Study guide
CT Perfusion & Advanced Perfusion Imaging
ABPN Neurocritical Care Study Guide Exam
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1 Chapter 1: Neurologic Examination & Coma Assessment in the ICU
Current Examination, Blueprint & Preparation Neurologic Examination in Critically Ill Patients Coma Evaluation & Consciousness Alterations Delirium & Toxic-Metabolic Encephalopathy in the ICU
2 Chapter 2: Cerebral Physiology & Intracranial Dynamics
Cerebral Blood Flow, Metabolism & Autoregulation Intracranial Pressure & Compliance Cerebral Edema & Herniation Syndromes
3 Chapter 3: Intracranial Hypertension & Cerebral Perfusion Management
Tiered ICP Management Protocols Hyperosmolar Therapy & Fluid Management Advanced & Refractory ICP Interventions
4 Chapter 4: Airway, Mechanical Ventilation & Pulmonary ICU Management
Emergency Airway Management & Neuro-Intubation Mechanical Ventilation Strategies in Acute Brain Injury Tracheostomy & Ventilator Weaning in Neurocritical Care Pulmonary Complications in the Neuro-ICU Obstructive Lung Disease, Pulmonary Hypertension & Bronchoscopy
5 Chapter 5: Hemodynamics, Shock & Cardiovascular Management
Hemodynamic Monitoring & Blood Pressure Targets Vasoactive Agents: Inotropes, Vasopressors & Antihypertensives Cardiac Complications of Brain Injury
6 Chapter 6: Neuropharmacology, Analgesia & Sedation
ICU Sedation & Analgesia Neuromuscular Blockade & Monitoring Propofol Infusion Syndrome & Drug Toxicities Antiseizure Drug Pharmacology in the ICU
7 Bleeding, Thrombosis & Hematologic Emergencies
Warfarin & Heparin Reversal Direct Oral Anticoagulant (DOAC) Reversal Antiplatelet Management & Platelet Dysfunction Venous Thromboembolism Prophylaxis & Management Transfusion, Coagulopathy, TMA & Cellular-Therapy Neurotoxicity
8 Chapter 8: Systemic ICU Care, Fluids, Electrolytes & Endocrine
Hyponatremia & Osmoregulation: SIADH vs Cerebral Salt Wasting Diabetes Insipidus, Hypernatremia & Endocrine Crises Critical Care Prophylaxis, Nutrition & Infection Prevention
9 Systemic Trauma & Environmental Injury
Polytrauma, Chest Injury & Abdominal Hemorrhage Burns, Electrical Injury & Hanging
10 Cardiac Emergencies & Mechanical Support
IABP, Ventricular Devices & ECMO Acute Coronary, Valvular, Rhythm & Aortic Emergencies
11 Kidney Injury, Acid–Base & Renal Replacement
Acute Kidney Injury & Renal Drug Clearance Acid–Base Disorders, Electrolytes & Renal Replacement
12 Systemic Infection & Endocrine Emergencies
Sepsis, Endocarditis & Antimicrobial Principles Thyroid, Adrenal & Dysglycemic Emergencies
13 Gastrointestinal & Hepatic Emergencies
Acute Abdomen, GI Bleeding & Abdominal Compartment Syndrome Acute Liver Failure, Cirrhosis & Hepatic Drug Effects
14 Chapter 9: Neuroimaging in the Neuro-ICU
Non-Contrast CT & CT Angiography CT Perfusion & Advanced Perfusion Imaging Magnetic Resonance Imaging in Critical Illness
15 Chapter 10: Electrophysiology & Neuromonitoring
Continuous EEG & ACNS Standardized Critical Care Terminology Invasive Neuromonitoring: ICP & External Ventricular Drains Multimodal Monitoring: PbtO2, Microdialysis & Transcranial Doppler
16 Angiography, Electrodiagnosis & CSF Analysis
Conventional Angiography & Cranial–Spinal Shunts EMG, Nerve Conduction & Acute Muscle Disease CSF Analysis: Infection, Inflammation & Hemorrhage
17 Chapter 11: Bedside Procedures, Ultrasound & Death by Neurologic Criteria
Critical Care Procedural Skills Critical Care Ultrasound & Echocardiography Determination of Death by Neurologic Criteria
