Heidi Best, MD Journal Club March 26, 2007 P: In patients who present with symptoms suggestive of acute CVA I: Does emergent MRI C: Compared to CT O: Provide more accurate detection of CVA Clinical scenario: 66 yo female presents with 2 hours of L-sided hemiparesis. No prior history of CVA. No signs/symptoms suggestive of SAH. Is emergent MRI a better imaging choice than CT? Search strategy: PubMed, Medline, MDConsult Author info Mohr, et al 1995 USA

Study group

Study Type

Outcomes

Key Results

Weaknesses

80 pts; 68 within 4 hours of acute stoke sx; 12 within 24 hours

Multicenter, Prospective

Perfusion deficit on CT vs conventional MRI at baseline,

Infarcts detected: CT 26/61 MRI 31/61; No stat difference b/w noncont CT and T1/T2 MRI

Old MR technique, Large variability in time to scan and in interval scan, not all pts had CT and MRI, study size Small study Poor interrater agreement for extent of EIS; variability in time to scan from sx onset

Correlation of scan vs. NIHSS; Scan vs. 24 hour sx

Saur, et al; USA 2002

46 pts < 6 hrs of acute stroke sx

Singlecenter, Prospective

EIS on CT vs DWI Interrater agreement; Estimated extent of EIS

Mullins, et al; USA 2002

691 with sx of acute stroke

Multicenter, Prospective

Final dx of “stroke”(infarct, infarct with hemorrhage; infarct with transient sx);

EIS: CT 33/45 MRI 42/45 Interrater agreement of EIS: CT k=0.57 MRI k=0.85 Extent of lesion: CT k=0.40 MRI k=0.68 542/691 with final dx of “stroke” Only 101 pts with MRI/CT < 6hrs from onset: DWI 97%/100% CT 40%/92% 2nd CT 71.4%/95% Conv MRI 58%/100%

Long delay b/w 1st CT scan and MRI; Only 101 pts with MRI < 6 hrs of onset of sx; CT/MRI not in same pt

Lansberg, et al; USA 2000

19 pts < 7 hours of onset of acute stroke sx

Singlecenter, Prospective

ID of lesion Extent of lesion Interrater reliability Correlation of initial and final infarct size

Fiebach et al, 2002, Germany

54 Pts < 6 hours of acute stroke sx, NIHSS >3

Singlecenter, prospective

Detection of infarct of CT vs DWI Experts vs. residents Interrater agreement

Kidwell, et al; USA 2004

200 pts < 6 hours of acute stroke sx

Multicenter, prospective

Detection of acute hemorrhagic stroke on GRE and CT

Chalela, et al; USA 2007

356 pts with acute stroke sx

Singlecenter, prospective

Detection of acute ischemic stroke, acute hemorrhagic stroke, chronic hemorrhagic on MRI(DWI, GRE, T2) vs CT

Lesion IDed: DWI 100% CT 42-63% Interrater detection: DWI k=0.6 CT k=0.5 Infarct size: DWI “good” correlation CT “no” correlation Sensitivity of detection/experts: CT 61% DWI 91% Interrater detection: CT k=0.51 DWI k=0.84 Sensitivity by residents: CT 46% k=.38 DWI 81% k=0.62

Small study Moderate interrater reliability

Detection of any hemorrhage: MRI 71 pts CT 29; Acute hemorrhage: MRI=CT, 25pts; Chronic hemorrhage: MRI 49 pts, CT 0 Acute hemorrhagic transf of ischemia: MRI 4 pts, CT 0 SAH: MRI 0, CT 1 217/356 final dx stroke Acute ischemic stroke: MRI 83%/96% CT 16%/98% < 3hrs of sx MRI 73%/92% CT 12%/100% Acute hem stroke: MRI 81%/100% CT 89%/100%

Study size Study stopped early as MRI detected 4 hemorrhagic transform of ischemic CVA

Small study

Wide range of sx onset to scan

Clinical bottom line: MRI is more sensitive for detecting acute ischemic changes as compared to CT. MRI is at least equal to CT in detected early hemorrhagic stroke and possibly more sensitive in detecting hemorrhagic transformation of ischemic stroke. However, the logistical and economic utility of routine MRI for ALL suspected CVAs needs to be studied further. References: Chalela, et al; Magnetic resonance imaging and computed tomography in emergency assessment of patients with suspected acute stroke: a prospective comparison. Lancet 2007; 369; 293-98. J. P. Mohr, MD; Magnetic Resonance Versus Computed Tomographic Imaging in Acute Stroke. Stroke. 1995;26:807-812. Kidwell, CS, et al; Comparison of MRI and CT for detection of acute intracerebral hemorrhage. JAMA 2004; 292(15): 1823-30. Lansberg, et al; Comparison of diffusion-weighted MRI and CT in acute stroke. Neurology 2000;54:1557-1561 Mohr, et al. Diffusion-weighted MR imaging of acute stroke: correlation with T2weighted and magnetic susceptibility-enhanced MR imaging in cats. AJNR Am J Neuroradiol. 1990; 11(3):423-9 Mullins, M; CT and Conventional and Diffusion-weighted MR Imaging in Acute Stroke: Study in 691 Patients at Presentation to the Emergency Department. Radiology 2002;224:353-360. Saur, D., et al. Sensitivity and Interrater Agreement of CT and Diffusion-Weighted MR Imaging in Hyperacute Stroke. AJNR Am. J. Neuroradiol., May 1, 2003; 24(5): 878 - 885.

Commonly used MR imaging techniques are the following: • • • • • •

T1-weighted imaging (T1-WI) in which cerebrospinal fluid (CSF) has a low signal intensity in relation to brain tissue T2-weighted imaging (T2-WI) in which CSF has a high signal intensity in relation to brain tissue Spin density–weighted imaging in which CSF has a density similar to brain tissue Gradient echo imaging, which has the highest sensitivity in detecting early hemorrhagic changes Diffusion-weighted imaging (DWI) in which the images reflect microscopic random motion of water molecules Perfusion-weighted imaging (PWI) in which hemodynamically weighted MR sequences are based on passage of MR contrast through brain tissue MRI findings in acute ischemic changes Time

MRI Finding

Etiology

2-3 min

DWI - Reduced ADC

Decreased motion of protons

2-3 min

PWI - Reduced CBF, Decreased CBF CBV, MTT

0-2 h

T2-WI - Absent flow void signal

Slow flow or occlusion

0-2 h

T1-WI - Arterial enhancement

Slow flow

2-4 h

T1-WI - Subtle sulcal Cytotoxic edema effacement

2-4 h

T1-WI - Parenchymal Incomplete enhancement infarction

8h

T2-WI - Hyperintense Vasogenic and signal cytotoxic edema

16-24 h

T1-WI - Hypointense Vasogenic and signal cytotoxic edema

5-7 d

Parenchymal enhancement

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Complete infarction