BRAIN: Spectral CT Flashcards
(18 cards)
What is Spectral CT and how does MonoE imaging enhance visualization?
Spectral CT (also called Dual-Energy CT) uses two different X-ray energy spectra to acquire images simultaneously. This technology allows for:
- Material decomposition - separating different tissue types based on their energy-dependent attenuation
- MonoE (Monoenergetic) imaging - reconstructing images at specific energy levels
- Enhanced vessel definition - MonoE allows visualization of more detailed and extensive arterial networks
Improved contrast resolution - better differentiation between tissues with similar densities - Reduced beam hardening artifacts - particularly useful in brain imaging where bone creates significant artifacts
What are the four main lobes of the brain and their primary functions?
Frontal Lobe
Executive functions, personality, motor control
Contains primary motor cortex (precentral gyrus)
Broca’s area (speech production) in dominant hemisphere
Parietal Lobe
Sensory processing, spatial awareness
Contains primary somatosensory cortex (postcentral gyrus)
Integration of sensory information
Temporal Lobe
Auditory processing, memory formation
Contains hippocampus (memory consolidation)
Wernicke’s area (language comprehension) in dominant hemisphere
Occipital Lobe
Visual processing
Contains primary visual cortex
Visual association areas for complex visual processing
What are the major fissures of the brain and their significance in CT imaging?
Longitudinal Fissure (Interhemispheric Fissure)
Separates left and right cerebral hemispheres
Contains falx cerebri
Important landmark for midline shift assessment
Sylvian Fissure (Lateral Fissure)
Separates temporal lobe from frontal and parietal lobes
Contains middle cerebral artery branches
Critical for stroke assessment - early effacement indicates cerebral edema
Central Sulcus (Rolandic Fissure)
Separates frontal and parietal lobes
Separates motor (precentral) from sensory (postcentral) cortex
Important for functional localization
Define sulci and gyri, and explain their clinical significance in brain CT.
ulci (singular: sulcus)
- Definition: Recesses or grooves on the brain surface
- Function: Increase surface area for cortical neurons
- Types: Primary (deep, consistent), secondary (variable depth), tertiary (shallow)
Gyri (singular: gyrus)
- Definition: Raised portions of cerebral cortex (gray matter)
- Function: Contain neuronal cell bodies and form functional brain regions
- Examples: Precentral gyrus (motor), postcentral gyrus (sensory)
Clinical Significance in CT:
- Sulcal effacement: Indicates cerebral edema or increased intracranial pressure
- Sulcal widening: Suggests cerebral atrophy (aging, dementia, substance abuse)
- Gray-white differentiation: Loss indicates early ischemic changes
- Cortical thickness: Altered in various neurodegenerative conditions
Describe the dura mater and its clinical significance in brain imaging.
Anatomical Properties:
- Outermost and strongest of the three meninges
- Composed of dense fibrous connective tissue
- Very tough and resistant to stretching
- Functions as an anchor system for the brain
Structure:
- Periosteal layer: Adheres to inner skull surface
- Meningeal layer: Forms dural folds (falx cerebri, tentorium cerebelli)
- Dural space: Potential space between layers (site of epidural hematomas)
Clinical Significance:
- Epidural hematoma: Blood accumulation between skull and dura
- Subdural hematoma: Blood between dura and arachnoid
- Dural enhancement: May indicate infection, inflammation, or malignancy
- Dural calcification: Can be seen in elderly patients or certain conditions
What are dural venous sinuses, with focus on the cavernous sinus?
Dural Venous Sinuses Overview:
- Venous channels within dural folds
- Drain venous blood from brain to internal jugular veins
- No valves - bidirectional flow possible
- Major sinuses: Superior sagittal, transverse, sigmoid, cavernous
Cavernous Sinus (Key Focus):
- Location: Lateral to sella turcica
- Contents: Internal carotid artery, cranial nerves III, IV, V1, V2, VI
- Connections:
– Facial vein (via ophthalmic veins)
– Pterygoid venous plexus (via foramina)
Clinical Significance:
- Cavernous sinus thrombosis: Life-threatening condition, often from facial infections
- Carotid-cavernous fistula: Abnormal connection between carotid artery and sinus
- Infections: Can spread from face to brain via venous connections
-Tumors: Pituitary adenomas, meningiomas can involve cavernous sinus
Describe the basal ganglia, their components, and functions.
