Differentiation of recent and old cerebral infarcts by diffusion-weighted MRI

We performed MRI, including diffusion-weighted imaging, in 15 patients with recurrent strokes with acute ischaemia and at least one old lesion according to the clinical history and/or CT. Routine MRI showed similar signal intensity changes in both situations. Diffusion-weighted images, however, were positive in all acute or subacute infarcts. The high signal of acutely disturbed diffusion due to intracellular oedema could also be identified in small brain stem lesions. Spatial resolution was increased by applying separate gradients in each axis instead of creating anisotropy-independent trace images. Received: 17 September 1997 Accepted: 6 April 1998     

Diffusion-weighted MRI and selection of patients for fibrinolytic therapy of acute cerebral ischaemia

Treatment of patients with acute cerebral ischaemic events remains controversial. We investigated the reversibility of high signal intensity on diffusion-weighted (DW) MRI after acute local intra-arterial fibrinolysis (LIF) and the feasibility of DW MRI for selecting patients for acute LIF. Nine patients with acute middle cerebral artery embolic occlusion underwent single-photon emission computed tomography (SPECT) and DW MRI followed by acute LIF using tissue plasminogen activator. Recanalisation was observed in all patients, and eight improved clinically. The area of high signal intensity on pretreatment DW MRI was smaller than the low-uptake area on SPECT in all patients, and went on to infarction, as detected by MRI or CT 3 days after onset in all patients. It appears to correlate, at least clinically, with irreversible brain damage. Therefore, acute LIF should not be performed in patients with areas of high signal intensity in the cortex responsible for the symptoms. SPECT remains important, because areas normal on DW MRI with low uptake on SPECT often contribute to functional prognosis. Received: 23 March 1999/Accepted: 30 August 1999     

Imaging findings of neonatal herpes simplex virus type 2 encephalitis

Introduction The CT, MR, and diffusion-weighted initial and follow-up imaging findings in neonatal herpes simplex virus type 2 (HSV-2) encephalitis were assessed. Methods The clinical, laboratory and imaging findings in 12 patients (eight girls and four boys) with proven neonatal HSV-2 encephalitis with follow-up were retrospectively reviewed. Patterns of brain involvement and distribution of lesions were studied and the contribution of diffusion-weighted imaging to the imaging diagnosis of this disease was explored. A total of 24 CT and 22 MRI studies were performed with a mean follow-up time of 38 months. Results Neonatal HSV-2 encephalitis can be multifocal or limited to only the temporal lobes, brainstem, or cerebellum. The deep gray matter structures were involved in 57% of patients, and hemorrhage was seen in more than half of the patients. CT images were normal or showed mild abnormalities in the early stages of the disease. Conventional MR images may be normal in the early stages of the disease. Lesions were initially seen only by diffusion-weighted imaging in 20% of the patients and this modality showed a substantially more extensive disease distribution in an additional 50% of patients. In 40% of patients, watershed distribution ischemic changes were observed in addition to areas of presumed direct herpetic necrosis. Conclusion Neonatal HSV-2 encephalitis has a variable imaging appearance. Diffusion-weighted MRI is an important adjunct in the imaging evaluation of this disease. Watershed distribution ischemia in areas remote from the primary herpetic lesions may be seen.     

弥漫性轴索损伤的影像诊断比较

目的 :比较CT、常规MR和扩散加权成像 (DWI)对急性、亚急性脑弥漫性轴索损伤 (DAI)的诊断价值。方法 :5 0例患者在脑损伤后 2h～ 2 0d行CT、常规MR及MRDWI ,比较病变在CT、MR各种序列上的表现特点。结果 :5 0例中CT检查阴性者 2 4例 (占 48% ) ,阳性者 2 6例 ,发现DAI病灶 75个。 5 0例在MR各种序列显示病灶 2 40个 ,其中非出血性病灶 182个 ,有 45个病灶在DWI上能观察到而常规MRI无法显示 ,占 2 4.7% ,83个病灶在DWI上信号明显高于T2 WI的病灶 ,占 45 .6% ;出血性病灶 5 8个中 ,有 12个病灶CT显示 ,而在常规MR和DWI上显示不清。结论 :对DAI急性期及亚急性期非出血性病灶的显示 ,MR常规检查比CT敏感 ,MRDWI比常规MRT2 WI敏感 ,统计学差异均有显著性意义 (P <0 .0 1)。非出血性病灶在DWI上的信号强度明显高于常规MRT2 WI ,统计学差异有显著性意义 (P <0 .0 1)。对出血性病灶的显示 ,CT优于常规MRSE序列和MRDWI。     

