2 Acute Cerebral Infarction KEY FACTSPathologySecond most common worldwide cause of deathNumber one cause of US morbidityClinical IssuesMost common symptom: Focal acute neurologic deficitClinical diagnosis inaccurate in 15-20% of "strokes"Imaging FindingsBest diagnostic clue: Diffusion restriction with correlating ADC mapBest imaging tool: MR + T2*, DWICT w/o contrast if MR not availableDSA with thrombolysis in selected patients
6 Subdural HematomaAcute (± 6 hrs-3 days) hemorrhagic collection in subdural spaceNECT initial screen for aSDHMRI more sensitive for SDH & additional findings of traumatic brain injury; most appropriate in subacute phase
7 Acute Subdural Hematoma Best diagnostic clue: Crescent-shaped, homogenously hyperdense on CT, extra-axial collection that spreads diffusely over affected hemisphereMay cross sutures, not dural attachmentsMay extend along falx & tentoriumCompresses & displaces underlying brainRecurrent, mixed-age hemorrhage common → in a child raises suspicion of nonaccidental trauma!CT density & MR signal intensity vary with age & organization of hemorrhage
9 Cerebral ContusionInjury to brain surfaces involving superficial gray matterBest imaging tool: MR > CT in detecting presence, delineating extent of lesionsImaging FindingsBest diagnostic clue: Patchy superficial hemorrhages within edematous backgroundOccur in characteristic locations where brain is adjacent to bony protuberance or dural foldFocal contusions may also occur at site of depressed skull fractureFLAIR best demonstrates hyperintense cortical edemaFLAIR may show hyperintense SAHAcute: Hypointense hemorrhagic foci "bloom" on GRE (often not seen on other sequences)
10 Aneurysmal Subarachnoid Hemorrhage Best imaging tool: NECT + multislice CTABest diagnostic clue: Hyperdense CSF on NECTImaging FindingsLocation: Interhemispheric SAH suggests ACoA aneurysm, sylvian correlates with MCAPathologyMost common cause of SAH is trauma (not aneurysm rupture)aSAH causes 5% of "strokes"85% of nontraumatic SAH caused by ruptured aneurysm
12 Brain MetastasesBest imaging tool: Contrast-enhanced MRI > > CECTImaging FindingsBest diagnostic clue: Discrete parenchymal mass(es) at gray-white interfacePathologyPrevalence of metastases vs primary CNS neoplasms increasingNow account for up to 50% of all brain tumorsSeen in 25% of cancer patients at autopsyClinical IssuesMedian survival with whole brain XRT = 3-6 monthsDiagnostic ChecklistUse contrast-enhanced scans
13 Solitary Pulmonary Nodule KEY FACTSTerminologyRound or oval opacity, < 3 cm in diameterImaging Findings< 3 cm; > 90% of nodules < 2 cm are benignNodules approaching 3 cm, more likely to be malignantPrior radiographs critical for nodule detectionBenign calcification: Central nidus, laminated, popcorn, diffuseHamartomas, 1/3 show popcorn calcificationGrowth: Much overlap between benign and malignant nodulesMixed solid/part solid, up to 50% < 1.5 cm in diameter are malignantPathology90% represent (in order) granuloma, bronchogenic carcinoma, hamartoma, solitary metastasis, carcinoidImaging RecommendationsBest imaging toolCT with sequential thin cuts for presence of calcification or fatPET for nodules with high likelihood for malignancyMIP increases conspicuity for nodules
17 Hepatic Neoplasm (primary and metastatic) Imaging RecommendationsMultiphase CT (NE, arterial, venous, delayed phases) or CEMR.
18 Adrenal Adenoma Imaging Findings Best diagnostic clue: Well-circumscribed, low density, small adrenal mass on CTHomogeneous soft tissue mass of 0-20 HUWashout of adenoma: 10 min. post injection > 50%T1WI out of phase: ↑ Signal "drop-out" (lipid-rich)Washout value of > 50%: Sensitivity (96%), specificity (near 100%) for adrenal adenomaWashout value of < 50%: Indicative of either metastases or an atypical adenomaClinical IssuesAsymptomatic incidental CT imaging findingConn syndrome: Hypertension & weaknessCushing syndrome: Moon facies, truncal obesity, purple striae & buffalo humpDiagnosis: Clinical, biochemical, imaging, histology
19 Adrenal AdenomaCT is study of choice to confirm the diagnosis of adrenal adenomaCT technique: Thin cutsIf suspect adrenal adenoma, NECT alone sufficientIf CECT done, assess the followingIf lesion < 37 HU on CECT, call it adenomaIf lesion > 37 HU, on CECT, get 10 min delayed scan to determine washoutMR with in and out of phase imagingDiagnostic for lipid-rich adenomas
20 Renal Cell Carcinoma Best imaging tool Protocol advice Multiphase CT Diagnosis and stagingMR: Staging is equal or better than CT (can do subtraction images)Protocol adviceMultiphase CTMandatory: Nonenhanced and parenchymal phase (≥ 80 sec delay); optional corticomedullary (60 sec), excretory (2-5 min delay)
22 Increased Radiation Exposure from Medical Procedures More than 62 million CT scans are now performed annually in the U.S. By comparison, roughly 3 million scans were performed in 1980.New England Journal of Medicine for November 29, Drs. David J. Brenner and Eric J. Hall
23 This increase in CT usage is largely responsible for the near doubling of the average personal radiation exposure that occurred during the same period.One estimate is that in the future up to 2% of all malignancies in the U.S. could be due to radiation from CT scans. New England Journal of Medicine , November 29, 2007,
24 Reduce the CT-related radiation dose at the patient level. Replace CT evaluation with assessment by nonradiation imaging modalities, such as MRI and ultrasound, when feasible.Reduce the total number of CT scans performed.
25 An effective radiation of dose of 10 mSv can cause an increase in the lifetime cancer risk in one in 2,000 patients.
26 Radiation Dose CT Abd. - 10 mSv (3 yrs of background radiation) CT Chest - 8 mSvChest x-ray mSv (10 days of background radiation)
27 What can we do? ALARAacronym for an important principle in radiation protection and stands for "As Low As Reasonably Achievable".ACR appropriateness criteriaor go to acr.org and search site for “appropriateness criteria”
28 Some examples Perform multiphase CT’s only when needed. CT with and without contrast is not needed most of the time.i.e. Chest CT for lung nodule, most abdominal CT’s, most head CT’s.