Definition and Location:
- Group of subcortical gray matter nuclei
- Located in deep aspects of cerebral hemispheres
- Interconnect cerebral cortex, thalamus, and brainstem
Five Pairs of Nuclei:
- Caudate nucleus: C-shaped, adjacent to lateral ventricles
- Putamen: Most lateral component
- Globus pallidus: Medial to putamen (internal and external segments)
- Subthalamic nucleus: Below thalamus
- Substantia nigra: In midbrain
Functions:
- Motor control and movement initiation
- Learning and habit formation
- Reward processing
- Cognitive functions
Clinical Correlations:
- Parkinson’s disease: Substantia nigra dopamine loss
- Huntington’s disease: Caudate nucleus atrophy
- Stroke: Lenticulostriate arteries commonly affected
- Wilson’s disease: Copper deposition in basal ganglia
Detail the putamen’s anatomy, function, and clinical significance.
Anatomical Features:
- Most lateral part of the lentiform nucleus
- Part of the striatum (with caudate nucleus)
- Separated from caudate by internal capsule
- Receives major input from cerebral cortex
Functions:
- Motor control: Fine motor movements and motor planning
- Learning: Procedural learning and habit formation
- Reward processing: Part of brain’s reward circuitry
- Social behaviors: Romance, bonding, and social attachment
Vascular Supply:
- Lenticulostriate arteries (branches of middle cerebral artery)
- Highly susceptible to hypertensive hemorrhage
Common site for lacunar infarcts
Clinical Significance:
- Putaminal hemorrhage: Most common site for hypertensive brain hemorrhage
- Lacunar infarcts: Small vessel disease commonly affects this region
- Movement disorders: Dysfunction leads to dyskinesia, chorea
- Substance abuse: Altered reward processing affects this region
Describe the internal capsule’s anatomy, function, and significance in pathology.
Anatomical Structure:
- Subcortical white matter concentration
- Located in infero-medial portion of each hemisphere
- V-shaped structure with anterior and posterior limbs
- Genu connects the two limbs
Fiber Composition:
- Afferent fibers: Sensory information ascending through thalamus to cortex
- Efferent fibers: Motor commands descending through cerebral peduncles
- Corticospinal tract: Primary motor pathway in posterior limb
- Thalamocortical radiations: Sensory pathways in posterior limb
Clinical Significance:
- Capsular stroke: Small lesion causes major deficits due to fiber concentration
-Tumor invasion: White matter tumors (gliomas) commonly involve internal capsule
- Pure motor hemiparesis: Lesion in posterior limb causes isolated motor weakness
- Surgical planning: Critical structure to preserve during brain surgery
CT Assessment:
- Look for areas of white matter invasion in tumor cases
- Early ischemic changes may show loss of gray-white differentiation
- Hemorrhage in this region causes significant motor deficits
Describe the corpus callosum and its role in brain function.
Anatomical Features:
- Largest white matter commissure in the brain
- Approximately 10 cm in length
- Contains ~200 million nerve fibers
- Four parts: Rostrum, genu, body, splenium
Function:
- Primary pathway for interhemispheric communication
- Allows coordination between left and right brain hemispheres
- Transfers information for bilateral motor coordination
- Essential for complex cognitive tasks requiring bilateral brain cooperation
Clinical Significance:
- Agenesis: Congenital absence, may cause learning disabilities
- Disconnection syndrome: Surgical section leads to split-brain syndrome
- Demyelinating diseases: Multiple sclerosis commonly affects corpus callosum
- Trauma: Diffuse axonal injury often involves corpus callosum
CT/MRI Appearance:
- Well-defined white matter structure on sagittal images
- Thinning may indicate atrophy or developmental abnormalities
- Enhancement may suggest inflammatory or infectious process
- Restricted diffusion in acute injury
Describe the insula’s anatomy, function, and vascular supply significance.