18 Chapter 12: Acute Ischemic Stroke & Reperfusion Therapies
Acute Ischemic Stroke Management & Thrombolysis Endovascular Thrombectomy & Large Vessel Occlusion Malignant Hemispheric & Cerebellar Infarction
19 Chapter 13: Spontaneous Intracerebral Hemorrhage & Intraventricular Hemorrhage
Acute Intraparenchymal Hemorrhage Management Intraventricular Hemorrhage & Hydrocephalus Surgical Evacuation & Minimally Invasive Surgery in ICH
20 Chapter 14: Aneurysmal Subarachnoid Hemorrhage & Delayed Cerebral Ischemia
Aneurysmal Subarachnoid Hemorrhage: Acute Resuscitation & Securing Delayed Cerebral Ischemia & Cerebral Vasospasm Non-Aneurysmal Subarachnoid Hemorrhage & Vascular Malformations
21 Venous, Spinal & Traumatic Vascular Disease
Cerebral Venous Thrombosis & Spinal Cord Infarction Traumatic Dissection, Carotid–Cavernous Fistula & Penetrating Injury
22 Chapter 15: Traumatic Brain & Spinal Cord Injury
Severe Traumatic Brain Injury & Contusions Acute Traumatic Spinal Cord Injury & Neurogenic Shock Spine Trauma, Fractures & Cord Syndromes
23 Chapter 16: Status Epilepticus, Seizures & Neuromuscular Emergencies
Status Epilepticus: Convulsive & Non-Convulsive Refractory & Super-Refractory Status Epilepticus Acute Neuromuscular Respiratory Failure
24 Chapter 17: Post-Cardiac Arrest Care, CNS Infections & Encephalitis
Targeted Temperature Management & Post-Cardiac Arrest Care Post-Cardiac Arrest Neuroprognostication Acute CNS Infections, Encephalitis & Inflammatory Emergencies
25 Neuroinflammation & Neurooncology
Fulminant Demyelination & Autoimmune Encephalitis Brain, Spinal & Leptomeningeal Cancer Emergencies
26 Pregnancy, Transplantation & Pediatric Care
Pregnancy, Postpartum & Post-Transplant Neurologic Care Pediatric Neurocritical Care
27 Chapter 18: Neurosurgical & Perioperative Emergencies
Postoperative Neurosurgical Complications Device Complications: EVDs, Shunts & ICP Monitors Cerebral Hyperperfusion Syndrome & Post-Interventional Emergencies
28 Chapter 19: Ethics, Palliative Care & Organ Donation in the Neuro-ICU
Communication, Surrogate Decision-Making & Conflict Resolution Neuroprognostication Ethics, Withdrawal of Life Support & Palliative Care Organ Donation & Management of the Deceased Donor
CT Perfusion & Advanced Perfusion Imaging
Key Takeaways Explain This Topic AI
CT perfusion estimates flow, volume, and transit characteristics from contrast passage; image quality and processing affect results.
Automated core and hypoperfusion thresholds are study- and software-dependent estimates rather than proof of tissue death or viability.
Use consistent units in the central-volume relation: CBF in mL/100 g/min equals 60×CBV/MTT when MTT is in seconds.
DEFUSE-3 used selected 6–16-hour patients with core below 70 mL, mismatch ratio at least 1.8, and mismatch volume at least 15 mL.
Transit delay, motion, poor bolus, seizures, and early reversible core estimates can mislead interpretation; integrate clinical and vascular findings.
Last updated: October 2026
CT Perfusion & Advanced Perfusion Imaging
CT Perfusion (CTP) provides physiological hemodynamic mapping of cerebral capillary microcirculation, extending acute ischemic stroke management far beyond conventional time-based windows. By differentiating salvageable ischemic penumbra from an operationally estimated core, CTP enables individualized reperfusion decision-making up to 24 hours from symptom onset or last known well.
