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Acute and Subacute Ischemic Stroke at High-Field-Strength (3.0-T) Diffusion-weighted MR Imaging: Intraindividual Comparative Study¹

¹ From the Department of Radiology, University of Bonn, Sigmund-Freud-Str 25, D-53105 Bonn, Germany. Received August 19, 2003; revision requested October 31; final revision received February 26, 2004; accepted April 6. Address correspondence to C.K.K. (e-mail: kuhl@uni-bonn.de).

View larger version (20K): [in a new window]   Figure 1. Mean SNRs in cerebral tissue and ischemic lesions at 3.0- versus 1.5-T DW MR imaging. Mean ROI-based SNRs in the cerebellum, pons, thalamus, striatum, deep white matter (WM), and ischemic lesions (mean for all lesions in study cohort) are given. In all cerebral tissues, the mean SNR at 3.0 T is consistently higher than that in the same tissue at 1.5 T. The mean SNR in ischemic lesions at 3.0 T also is higher than that in the lesions at 1.5 T.

View larger version (30K): [in a new window]   Figure 2. Mean lesion CNRs at 1.5- versus 3.0-T DW MR imaging. (Also see Materials and Methods.) One mean CNR is given for each of the 19 patients with ischemic lesions. In cases of multiple lesions, the mean of the individual lesion CNRs is given.

View larger version (34K): [in a new window]   Figure 3. Transverse single-shot DW spin-echo echo-planar DW MR images (4345/82, isotropic diffusion imaging at b of 1000 mm–2 · sec) obtained at 1.5 T (A and B) and 3.0 T (C-E) less than 10 minutes apart show subacute ischemic lesions in 46-year-old woman with arterial hypertension, a known patent foramen ovale, and sudden onset of hemiparesis 72 hours before the DW MR imaging examination. A, B, Consecutive images obtained at 1.5 T reveal small ischemic lesions (arrows). Lesion conspicuity scores of 5 (A) and 3 (B) were assigned. C-E, On consecutive images obtained at 3.0 T, the same lesions (arrows) as in A and B are visualized; these lesions were assigned a conspicuity score of 5. Note the higher apparent SNR and the higher lesion CNR on the 3.0-T images.

View larger version (139K): [in a new window]   Figure 4. Transverse single-shot spin-echo echo-planar 1.5-T (A-C) and 3.0-T (D-F) DW MR images (4345/82, isotropic diffusion imaging at b of 1000 mm–2 · sec) obtained less than 10 minutes apart, 8 hours after the onset of clinical symptoms, show acute ischemic lesions in 60-year-old woman clinically suspected of having had an embolic infarction secondary to atrial fibrillation and of having artherosclerosis of the brain-supplying arteries (left carotid artery stenosis). A-C, Images obtained at 1.5 T show small ischemic microembolic lesions, which were assigned a conspicuity score of 4. One lesion (arrow in B) is identified in the left middle cerebral artery territory. E, One of three consecutive images obtained at 3.0 T shows the same middle cerebral artery lesion (most bottom arrow) as in B; this lesion was assigned a conspicuity score of 5. A second lesion (most top arrow) seen in the more rostral part of the temporal cortex was assigned a conspicuity score of 4. D, F, A third lesion (arrow in D) seen in the occipitotemporal junction on the left was assigned a conspicuity score of 4, and a fourth lesion (arrow in F) seen in the parietal subcortical area was assigned a conspicuity score of 3. Note the higher apparent SNR, the higher lesion CNR, and the stronger image distortions in the frontopolar region (E and F) and in the central parts close to the skull base (D) on the 3.0-T images.