Anatomical Location:
- “Island” of cortex hidden beneath frontal, parietal, and temporal opercula
- Considered by some as the fifth lobe of the brain
- Completely covered by overlying cortex
- Divided into anterior and posterior regions
Functions (Not Fully Understood):
- Interoception: Awareness of internal body states
- Emotion processing: Desires, cravings, disgust
- Neuropsychiatric functions: Addiction, anxiety, depression
- Pain processing: Emotional component of pain perception
- Social cognition: Empathy, social awareness
Critical Vascular Anatomy:
- No collateral circulation: Unique vulnerability
- M2 branches of middle cerebral artery provide sole blood supply
- Poor surgical access: Deep location makes intervention difficult
Clinical Significance:
- Stroke outcome: M2 clots have poor prognosis due to lack of collateral flow
- 70% of cerebral clots occur in middle cerebral artery territory
- Addiction research: Target for understanding substance abuse
- Psychiatric disorders: Implicated in various mental health conditions
Detail the midbrain’s anatomy, functions, and clinical syndromes.
Anatomical Regions:
- Tectum: Roof containing superior and inferior colliculi
- Tegmentum: Floor containing red nucleus, substantia nigra
- Cerebral peduncles: Motor fiber bundles
- Cerebral aqueduct: CSF pathway connecting third and fourth ventricles
Functions:
- Vision: Superior colliculi control eye movements and visual reflexes
- Hearing: Inferior colliculi process auditory information
- Motor control: Substantia nigra produces dopamine for movement
- Arousal: Reticular activating system maintains consciousness
- Temperature regulation: Thermoregulatory centers
Clinical Syndromes (Visible on MRI):
- Parinaud syndrome: Dorsal midbrain lesion, vertical gaze palsy
- Weber syndrome: Ventral midbrain stroke, CN III palsy with hemiparesis
- Claude syndrome: Dorsal midbrain lesion, CN III palsy with ataxia
- Benedikt syndrome: Combined Weber and Claude features
Imaging Significance:
- Small lesions cause major neurological deficits
- Multiple syndromes help localize lesions precisely
- Vascular supply from posterior circulation (basilar artery)
Describe the pons anatomy, connections, and vascular supply.
Anatomical Structure:
- Ventral portion: Contains corticospinal and corticopontine fibers
- Dorsal tegmentum: Contains cranial nerve nuclei and white matter tracts
- Pontocerebellar fibers: Connect cerebral cortex to cerebellum via pons
- Middle cerebellar peduncles: Major output to cerebellum
Key Functions:
- Bridge: Connects cerebrum to cerebellum
- Cranial nerves: Houses nuclei for CN V, VI, VII, VIII
- Motor relay: Corticospinal tract passes through
- Sleep regulation: Contains REM sleep centers
- Respiratory control: Pneumotaxic center
Vascular Supply:
- Basilar artery: Main arterial supply
- Anterior inferior cerebellar artery (AICA)
- Superior cerebellar artery
- Paramedian perforating arteries
Clinical Significance:
- Locked-in syndrome: Ventral pontine lesion spares consciousness but causes quadriplegia
- Facial nerve palsy: CN VII nucleus lesions
- Hearing loss: CN VIII involvement
- Vertigo: Vestibular nucleus dysfunction
Describe the medulla’s anatomy and critical physiological functions.
Anatomical Components:
- Ventral portion: Contains pyramids (motor tracts) and olives
- Dorsal tegmentum: Contains cranial nerve nuclei (CN IX, X, XI, XII)
- Pyramidal decussation: 85% of motor fibers cross here
- Olivary nuclei: Relay stations for cerebellar connections
Critical Functions:
- Vital signs control: Heart rate, blood pressure, breathing
- Relay center: Information transfer between spinal cord and brain
- Cranial nerve functions: Swallowing, speech, tongue movement
- Reflex centers: Cough, sneeze, vomiting reflexes
Vascular Supply:
- Vertebral arteries: Primary blood supply
- Posterior inferior cerebellar artery (PICA)
Anterior spinal artery
Clinical Syndromes:
- Wallenberg syndrome: PICA stroke causing crossed sensory loss
- Medullary compression: Can be fatal due to respiratory center involvement
- Bulbar palsy: Lower motor neuron dysfunction of cranial nerves
- Pseudobulbar palsy: Upper motor neuron dysfunction
Explain the dependency of attenuation on effective atomic number (Zeff) in spectral CT.
Fundamental Principle:
X-ray attenuation depends on the effective atomic number (Zeff) of tissues, which determines which interaction predominates.