Principles of Tracer Kinetics & Mathematical Deconvolution
CT perfusion is governed by indicator dilution theory and the Central Volume Principle , which states: CBF = CBV MTT \text{CBF} = \frac{\text{CBV}}{\text{MTT}} CBF = MTT CBV
Bolus Tracking & Tissue Concentration Curves
During a CTP study, 40 – 50 mL 40\text{--}50\text{ mL} 40 – 50 mL of non-ionic iodinated contrast is injected at a high flow rate ( 4 – 6 mL/s 4\text{--}6\text{ mL/s} 4 – 6 mL/s ). Cine-CT images repeatedly scan brain parenchyma over 45 – 60 seconds 45\text{--}60\text{ seconds} 45 – 60 seconds , capturing contrast entry, transit, and clearance. The change in CT attenuation over time generates a tissue concentration-time curve C tissue ( t ) C_{\text{tissue}}(t) C tissue ( t ) for each volumetric voxel.
Deconvolution & Arterial Input Function
In clinical practice, contrast injection is an extended bolus rather than an idealized instantaneous impulse. Tissue contrast concentration reflects a mathematical convolution of the contrast entering via the feeding artery—the Arterial Input Function (AIF) —and the tissue's innate vascular transit response, represented by the tissue residue function R ( t ) R(t) R ( t ) : C tissue ( t ) = CBF ⋅ [ C artery ( t ) ∗ R ( t ) ] C_{\text{tissue}}(t) = \text{CBF} \cdot [C_{\text{artery}}(t) \ast R(t)] C tissue ( t ) = CBF ⋅ [ C artery ( t ) ∗ R ( t )]
To isolate true capillary hemodynamics, computer algorithms perform mathematical deconvolution (typically block-circulant singular value decomposition [bSVD]):
AIF Selection: A major feeding artery (frequently the contralateral A1 anterior cerebral artery or M1 middle cerebral artery) is sampled to define C artery ( t ) C_{\text{artery}}(t) C artery ( t ) .
Venous Output Function (VOF): A large draining venous sinus (typically the superior sagittal sinus or torcular Herophili) is sampled to correct for partial volume averaging.
Deconvolution: Solves for the residue function R ( t ) R(t) R ( t ) and derives absolute CBF, reducing some bolus and transit effects, while technical and systemic factors can still bias the maps.
Key Perfusion Parameters & Hemodynamic Profiles
Parameter Units Physiologic Definition Normal Value (Gray Matter) Behavior in Ischemic Penumbra Behavior in Infarcted Core
Cerebral Blood Flow (CBF) mL / 100 g / min \text{mL}/100\text{g}/\text{min} mL /100 g / min Rate of arterial blood delivery through capillary beds 60 – 80 60\text{--}80 60 – 80 Moderately reduced ( > 30 % >30\% > 30% of normal) Severely collapsed ( r C B F < 30 % rCBF < 30\% r CBF < 30% )
Cerebral Blood Volume (CBV) mL / 100 g \text{mL}/100\text{g} mL /100 g Total volume of blood within microvasculature in tissue 3.5 – 5.0 3.5\text{--}5.0 3.5 – 5.0 Preserved or elevated (compensatory vasodilation) Markedly decreased (microvascular collapse)
Mean Transit Time (MTT) Seconds Average time for blood to traverse capillary bed from arteriole to venule 3.0 – 4.5 3.0\text{--}4.5 3.0 – 4.5 Prolonged ( > 6 – 8 s >6\text{--}8\text{ s} > 6 – 8 s ) Markedly prolonged
Time to Peak (TTP) Seconds Raw time from injection to maximum concentration Variable Prolonged (delay + transit) Prolonged
Time to Maximum ( T max T_{\max} T m a x ) Seconds Time to maximum of deconvolved residue function R ( t ) R(t) R ( t ) 0 to 2.0 0\text{ to }2.0 0 to 2.0 Prolonged ( T max > 6.0 s T_{\max} > 6.0\text{ s} T m a x > 6.0 s ) Prolonged ( T max > 6.0 s T_{\max} > 6.0\text{ s} T m a x > 6.0 s )
Perfusion maps estimate hemodynamic compartments; they do not directly establish irreversible histologic injury. Autoregulation, collateral delay, acquisition quality, software, and time influence the pattern. Preserved CBV may accompany threatened tissue, but low CBV or rCBF is not an infallible biological boundary.