MRI of influenza encephalopathy in children: value of diffusion-weighted imaging

PURPOSE: Our purpose was to describe the MR findings of influenza encephalopathy and assess the value of diffusion-weighted imaging for its diagnosis. METHOD: We examined a total of five patients diagnosed as having influenza encephalopathy or encephalitis by MRI, including diffusion-weighted imaging. We analyzed the conventional images and compared them with diffusion-weighted images. RESULTS: Abnormally hyperintense lesions of varying extent and location were noted on T2-weighted and fluid-attenuated inversion recovery images in the cortex and adjacent white matter in every case. They showed no contrast enhancement. Diffusion-weighted imaging demonstrated the lesions as areas of restricted proton diffusion more clearly than conventional imaging. CONCLUSION: Influenza encephalopathy is depicted as areas of T2 elongation having a rather nonspecific distribution. Diffusion-weighted imaging can demonstrate the lesions sensitively and serve as a valuable adjunct to conventional MRI.     

Rapid MRI assessment of renal space-occupying lesions

The aim of this study was to determine whether rapidly acquired MRI sequences, taking less than 5 min imaging time, can accurately characterise renal masses. All patients found to have a renal space-occupying lesion on CT or ultrasound were asked to participate in a prospective study using rapidly acquired MRI. The MRI technique was performed on a GE Signa (General Electric, Milwaukee, Wis.) 1.5 T magnet using breath-hold coronal and axial T1 GRASS (fast spoiled gradient-recalled acquisition into steady state, FSPGR/30/90) and axial T2 fast spin-echo sequences. The results were analysed by two radiologists unaware of the CT or ultrasound findings. The CT/US was independently viewed by a third radiologist. Lesions were characterised as simple cysts, indeterminate or solid. The MR and CT/US results were correlated and the sensitivity and specificity of MR for the characterisation of simple cysts and solid renal masses calculated. A total of 144 lesions (68 patients; 29 women 39 men, age range 32–78 years, average age 60 years) were studied: 111 simple cysts; 3 hyperdense cysts; 26 renal cell carcinomas; and 4 indeterminate lesions on CT/US. There was agreement between the CT/US and MRI in 82 % of cases. All renal cell carcinomas were correctly characterised on MRI. Of simple cysts, 79 % were correctly identified using this technique. Breath-hold MRI performed in less than 5 min can accurately characterise the majority of renal masses. It is 100 % sensitive in the characterisation of renal carcinoma, and it correctly identified approximately 80 % of simple cysts. If used at the time a renal mass is detected on MRI, it would reduce the need for further investigation of the majority of incidentally detected lesions which are simple cysts. Received: 15 December 1998; Revised: 10 May 1999; Accepted: 2 July 1999     

Osteosarcoma: preliminary results of in vivo assessment of tumor necrosis after chemotherapy with diffusion- and perfusion-weighted magnetic resonance imaging

