ratio of intravascular oxyhemaglobin to deoxyhemaglobin
Shows changes in oxygen extraction fraction
Bright signal due to increased blood flow ending up in veins

increased flow results in decreased extraction

MRA/MRV (magnetic resonance angiography/venography)

Allows imaging of vasculature without invasive risks of angiography, though resolution remains its main limitation

PET (positron emission tomography) – Performed in CT scanner

fluorodeoxyglucose (FDG)

FDG increased in high-grade tumors, PML, lymphoma, fungal abscess, active seizure
FDG decreased in low-grade tumors, abscess, epileptogenic focus between seizures

15-oxygen

regional cerebral blood flow- semiquantitative study

inject and wait 30-60 seconds

regional cerebral blood volume- more quantitative study

inject then get dynamic images
can calculate CMRO2 for oxygen extraction

Misery perfusion syndrome

seen in ischemic penumbra
decreased rCBF with normal CMRO2

Mainly experimental, but commonly used in patients with ischemic brain disease
Provides a quantitative assessment of cerebral blood flow
Only test to determine fractional oxygen extraction ratio in patients with cerebral ischemia. May be useful in selecting patients for bypass.

SPECT (single proton emission computed tomography) – uses technicium-99

99M TcHMPAO SPECT- measures blood flow (can perform balloon occlusion test)
Seizures- increases with active seizure (normal or decreased intraictally)
99M TcHMPAO-labelled leukocytes- tagged WBC scan
Non-quantitative method of assessing cerebral blood flow

Bone scan

Useful in looking for metastasis to spine, and evaluating infection

Nuclear perfusion scan

Used in documentation of brain death

Myelography

Indications include diagnosis of spinal disease (especially in patients unable to undergo MRI)
Complications include those of LP, contrast reactions, arachnoiditis, meningitis
Post-procedure CT (and possible delayed CT) are essential

Cisternography

Injection of radio-isotope or contrast into intrathecal space with follow-up imaging
Commonly used in localizing CSF leaks, diagnosis NPH
Complications include those of LP, meningitis, contrast reactions

Ventriculography

Injection of contrast material into the ventricular system via a ventricular catheter
Rarely performed since onset of CT and MRI imaging
Occasionally used to R/O intraventricular cyst or trapped ventricle

Cerebral Angiography

Uses include the diagnosis of carotid disease, vascular malformations, aneurysms, and to define vascular supply to intracranial lesions
Complications include contrast reactions, arterial intimal tear, puncture site hematoma, cerebral infarct, and neurologic deficit (temporary or permanent)