Note
T max T_{\max} T m a x represents the time delay between the arterial input peak and the residue function peak. Unlike raw T T P TTP TTP , T max T_{\max} T m a x is mathematically corrected for proximal arterial transit delays, making T max > 6.0 seconds T_{\max} > 6.0\text{ seconds} T m a x > 6.0 seconds the trial- and software-specific operational threshold for critically hypoperfused tissue (penumbra + core).
Operational Definitions: Ischemic Core, Penumbra & Target Mismatch
Automated post-processing neuroimaging software (e.g., RAPID, Viz.ai) segments CTP maps into standardized volumetric compartments:
Ischemic Core Volume: Defined as tissue exhibiting relative Cerebral Blood Flow ( r C B F rCBF r CBF ) < 30 % < 30\% < 30% compared to the mirrored contralateral hemisphere.
Critically Hypoperfused Volume: Defined as tissue exhibiting T max > 6.0 seconds T_{\max} > 6.0\text{ seconds} T m a x > 6.0 seconds .
Ischemic Penumbra Volume (Mismatch Volume): Mismatch Volume = Volume ( T max > 6.0 s ) − Volume ( r C B F < 30 % ) \text{Mismatch Volume} = \text{Volume}(T_{\max} > 6.0\text{ s}) - \text{Volume}(rCBF < 30\%) Mismatch Volume = Volume ( T m a x > 6.0 s ) − Volume ( r CBF < 30% )
Mismatch Ratio: Mismatch Ratio = Volume ( T max > 6.0 s ) Volume ( r C B F < 30 % ) \text{Mismatch Ratio} = \frac{\text{Volume}(T_{\max} > 6.0\text{ s})}{\text{Volume}(rCBF < 30\%)} Mismatch Ratio = Volume ( r CBF < 30% ) Volume ( T m a x > 6.0 s )
Landmark Extended-Window Reperfusion Trials
The transition from rigid chronological clock times to physiological tissue viability was cemented by two landmark clinical trials extending mechanical thrombectomy from 6 up to 24 hours:
DAWN Trial ( 6 – 24 Hours 6\text{--}24\text{ Hours} 6 – 24 Hours )
The DAWN trial utilized a clinical-core mismatch paradigm, randomizing patients with anterior circulation LVO (intracranial ICA or proximal MCA) presenting between 6 and 24 hours:
Required severe clinical deficits disproportionate to small core volumes ( r C B F < 30 % rCBF < 30\% r CBF < 30% on CTP or DWI):
Age ≥ 80 years \ge 80\text{ years} ≥ 80 years : NIHSS ≥ 10 \text{NIHSS} \ge 10 NIHSS ≥ 10 and core volume < 21 mL < 21\text{ mL} < 21 mL .
Age < 80 years < 80\text{ years} < 80 years : NIHSS ≥ 10 \text{NIHSS} \ge 10 NIHSS ≥ 10 and core volume < 31 mL < 31\text{ mL} < 31 mL ; or NIHSS ≥ 20 \text{NIHSS} \ge 20 NIHSS ≥ 20 and core volume 31 to < 51 mL 31\text{ to }< 51\text{ mL} 31 to < 51 mL .
Result: EVT resulted in dramatic improvements in functional independence at 90 days ( 49 % 49\% 49% vs. 13 % 13\% 13% , number needed to treat NNT = 2.8 \text{NNT} = 2.8 NNT = 2.8 ).
DEFUSE-3 Trial ( 6 – 16 Hours 6\text{--}16\text{ Hours} 6 – 16 Hours )
The DEFUSE-3 trial evaluated anterior circulation LVO patients presenting between 6 and 16 hours using standardized automated CTP/MRI target mismatch criteria :
Initial Ischemic Core Volume: r C B F < 30 % rCBF < 30\% r CBF < 30% volume < 70 mL < 70\text{ mL} < 70 mL .