PURPOSE: We sought to evaluate diffusion and perfusion weighted 1.5 T magnetic resonance imaging (MRI) in detecting tumor necrosis with histologic correlation after preoperative chemotherapy. MATERIALS AND METHODS: Eight patients (ages 11-19 years) with histologic proven osteosarcoma of the limbs underwent T1- and fat-suppressed T2-weighted spin echo and diffusion-weighted EPI sequences (b value = 700) after 5 cycles of standard chemotherapy. Tumor volume and apparent diffusion coefficients (ADC) were calculated. Tumor signal intensities were measured in dynamic contrast enhanced T1-weighted fast gradient echo-sequences obtained every 3 seconds after an intravenous injection of gadolinium-DTPA. Perfusion parameters of first-pass tracing of contrast medium (time-to-peak, slope of contrast enhancement curve) were calculated, and perfusion maps were established. After MRI, all patients underwent limb resection, and the specimens were investigated macroscopically and histologically. The degree of tumor necrosis was assessed using the histologic Salzer-Kuntschik classification (grades 1-6) after chemotherapy. RESULTS: Necrotic areas, which were confirmed by macroscopic/histologic examination, showed ADC values up to 2.7 (mean, 2.3 +/- 0.2). Viable tumor areas revealed lower apparent diffusion coefficients (mean, 0.8 +/- 0.3). The differences in ADC between viable and necrotic tumor were highly significant (paired t test; P = 0.01). Slopes of necrotic areas ranged from 0.1 up to 5.2%/min (mean, 1.5%/min) and those of viable tumor areas from 2.8 to 31.5%/min (mean, 16.1%/min). The time-to-peak-values (TTPs) ranged from 40 to 210 seconds (mean, 131 seconds, SD 60 seconds) in necrotic tumors and from 30 to 96 seconds (mean, 55 seconds, SD 21) in viable areas of sarcomas. The differences in slope and TTP between viable and necrotic tumor were highly significant. In necrotic areas, the linear correlation between slope (%/min) and ADC (mm/s) and between TTP (s) and ADC were weak, respectively. CONCLUSION: Both dynamic contrast-enhanced MRI and diffusion-weighted MRI permit recognition of tumor necrosis induced by chemotherapy in osteosarcomas. We hypothesized that diffusion-weighted imaging is correlated directly with tumor necrosis. Perfusion-weighted imaging is correlated with microvessel density, vascular permeability, local blood volume, and flow. Therefore, perfusion weighed MRI depicts areas of tumor cell necrosis indirectly.     

Diagnosis of prostatic neuroendocrine carcinoma: Two cases report and literature review

Two cases of prostatic neuroendocrine carcinoma (PNEC) imaged by computed tomography (CT) and magnetic resonance imaging (MRI), and literature review are presented. Early enhanced CT, MRI, especially diffusion-weighted image were emphasized, the complementary roles of ultrasound, CT, MRI, clinical and laboratory characteristic’s features in achieving accurate diagnosis were valued in the preoperative diagnosis of PNEC.     

CT, MRI, and PET findings of gastric schwannoma

Gastric schwannoma is a rare tumor that accounts for only 0.2?% of all gastric tumors. We report a case of gastric schwannoma that underwent computed tomography (CT), magnetic resonance imaging (MRI), and [(18)F]-fluorodeoxyglucose positron emission tomography (FDG-PET), and its histological confirmation was acquired. Gastric schwannoma showed high intensity on T2-weighted and diffusion-weighted MRI and high maximum standardized uptake on [(18)F]-FDG-PET. Lymphadenopathy close to the tumor was also found. Although diffusion-weighted MRI, [(18)F]-FDG-PET, and the presence of lymphadenopathy could suggest malignant tumors, the detail interpretation of the other CT and MRI findings may give a clue for the diagnosis of gastric schwannoma.     

MRI findings in osmotic myelinolysis

OBJECTIVES: Osmotic myelinolysis is a distinctive clinical syndrome with characteristic CT and MR features. This study was undertaken to determine the MR appearance of these lesions on T1 and T2-weighted, and diffusion-weighted imaging (DWI) sequences with apparent diffusion coefficient (ADC) mapping. MATERIALS AND METHODS: We describe six patients who presented with deranged serum sodium levels and subsequently developed osmotic myelinolysis. CT and MRI scans were retrospectively reviewed, including the advanced functional MR sequence of DWI with ADC mapping. RESULTS: Both cerebral white matter and pontine lesions were typically hypo and hyper-intense on T1 and T2W sequences respectively. Lesions were mildly hyperintense on isotropic DWI images with elevation of the ADC. CONCLUSION: MRI is superior to CT in depicting lesions in osmotic myelinolysis. DWI with ADC mapping suggests that osmotic myelinolysis is not simply a demyelinating disorder but has similarities to multiple sclerosis.     

