MR Imaging of Skeletal Muscle Injury in Rabbit: Comparison bet ween Diffusion and T2-weighted MR Images

PURPOSE: The purpose of this study was to apply the diffusion-weighted MR imaging technique to the early detection of skeletal muscle injury and to evaluate the usefulness of this imaging sequence. MATERIALS AND METHODS: Thirty rabbits, divided into two groups, were included in this study. Skeletal muscle injury was experimentally induced in the right thigh muscles of each rabbit by clamping with a hemostat for one minute. Four-stage clamping was applied to the rabbits in group I, but for group II there was only one stage. Diffusion and T2-weighted MR images were obtained using a 1.5T MR unit. Serial 5-and 30-minute, and 2-, 24-, and 48- hour delayed images were obtained after injury. The initial time of signal intensity change was recorded and the signal intensities of the injured sites and corresponding normal sites were measured and compared. RESULTS: On 5-minute delayed images in group I, diffusion-weighted MR images showed signal intensity changes in injured muscle in all 15 cases, but on T2-weighted images, change was not detected in three cases. In group II, 5-minute delayed T2-weighted images failed to depict the lesion in six cases, but on diffusion-weighted images, all lesions were detected. In addition, one lesion was not detected on 30-minute delayed T2- weighted images. In group II, the sensitivity of lesion detection was significantly higher on diffusion-weighted than on T2-weighted images (p = 0.0169). CONCLUSION: Diffusion-weighted MR imaging was shown to be more sensitive than T2-weighted imaging for the detection of signal intensity changes immediately after artificial injury, especially when this was of a lesser degree. These results suggest that diffusion-weighted MR imaging may be useful for the detection of early stage skeletal muscle injury.

Usefulness of 2D PC MRA of the Circle of Willis in the Evaluation of Acute Cere b ral Infarction

PURPOSE: To evaluate the usefulness of axial 2-D PC MRA of the circle of Willis in the evaluation of acute cerebral infarction. MATERIALS AND METHODS: We evaluated 42 patients with acute cerebral infarction who had undergone T2 weighted and diffusion weighted MR imaging (T2WI, DWI) and 2-D PC MRA of the circle of Willis within 72 hours of the onset of symptoms. In conjunction with high-signal lesions on DWI, the findings of 2-D PC MRA were classified as normal, stenotic, or indicative of arterial occlusion; negative 2-D PC MRA was not considered useful. In addition, the signal intensity of T2WI and DWI was compared. RESULTS: (The findings of 2-D PC MRA showed that 15 cases (35.7%) were normal, 13(31%) were stenotic, and that in 14 (33.3 %), occlusion was present). Thus, 2-D PC MRA detected vascular abnormality in 27 cases (64.3 %). On T2WI, six cases (14.3 %) showed no signal change and 36 (85.7 %) showed high signal change. In six cases without signal change, MR images were obtained within 12 hours of ictus; in one of these patients MRA findings were normal, one had stenosis, and in four, occlusion was noted. CONCLUSION: 2-D PC MRA is a useful modality for the detection of vascular abnormality in patients with acute cerebral infarct.

Renal Excretion of Gastrografin after Oral Administration: Clinical Significance in Gastric Resection Patients

PURPOSE: To evaluate the clinical significance of renal excretion of oral Gastrografin in gastric resectionpatients. MATERIAL AND METHOD: Seven days affter gastric resection, eight normal volunteers and 30 patientsunderwent abdominal and CT scanning before and 1-1.5 his after oral administiration of Gastrografin. Theattenuation coefficients of the bladder were measured and the maximal attenuation difference between pre-andpost-gastrografin administration was calculated. RESULTS: In the control group, there was no abnormal renalexcretion of oral Gastrografin, though in 83 % of patients(25 of 30), this was demonstrated as focal increase inthe density (> or = 20 HU) of the bladder and/or collecting system, or ureteral opacification. Mean maximal densitydifference was 84.4+/-82.9HU in the patient group (n=24), with renal excretion of enteral Gastrografin and,3.5+/-4.4 HU in the control group (n=7), with statistical significance (Student's t-test, p<0.01). No patientshowed either radiological or clinical evidence of direct leakage from the suture site. Patients who underwenttotal gastrectomy showed a higher maximal density difference than those in whom gastrectomy was subtotal. CONCLUSION: Unless direct leakage is visvalized on fluoroscopy or spot films, renal excretion of oralGastrografin should not be regarded as a sign of anastomotic leakage. Situations other than leakage, e. g.increased mucosal permeability or absorption, or increased bowel transit time in postoperative duration, should beconsidered as possible causes.

Diffusion-weighted Imaging of Cerebral Ischemic Infarcts: Comparison with T2-weighted Imaging in Signal Intensity

PURPOSE: To investigate whether ischemic infarct can be staged by evaluating signal intensities on diffusionweighted (DWI) and turbo spin echo T2-weighted images(T2WI). MATERIALS AND METHODS: DWI and T2WI of 27 patientswith ischemic infarct were retrospectively evaluated. Infarcts were divided into five stages depending on time ofonset : hyperacute within 12 hours, acute between 12 hours and 3 days, subacute between 3 and 10 days, earlychronic between 10 and 30 days, and late chronic after 30 days. Signal intensities of these lesions compared withnormal brain on DWI and T2WI were visually evaluated and divided into six patterns. Pattern 1 included high signalon DWI and iso-signal on T2WI, pattern 2 showed high signal on both DWI and T2WI with higher contrast on DWI,pattern 3 showed the same high signal on both images; pattern 4 revealed high signal on both images with highercontrast on T2WI, pattern 5 showed iso-signal on DWI and high signal on T2WI, and pattern 6 revealed low signal onDWI and high signal on T2WI. These five clinical stages and six MRI patterns were correlated in each patient. RESULTS: Six cases were hyperacute, six were acute, eight were subacute, three were early chronic, and four werelate chronic. At the hyperacute stage, five cases showed pattern 1 (83%) and one case, pattern 2. At the acutestage, all six cases showed pattern 2. At the subacute subcute stage, seven cases showed pattern 2(87.5%) and onecase pattern 4. At the early chronic stage, two cases showed pattern 2(66.7%) and one case, pattern 5. At the latechronic stage, all cases showed pattern 6. CONCLUSION: DWI is useful for the detection of early ischemic infarct,and stages of ischemic infarcts can be estimated by evaluating signal intensities on DWI and T2WI.