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CT or MRI? Deciding What Test to do.

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Presentation on theme: "CT or MRI? Deciding What Test to do."— Presentation transcript:

1 CT or MRI? Deciding What Test to do.

2 Acute Cerebral Infarction
KEY FACTS Pathology Second most common worldwide cause of death Number one cause of US morbidity Clinical Issues Most common symptom: Focal acute neurologic deficit Clinical diagnosis inaccurate in 15-20% of "strokes" Imaging Findings Best diagnostic clue: Diffusion restriction with correlating ADC map Best imaging tool: MR + T2*, DWI CT w/o contrast if MR not available DSA with thrombolysis in selected patients

3 --57-year-old woman with right cerebral infarct
Stuckey, S. L. et al. Am. J. Roentgenol. 2007;189: Copyright © 2008 by the American Roentgen Ray Society

4 Hypertensive Intracranial Hemorrhage
If older patient with HTN and high suspicion for hICH, NECT If hyperacute ischemic "stroke" suspected, MR with T2* and DWI If MR shows classic hematoma + co-existing multifocal "black dots," stop If MR shows atypical hematoma, CTA If CTA inconclusive, consider DSA Protocol advice Initial screen = NECT in patients with HTN Otherwise MRI (include T2* sequences, DWI, + MRA; T1 C+ optional)


6 Subdural Hematoma Acute (± 6 hrs-3 days) hemorrhagic collection in subdural space NECT initial screen for aSDH MRI 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 hemisphere May cross sutures, not dural attachments May extend along falx & tentorium Compresses & displaces underlying brain Recurrent, mixed-age hemorrhage common → in a child raises suspicion of nonaccidental trauma! CT density & MR signal intensity vary with age & organization of hemorrhage

8 Figure 2d. Complication associated with subdural hematoma
Kiyosue, H. et al. Radiographics 2004;24: Copyright ©Radiological Society of North America, 2004

9 Cerebral Contusion Injury to brain surfaces involving superficial gray matter Best imaging tool: MR > CT in detecting presence, delineating extent of lesions Imaging Findings Best diagnostic clue: Patchy superficial hemorrhages within edematous background Occur in characteristic locations where brain is adjacent to bony protuberance or dural fold Focal contusions may also occur at site of depressed skull fracture FLAIR best demonstrates hyperintense cortical edema FLAIR may show hyperintense SAH Acute: Hypointense hemorrhagic foci "bloom" on GRE (often not seen on other sequences)

10 Aneurysmal Subarachnoid Hemorrhage
Best imaging tool: NECT + multislice CTA Best diagnostic clue: Hyperdense CSF on NECT Imaging Findings Location: Interhemispheric SAH suggests ACoA aneurysm, sylvian correlates with MCA Pathology Most common cause of SAH is trauma (not aneurysm rupture) aSAH causes 5% of "strokes" 85% of nontraumatic SAH caused by ruptured aneurysm

11 Figure 4a: (a, c) Unenhanced CT images obtained in two patients with SAH
Waaijer, A. et al. Radiology 2007;242: Copyright ©Radiological Society of North America, 2007

12 Brain Metastases Best imaging tool: Contrast-enhanced MRI > > CECT Imaging Findings Best diagnostic clue: Discrete parenchymal mass(es) at gray-white interface Pathology Prevalence of metastases vs primary CNS neoplasms increasing Now account for up to 50% of all brain tumors Seen in 25% of cancer patients at autopsy Clinical Issues Median survival with whole brain XRT = 3-6 months Diagnostic Checklist Use contrast-enhanced scans

13 Solitary Pulmonary Nodule
KEY FACTS Terminology Round or oval opacity, < 3 cm in diameter Imaging Findings < 3 cm; > 90% of nodules < 2 cm are benign Nodules approaching 3 cm, more likely to be malignant Prior radiographs critical for nodule detection Benign calcification: Central nidus, laminated, popcorn, diffuse Hamartomas, 1/3 show popcorn calcification Growth: Much overlap between benign and malignant nodules Mixed solid/part solid, up to 50% < 1.5 cm in diameter are malignant Pathology 90% represent (in order) granuloma, bronchogenic carcinoma, hamartoma, solitary metastasis, carcinoid Imaging Recommendations Best imaging tool CT with sequential thin cuts for presence of calcification or fat PET for nodules with high likelihood for malignancy MIP increases conspicuity for nodules


15 Best imaging tool Helical NE + CECT, MR + MRCP
Biliary System Best imaging tool Helical NE + CECT, MR + MRCP

16 --48-year-old woman with liver disease
Yu, J. et al. Am. J. Roentgenol. 2006;187: Copyright © 2006 by the American Roentgen Ray Society

17 Hepatic Neoplasm (primary and metastatic)
Imaging Recommendations Multiphase CT (NE, arterial, venous, delayed phases) or CEMR.

18 Adrenal Adenoma Imaging Findings
Best diagnostic clue: Well-circumscribed, low density, small adrenal mass on CT Homogeneous soft tissue mass of 0-20 HU Washout 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 adenoma Washout value of < 50%: Indicative of either metastases or an atypical adenoma Clinical Issues Asymptomatic incidental CT imaging finding Conn syndrome: Hypertension & weakness Cushing syndrome: Moon facies, truncal obesity, purple striae & buffalo hump Diagnosis: Clinical, biochemical, imaging, histology

19 Adrenal Adenoma CT is study of choice to confirm the diagnosis of adrenal adenoma CT technique: Thin cuts If suspect adrenal adenoma, NECT alone sufficient If CECT done, assess the following If lesion < 37 HU on CECT, call it adenoma If lesion > 37 HU, on CECT, get 10 min delayed scan to determine washout MR with in and out of phase imaging Diagnostic for lipid-rich adenomas

20 Renal Cell Carcinoma Best imaging tool Protocol advice
Multiphase CT Diagnosis and staging MR: Staging is equal or better than CT (can do subtraction images) Protocol advice Multiphase CT Mandatory: Nonenhanced and parenchymal phase (≥ 80 sec delay); optional corticomedullary (60 sec), excretory (2-5 min delay)

21 Figure 1. Transverse MR images in 52-year-old woman with bilateral renal masses
Hecht, E. M. et al. Radiology 2004;232: Copyright ©Radiological Society of North America, 2004

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 [1], 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 mSv Chest x-ray mSv (10 days of background radiation)

27 What can we do? ALARA acronym for an important principle in radiation protection and stands for "As Low As Reasonably Achievable". ACR appropriateness criteria or go to 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.


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