Comparison of perfusion computed tomography with diffusion-weighted magnetic resonance imaging in hyperacute ischemic stroke

OBJECTIVE: In this study, perfusion CT and diffusion-weighted magnetic resonance imaging (DWI) were compared as means of assessing the ischemic brain in hyperacute stroke. METHODS: Twenty patients with ischemic stroke underwent perfusion computed tomography (CT) and magnetic resonance imaging (MRI) studies <3 hours after stroke onset. Cerebral blood flow thresholds were used to delineate the ischemic lesion, penumbra, and infarct. Correlations between the volume of the hypoperfused areas, the abnormality volume in admission DWI and follow-up CT/MRI studies, and the clinical National Institutes of Health Stroke Scale (NIHSS) scores were performed. RESULTS: The volume of the ischemic (core and penumbra) lesion on admission perfusion CT was correlated with the volume of admission DWI abnormalities (r=0.89, P=0.001). The infarcted core tissue volume (on admission CT) correlated more strongly (r=0.77, P=0.0001) than the admission DWI abnormality volume (r=0.69, P=0.002) with the follow-up infarct volume on fluid-attenuated inversion recovery images. A correlation was demonstrated between infarct volume in perfusion CT and follow-up DWI abnormality volume (r=0.89, r=0.77, P=0.002). Significant correlations were found between ischemic and infarct region volumes in perfusion CT and NIHSS admission and follow-up scores (P < or = 0.01). CONCLUSIONS: Both imaging modalities provide a sufficient assessment of the hyperacute brain infarct, with significant correlation between them and the clinical condition at admission. Perfusion CT allows differentiation of the penumbra and infarct core region with significant predictive value of follow-up infarct volume and clinical outcome.     

Bilateral Vagus Nerve Neurolymphomatosis Diagnosed Using PET/CT and Diffusion-Weighted MRI

ABSTRACT: In neurolymphomatosis, malignant lymphocytes infiltrate the peripheral nervous system in the presence of a known or unknown hematological malignancy. This report describes the findings of diffusion-weighted MRI and F-FDG PET/CT in a 65-year-old man with hoarseness. Results revealed a mass with restricted diffusion on diffusion-weighted imaging in the right visceral vascular space, increased uptake of F-FDG, and other masses at distant peripheral nerves. Restaging PET/CT showed involvement of the right brachial plexus and right sciatic nerve. Biopsy and immunohistochemistry of the right vagus nerve and cervical lymphadenopathy revealed a diffuse large B-cell non-Hodgkin lymphoma.     

Value of conventional,and diffusion- and perfusion weighted MRI in the management of patients with unclear cerebral pathology,admitted to the intensive care unit

The aim of our retrospective study was to determine the extent to which diffusion- and perfusion- weighted MRI combined with conventional MRI could be helpful in the evaluation of intensive care unit (ICU) patients who have unknown or unclear cerebral pathology underlying a serious clinical condition. Twenty-one ICU patients with disparity between the findings on brain CT scan and their clinical status were studied. All patients underwent conventional MR and diffusion-weighted imaging and 14 also had MR perfusion studies. Abnormalities were present on diffusion-weighted imaging of 17 of the 21 patients and on perfusion-weighted studies of 7 of 14 patients. The MRI results changed the preliminary/working diagnosis in six patients. In eight other patients, MRI revealed additional pathology that had not been suspected clinically, and/or characterized more closely findings that had already been detected by CT or suspected clinically. MRI showed abnormalities in four of the five patients who had normal CT. MRI findings suggested a negative clinical outcome in all nine patients who subsequently died. MRI findings also suggested positive long-term outcome in five of nine patients who improved significantly as based on Glasgow and extended Glasgow outcome scales. In the three unconscious patients who had normal diffusion- and perfusion-weighted imaging the clinical outcome was good. This study suggests that MRI in seriously ill ICU patients with unclear cerebral pathology can provide information that changes, characterizes, or supports diagnoses and/or prognoses and therefore facilitates further management.     

MRI of acute post-ischemic cerebral hemorrhage in stroke patients: diagnosis with T2*-weighted gradient-echo sequences

