Diffusion-weighted imaging of patients with subacute cerebral ischemia: comparison with conventional and contrast-enhanced MR imaging

Abstract

Background and purpose: The importance of diffusion-weighted imaging (DWI) for delineating acute ischemic lesions has been investigated extensively; however, few studies have investigated the role of DWI in the subacute stage of stroke. Because these lesions tend to appear bright throughout the first days of ischemia, owing to restricted diffusion, we speculated that DWI could also improve the detection of subacute infarcts as compared with conventional and contrast-enhanced MR imaging.

Methods: Interleaved echo-planar DWI with phase navigation was performed on a 1.5-T MR unit in a consecutive series of 53 patients (mean age, 66 +/- 14 years) with suspected recent cerebral ischemia. The interval between onset of clinical symptoms and MR imaging ranged from 1 to 14 days (mean, 6 +/- 4 days). Contrast material was given to 28 patients in a dose of 0.1 mmol/kg.

Results: DWI clearly delineated recent ischemic damage in 39 patients (74%) as compared with 33 (62%) in whom lesions were identified or suspected on conventional T2-weighted images. DWI provided information not accessible with T2-weighted imaging in 17 patients when evidence of lesion multiplicity or detection of clinically unrelated recent lesions was included for comparison. Subacute ischemic lesions were also seen more frequently on DWI sequences than on contrast-enhanced images (20 versus 13 patients). DWI was more likely to make a diagnostic contribution in the first week of stroke and in patients with small lesions or preexisting ischemic cerebral damage than was conventional MR imaging.

Conclusion: Recent ischemic damage is better shown on DWI sequences than on conventional and contrast-enhanced MR images throughout the first days after stroke and may provide further information about the origin of clinical symptoms. Adding DWI to imaging protocols for patients with subacute cerebral ischemia is recommended.

fig 1.

Graph compares the probability of lesion detection for the subgroup of 41 patients with evidence of subacute ischemic damage on any of the MR sequences used, including contrast-enhanced T1-weighted images. The first and second columns indicate the percentage of patients with a subacute lesion on T2-weighted sequences without and with knowledge of the patients' symptoms. The third column shows the relative sensitivity of DWI without clinical information

fig 2.

80-year-old patient with left hemiparesis and ataxia. A–C, DWI (TR/TE_diff/TE = approximately 1500/115/18; 2 RR intervals) study (A) clearly shows multiple recent small ischemic lesions in the right centrum semiovale. These lesions are less visible on FLAIR image (6000/130/2, TI = 1900) (B) and T2-weighted-FSE image (2900/120/1) (C) and could not be identified as areas of subacute infarction on these sequences.

fig 3.

63-year-old patient with right hemiparesis. A–L, Three days after stroke, DWI studies (approximately 1500/115/18; 2 RR intervals) (A–C) show two more clinically unexpected ischemic lesions in the cerebellum (A, B), suggestive of embolism. These two lesions would not have been definitively labeled as subacute on FLAIR (D–F) (6000/130/2, TI = 1900) or T2-weighted (2500/90/1) (G–I) sequences, especially in the presence of negative findings on contrast-enhanced images (556/14/2) (J–L).

fig 4.

A–D, Multiple tiny cortico-subcortical lesions in the right motor region on DWI (approximately 1500/115/18; 2 RR intervals) study (A) confirm the ischemic origin of mild hemiparesis 4 days after stroke. These changes might have gone undetected on T2-weighted FSE (2900/120/1) (B), FLAIR (6000/130/2, TI = 1900) (C), or contrast-enhanced (588/14/2) (D) images

fig 5.

Graph compares the percentage of patients with subacute ischemic lesions on DWI and contrast-enhanced T1-weighted sequences in the subgroup of 28 patients in whom contrast-enhanced studies were obtained

fig 6.

63-year-old patient with preexisting ischemic lesions. A–D, Mild hemiparesis is well seen on FSE (2900/120/1) (A) and FLAIR (6000/130/2, TI = 1900) (B) sequences. DWI (approximately 1500/115/18; 2 RR intervals) sequence (C) depicts the area of recent ischemic damage 7 days after stroke. Contrast-enhanced MR image (588/14/2) (D) remains negative.