Compton Scatter:
- Dominates at lower atomic numbers (soft tissues: muscle, fat, water)
- Energy dependent: Less dependent on atomic number
- Zeff range: Typically <20
- Clinical significance: Provides density information
Photoelectric Effect:
- Dominates at higher atomic numbers (bone, iodine, calcium)
- Highly atomic number dependent (proportional to Z³)
- Energy dependent: Increases dramatically near K-edge energies
- Zeff range: >30-40
Spectral CT Applications:
- Material decomposition: Separates photoelectric from Compton interactions
- Tissue characterization: Distinguishes materials with similar densities but different atomic numbers
- Contrast enhancement: Optimizes iodine visualization using photoelectric dominance
- Artifact reduction: Reduces beam hardening by using appropriate energy levels
What is the K-edge phenomenon and its relevance to spectral CT imaging?
K-Edge Definition:
The K-edge is the binding energy of K-shell electrons in an atom. When X-ray photon energy exceeds this threshold, photoelectric absorption increases dramatically.
Iodine K-Edge:
Energy: 33.2 keV
Significance: Iodine shows maximum photoelectric absorption just above this energy
Clinical relevance: Optimal contrast enhancement occurs near this energy
Physical Explanation:
Below K-edge: Limited photoelectric interaction
At K-edge: Sudden increase in photoelectric absorption
Above K-edge: Maximum photoelectric effect, then gradual decrease
Spectral CT Optimization:
Low energy images (40-70 keV): Enhanced iodine contrast
High energy images (70-140 keV): Reduced iodine effect, better tissue contrast
Material decomposition: Uses K-edge differences to separate materials
Clinical Applications:
Angiography: Enhanced vessel visualization
Perfusion studies: Better contrast-to-noise ratio
Tumor detection: Improved conspicuity of enhancing lesions
Kidney stone analysis: Differentiate stone compositions
Why is 80 kVp optimal for iodine contrast enhancement?
Energy Relationship:
kVp ≠ keV: kVp is maximum possible photon energy, keV is individual photon energy
Effective energy: Approximately 1/3 to 1/2 of kVp setting
80 kVp effective energy: ~35-40 keV
Iodine Optimization at 80 kVp:
Iodine K-edge: 33.2 keV
80 kVp effective energy: 35-40 keV (just above K-edge)
Maximum photoelectric absorption: Occurs just above K-edge energy
Clinical Benefits:
Higher contrast enhancement: Maximum iodine attenuation difference
Stronger signal on iodine maps: Better material decomposition
Better lesion conspicuity: Enhanced visualization of iodine-enhancing lesions
Improved CNR: Better contrast-to-noise ratio for vascular structures
Energy Spectrum Considerations:
120 kVp: Effective energy ~40-60 keV, less optimal for iodine
70 kVp: May not provide sufficient penetration
80 kVp: Optimal balance of penetration and iodine enhancement
Practical Applications:
CT angiography: Enhanced vessel visualization
Brain perfusion: Better tissue enhancement detection
Tumor imaging: Improved enhancement pattern analysis
Summarize the key clinical applications of spectral CT in brain imaging.
Material Decomposition Applications:
1. Iodine mapping: Quantitative contrast enhancement analysis
2. Calcium removal: Better visualization of contrast-enhanced vessels
3. Hemorrhage characterization: Distinguish acute blood from iodine
4. Edema assessment: Differentiate vasogenic from cytotoxic edema
Monoenergetic Imaging Benefits:
- Low keV (40-70): Enhanced contrast, improved small vessel visualization
- High keV (70-140): Reduced artifacts, better visualization through bone
- Optimal CNR: Customizable for specific diagnostic tasks
Clinical Scenarios:
Stroke imaging:
- Enhanced detection of small vessel occlusions
- Better perfusion parameter accuracy
- Improved hemorrhage vs. contrast differentiation
Tumor imaging:
- Quantitative enhancement analysis
- Better differentiation of tumor from edema
- Improved surgical planning
Vascular imaging:
- Enhanced small vessel visualization
- Reduced streak artifacts from dense contrast
- Better evaluation of vessel patency
Trauma:
- Distinguish traumatic hemorrhage from contrast extravasation
- Better evaluation of vascular injury
Reduced metal artifacts