The use of T2^*-weighted sequences has been advocated for early differentiation between hematoma and ischemia in patients with acute stroke. Early hemorrhagic transformation of ischemic stroke is an adverse event which may occur under treatment and may impair the prognosis: our aim is to evaluate the ability of T2*-weighted gradient-echo sequence (T2^* GRE) to detect post-ischemic cerebral hemorrhage. The imaging procedure included: (1) baseline CT scan at admission. (2) MRI performed within 24 h of therapy onset including: (a) dual fast spin echo T2 sequence, (b) axial isotropic echoplanar diffusion-weighted imaging sequence, (c) conventional T2* GRE, and (d) 3D TOF turbo MRA. Post-ischemic cerebral hemorrhage was diagnosed if T2^* GRE detected a focal intraparenchymal area of signal loss. The diameter of this lesion had to be more than 5 mm in order to eliminate past microbleeds. (3) Patients who showed an early suspicion of bleeding on MRI promptly had a second CT scan, and, if this one was negative for bleeding, another CT scan was performed 1 day later. All the other patients had a control CT scan during the first week. Forty-five consecutive patients have been included. T2* GRE showed intracranial bleeding in seven. The diagnosis of post-ischemic cerebral bleeding was confirmed by CT in all patients. Control CT scans did not reveal any post-ischemic cerebral hemorrhage in patients with negative MRI. In one case, hemorrhage was seen earlier on MRI than on CT scan. In conclusion, T2^* GRE appeared to be at least as efficient as CT scan in the detection of early post-ischemic cerebral hemorrhage. Received: 30 October 2000/Accepted: 23 March 2001     

磁共振扩散加权成像对结肠癌术后肝转移灶检出的临床研究

目的:探讨磁共振扩散加权成像对结直肠癌肝转移的诊断价值。方法:27例结直肠癌患者行肝脏磁共振扩散加权成像、非增强磁共振和多层CT检查。阅片前告知阅片者患者为结直肠癌术后,但不提供临床病史和既往影像学资料。结果:多层CT、非增强磁共振和扩散加权成像对肝转移灶的敏感度分别为72%(45/63)、76%(48/63)和93%(58/63),扩散加权成像对肝转移灶具有更高的敏感度且与多层CT和非增强MRI相比,差异有显著性意义。扩散加权成像对肝转移患者敏感度最高(82%),而多层CT和非增强MRI分别为77%和66%。结论:磁共振扩散加权成像对结直肠癌肝转移灶的检出率高于多层CT和非增强MRI。     

Demonstration of cerebral perfusion abnormalities in moyamoya disease using susceptibility perfusion- and diffusion-weighted MRI

We describe the use of diffusion-weighted imaging and perfusion MRI using a contrast-medium bolus in the preoperative investigation for young man presenting with a cerebral ischaemic episode as a manifestation of moyamoya disease. Received: 9 October 1997 Accepted: 1 April 1998     

Fluid-attenuated inversion recovery intraarterial signal: an early sign of hyperacute cerebral ischemia.

BACKGROUND AND PURPOSE: Early detection of arterial occlusion and perfusion abnormality is necessary for effective therapy of hyperacute cerebral ischemia. We attempted to assess the utility of the fast fluid-attenuated inversion recovery (fast-FLAIR) sequence in detecting occluded arteries as high signal (referred to as intraarterial signal) and to establish the role of fast-FLAIR in detecting ischemic penumbra of hyperacute stroke within 24 hours after ictus. METHODS: We studied 60 patients with hyperacute cerebral ischemia caused by occlusion of intracranial major arteries. We compared intraarterial signal on FLAIR images with time of flight (TOF) on MR angiograms, flow voids on T2-weighted images, hyperintense lesions on diffusion-weighted images, and results of follow-up CT or MR scans. RESULTS: In 58 (96.7%) patients, FLAIR detected intraarterial signals as early as 35 minutes after stroke onset. In 48 (80.0%) patients, intraarterial signal on FLAIR images coincided with lack of TOF on MR angiograms. In 41 (74.5%) of 55 patients, the intraarterial signals of fast T2-weighted imaging depicted occlusion better than did deficient flow void on T2-weighted images. In 25 (41.7%) of 60 patients, the area of intraarterial signal distribution was larger than the hyperintense lesion measured on diffusion-weighted images. Areas of final infarction had sizes between those of intraarterial signal distribution on FLAIR images and lesions measured on diffusion-weighted images. In 35 (87.5%) of 40 patients, areas of intraarterial signal distribution were equal to regions of abnormal perfusion. CONCLUSION: Intraarterial signal on FLAIR images is an early sign of occlusion of major arteries. FLAIR combined with diffusion-weighted imaging can be helpful to predict an area at risk for infarction (ischemic penumbra). FLAIR plays an important role for determining whether a patient should undergo perfusion study.     