Mismatch Ratio: Volume ( T max > 6.0 s ) / Volume ( r C B F < 30 % ) ≥ 1.8 \text{Volume}(T_{\max} > 6.0\text{ s}) / \text{Volume}(rCBF < 30\%) \ge 1.8 Volume ( T m a x > 6.0 s ) / Volume ( r CBF < 30% ) ≥ 1.8 .
Absolute Mismatch Volume: Volume ( T max > 6.0 s ) − Volume ( r C B F < 30 % ) ≥ 15 mL \text{Volume}(T_{\max} > 6.0\text{ s}) - \text{Volume}(rCBF < 30\%) \ge 15\text{ mL} Volume ( T m a x > 6.0 s ) − Volume ( r CBF < 30% ) ≥ 15 mL .
Result: Endovascular thrombectomy yielded significantly higher rates of 90-day functional independence ( 45 % 45\% 45% vs. 17 % 17\% 17% ) and lower mortality ( 14 % 14\% 14% vs. 26 % 26\% 26% ).
Important
The DEFUSE-3 target mismatch parameters (core volume < 70 mL < 70\text{ mL} < 70 mL , ratio ≥ 1.8 \ge 1.8 ≥ 1.8 , absolute mismatch volume ≥ 15 mL \ge 15\text{ mL} ≥ 15 mL ) represent historic trial criteria that remain useful but do not exhaust current late-window or large-core treatment eligibility.
Diagnostic Pitfalls & Clinical Confounders
While automated CTP platforms provide rapid analysis, neurointensivists must recognize frequent clinical and technical confounders:
The "Ghost Infarct Core": In hyperacute stroke evaluations ( < 2 – 3 hours <2\text{--}3\text{ hours} < 2 – 3 hours from onset), tissue meeting the r C B F < 30 % rCBF < 30\% r CBF < 30% threshold can occasionally be reperfused and recover without evolving into permanent infarction on follow-up imaging. This phenomenon occurs because early cellular depolarization can temporarily depress microvascular flow before irreversible membrane lysis. Prematurely declaring large-core irreversibility in hyperacute presentations may inappropriately withhold life-saving thrombectomy.
Seizure and Postictal Status:
Ictal state: Focal epileptic status causes massive metabolic demand, generating focal hyperperfusion characterized by increased C B F CBF CBF , increased C B V CBV CB V , and decreased M T T MTT MTT .
Postictal paralysis (Todd's paresis): Following a focal seizure, cerebral autoregulation can cause transient regional hypoperfusion ( C B F ↓ CBF \downarrow CBF ↓ , M T T ↑ MTT \uparrow MTT ↑ ). Without an arterial occlusion on CTA, this postictal hypoperfusion mimics acute ischemia on CTP.
Severe Extracranial Internal Carotid Artery Stenosis / Tandem Lesions: High-grade cervical carotid stenosis ( > 90 % >90\% > 90% ) or chronic occlusion delays the arrival of contrast to the ipsilateral hemisphere. Blood routed through circle of Willis collateral pathways arrives seconds late. This delay uniformly prolongs T max > 6.0 seconds T_{\max} > 6.0\text{ seconds} T m a x > 6.0 seconds across the entire hemisphere, generating a massive "pseudo-penumbra" or distorting deconvolution algorithms to overestimate core volume. Always correlate CTP with cervical CTA lumen integrity.
Chronic Microvascular White Matter Disease: Areas of dense leukoaraiosis have chronically reduced capillary density, yielding low baseline C B F CBF CBF . Software algorithms may misclassify chronic microvascular ischemic white matter rarefaction as acute ischemic core.
Unit Check
Use consistent time units. With CBV in mL/100 g and MTT in seconds, multiply CBV/MTT by 60 to express CBF in mL/100 g/min. For example, CBV 4 and MTT 4 seconds yield CBF 60 mL/100 g/min.