, Mark Gorman2 and Salman Al Jerdi2
(1)
Department of Cardiovascular Medicine and Electrophysiology, Yale School of Medicine, Yale-New Haven Hospital, New Haven, CT, USA
(2)
Department of Cardiovascular Medicine, Yale School of Medicine, Yale-New Haven Hospital, New Haven, CT, USA
Abbreviations
ADC
Apparent diffusion coefficient
ASPECTS
Alberta Stroke Program Early CT score
CBF
Cerebral blood flow
CBV
Cerebral blood volume
CCA
Common carotid artery
CSF
Cerebrospinal fluid
CT
Computed tomography
CTA
Computed tomography angiography
DWI
Diffusion-weighted imaging
ECST
European Carotid Surgery Trial
EDV
End-diastolic velocity
FLAIR
Fluid-attenuated inversion recovery
HU
Hounsfield unit
ICA
Internal carotid artery
IMT
Intimal medial thickness
MCA
Middle cerebral artery
MFV
Mean flow velocity
MI
Myocardial infarction
MIP
Maximum intensity projection
MRA
Magnetic resonance angiography
MRI
Magnetic resonance imaging
MTT
Mean transit time
NASCET
North American Symptomatic Carotid Endarterectomy Trial
PCA
Posterior cerebral artery
PSV
Peak systolic velocity
SAH
Subarachnoid hemorrhage
TCD
Transcranial Doppler
TEE
Transesophageal echo
TPA
Tissue plasminogen activator
Introduction
While the boards do not test the nitty-gritty details on imaging modalities, you will be expected to identify abnormal features on head and vessel imaging. Familiarizing yourself with the various imaging techniques (CT, MRI, angiography, and ultrasound) will not only prepare you for the boards but allow you to rapidly review and interpret these studies independently, in real time, to guide management.
Computed Tomography (CT)
Computed Tomography (CT): uses X-rays to create cross-sectional images
Typically used in the initial screening for acute stroke
Noncontrast CT useful to exclude acute hemorrhage
Advantages:
Rapid
Noninvasive
Widespread, inexpensive
No need to screen for metal
High sensitivity for acute hemorrhage
Cheaper than MRI
Disadvantages:
Exposes patients to ionizing radiation
Poor visualization of posterior fossa
Low sensitivity for early stroke
Focal hypodensity can be seen on noncontrast CT within 3–6 h of symptom onset
Dark on CT: CSF, water, air, fat
Bright on CT: Blood, calcium, bone, contrast
CT Perfusion
Helps characterize tissue-level blood flow
Cerebral Blood Flow (CBF ): volume of blood moving through a given unit of brain tissue per unit time. Detects hypoperfused tissue
Cerebral Blood Volume (CBV ): total volume of blood in a given unit volume of brain tissue. Highly specific for critical hypoperfusion, less sensitive for mild/moderate hypoperfusion
Mean Transit Time (MTT ): average transit time of blood through a given region of brain tissue
MTT = CBV /CBF
Uses iodinated contrast
Patients with allergy/anaphylaxis may need pretreatment with diphenhydramine and steroids
Factors that may increase risk of contrast-induced nephropathy
Dehydration
Baseline chronic kidney disease
Diabetes
Metformin use – risk of lactic acidosis
Paraproteinemias
Hounsfield Units (HU): measure density of structures on CT imaging
Air: −1000 HU
Fat: −100 to −50 HU
Water: 0 HU
CSF: 15 HU
White matter: 20–30 HU
Blood: 40–100 HU
Gray matter: 37–45 HU
Bone: 400–3000 HU
ASPECTS Score (Figs. 16-1 and 16-2)
Figure 16-1
Structures included in Aspects Score: C caudate, IC internal capsule, L lentiform nucleus, I insula, M1, M2, M3, and superior MCA territories (M4, M5, M6) (Images courtesy of Dr. Ajay Malhotra)
Figure 16-2
Right MCA stroke. CT images (top left, right) showing hypodensity in right insula (ASPECTS score = 9). DWI and ADC sequences (bottom left and right respectively) showing hyperintense and hypointense signals in right insula, suggesting acute stroke (Images courtesy of Dr. Ajay Malhotra)
Alberta Stroke Program Early CT Score: reproducible weighted volumetric grading system to assess early ischemic changes on head CT; may be used to identify patients unlikely to make independent recovery, and guide treatment with tPARelated posts:
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