Diffusion-weighted MRI: detection of cerebral ischemia before and after carotid thromboendarterectomy

PURPOSE: Conventional postoperative evaluation of patients following carotid thromboendarterectomy (TEA) consists of a clinical neurologic examination to assess neurologic deficits, color duplex ultrasound to document the surgically reestablished patency of the carotid artery, and CT for exclusion of postoperative ischemic infarctions. Recent studies prove that diffusion-weighted MRI is more sensitive in the detection of fresh insults than conventional MRI and CT. The objective of the study was to ascertain the incidence of clinically asymptomatic peri-and postoperative ischemic infarctions visualized at MRI. METHOD: We included 52 patients in the study. Fifty-one patients (31 men, 20 women; average age 68 years) underwent cranial MR examination including a diffusion-weighted sequence at 24 h prior to carotid TEA and again 24 h following the procedure. One patient did not agree to participate. RESULTS: In 29 of 51 patients (56%), neither the pre-nor the postoperative MR scans showed any diffusion abnormalities. In 16 patients (31%), however, preoperative MRI detected fresh ischemic insults. In nine patients (17.6%), the size of the insult resulted in surgery being postponed for 4 weeks. In six patients (11.8%), postoperative MRI returned findings of fresh disturbances of diffusion suggestive of ischemia that were not visualized on preoperative scans. Discrete neurologic deficits were observed in only two (3.9%) of these patients. Deficits were transient and disappeared within 72 h. CONCLUSION: Our findings underscore MRI's capacity for visualizing perioperative ischemic events. Moreover, MRI provides evidence of clinically asymptomatic embolisms that occur perioperatively.     

Diffusion-prepared fast imaging with steady-state free precession (DP-FISP): a rapid diffusion MRI technique at 7 T

Diffusion MRI is a useful imaging technique with many clinical applications. Many diffusion MRI studies have utilized echo-planar imaging (EPI) acquisition techniques. In this study, we have developed a rapid diffusion-prepared fast imaging with steady-state free precession MRI acquisition for a preclinical 7T scanner providing diffusion-weighted images in less than 500 ms and diffusion tensor imaging assessments in ～1 min with minimal image artifacts in comparison with EPI. Phantom apparent diffusion coefficient (ADC) and fractional anisotropy (FA) assessments obtained from the diffusion-prepared fast imaging with steady-state free precession (DP-FISP) acquisition resulted in good agreement with EPI and spin echo diffusion methods. The mean apparent diffusion coefficient was 2.0 × 10(-3) mm(2) /s, 1.90 × 10(-3) mm(2) /s, and 1.97 × 10(-3) mm(2) /s for DP-FISP, diffusion-weighted spin echo, and diffusion-weighted EPI, respectively. The mean fractional anisotropy was 0.073, 0.072, and 0.070 for diffusion-prepared fast imaging with steady-state free precession, diffusion-weighted spin echo, and diffusion-weighted EPI, respectively. Initial in vivo studies show reasonable ADC values in a normal mouse brain and polycystic rat kidneys.     

Audit of a policy of magnetic resonance imaging with diffusion-weighted imaging as first-line neuroimaging for in-patients with clinically suspected acute stroke

AIM: To audit the feasibility and use of diffusion-weighted (DW) magnetic resonance imaging (MRI) as initial neuroimaging for in-patients with clinically suspected acute stroke. MATERIALS AND METHODS: In April 2000, MRI with DW and T2-weighted sequence was locally instituted as initial neuroimaging for patients with clinically suspected acute stroke. This retrospective study reviewed imaging performed for in-patients with suspected acute stroke over a 9-month period. Data were collected on image type, result and need for repeat imaging. RESULTS: During the study period, 124 patients had neuroimaging for suspected cerebrovascular accident, and 119 were MRI safe. Eighty-eight (73.9%) patients underwent DW MRI as first-line investigation. Five patients were not MRI safe and 31 had computed tomography (CT) as first-line imaging due to lack of available MRI capacity. Repeat neuroimaging was performed in 16 (12.9%) patients. Study times were comparable for both types of neuroimaging: a mean of 13 min for MRI and 11 min for CT. CONCLUSION: The audit standard was achieved in 88 (73.9%) patients. The use of DW MRI as a first-line investigation for patients with a clinical diagnosis of acute stroke is achievable in a district general hospital setting.