Conspicuity of diffuse axonal injury lesions on diffusion-weighted MR imaging

OBJECTIVE: (1) To detect diffuse axonal injury (DAI) lesions by diffusion-weighted imaging (DWI), as compared with fluid-attenuated inversion recovery (FLAIR) imaging and (2) to evaluate hemorrhagic DAI lesions by b0 images obtained from DWI, as compared with gradient-echo (GRE) imaging. METHODS: We reviewed MR images of 36 patients with a diagnosis of DAI. MR imaging was performed 20 h to 14 days (mean, 3.7 days) after traumatic brain injury. We evaluated: (1) conspicuity of lesions on DWI and FLAIR and (2) conspicuity of hemorrhage in DAI lesions on b0 images and GRE imaging. RESULTS: DWI clearly depicted high-signal DAI lesions. The sensitivity of DWI to lesional conspicuity in DAI lesions was almost equal to that of FLAIR. The sensitivity of b0 images to identification of hemorrhagic DAI lesions was inferior to that of GRE. CONCLUSION: DWI is as useful as FLAIR in detecting DAI lesions. GRE imaging is still the superior tool for the evaluation of hemorrhagic DAI.     

Detection of intracranial hemorrhage: comparison between gradient-echo images and b0 images obtained from diffusion-weighted echo-planar sequences on 3.0T MRI

In this study, we compared the effectiveness of b0 echo-planar MR images (EPI) imaging with gradient recalled echo (GRE) in detecting acute hemorrhage. Brain images in 69 patients who suffered from acute infarction were reviewed. Nine of them had suffered from acute hemorrhage. Comparing b0EPI and GRE images side-by-side, we found no significant different effectiveness in detecting hemorrhage (P = .522, > or =.05). We concluded that b0EPI imaging could detect hemorrhagic lesions as effectively as GRE can without additional acquisition time.     

Fast detection of diffuse axonal damage in severe traumatic brain injury: comparison of gradient-recalled echo and turbo proton echo-planar spectroscopic imaging MRI sequences

BACKGROUND AND PURPOSE: Diffuse axonal injury (DAI) is a common type of primary neuronal injury in patients with severe traumatic brain injury (TBI), and is frequently accompanied by tissue tear hemorrhage. T2-weighted gradient-recalled echo (GRE) sequences are more sensitive than T2-weighted spin-echo images for detection of hemorrhage. The purpose of this study is to compare turbo Proton Echo Planar Spectroscopic Imaging (t-PEPSI), an extremely fast sequence, with GRE sequence in the detection of DAI. METHODS: Twenty-one patients (mean age 26.8 years) with severe TBI occurred at least 3 months earlier, underwent a brain MR Imaging study on a 1.5-T scanner. A qualitative evaluation of the t-PEPSI sequences was performed by identifying the optimal echo time and in-plane resolution. The number and size of DAI lesions, as well as the signal intensity contrast ratio (SI CR), were computed for each set of GRE and t-PEPSI images, and divided according to their anatomic location as lobar and/or deep brain. RESULTS: There was no significant difference between GRE and t-PEPSI sequences in the detection of the total number of DAI lesions (291 vs. 230, respectively). GRE sequence delineated a higher number of DAI in the temporal lobe compared to the t-PEPSI sequence (74 vs. 37, P < .004), while no differences were found for the other regions. The SI CR was significantly lower with the t-PEPSI than the GRE sequence (P < .00001). CONCLUSION: Owing to its very short scan time and high sensitivity to the hemorrhage foci, the t-PEPSI sequence may be used as an alternative to the GRE to assess brain DAI in severe TBI patients, especially if uncooperative and medically unstable.     

Detection of intracranial hemorrhage: comparison between gradient-echo images and b(0) images obtained from diffusion-weighted echo-planar sequences

BACKGROUND AND PURPOSE: Diffusion-weighted MR imaging (DWI) is commonly used as the initial and sole imaging examination for the detection of acute cerebral infarction, yet it remains controversial whether MR can detect hyperacute (<24 h) hemorrhage. Hemorrhage is best detected with gradient-echo (GRE) T2*-weighted sequences, because of their magnetic susceptibility effects. DWI uses a spin-echo echo-planar technique (EPI) that is more sensitive than spin-echo T2-weighted imaging to susceptibility effects. Our aim was to determine whether the b(0) image from the DWI-EPI sequence is as sensitive as GRE in detecting hemorrhagic lesions on imaging studies performed to identify acute infarction or hemorrhage. METHODS: All MR studies performed for clinically suspected or radiographically confirmed acute infarction or hemorrhage from 2/1/98 to 8/15/99 were retrospectively interpreted by one neuroradiologist in a blinded fashion. The sensitivity of hemorrhage detection, conspicuity of lesions, and diagnostic certainty were compared between the b(0) EPI and GRE sequences. RESULTS: We found 101 acute infarcts, of which 13 were hemorrhagic, as evidenced by the presence of hypointensity within the infarction on the GRE sequence. This finding served as the reference standard for detection of hemorrhage. Hemorrhage was diagnosed with confidence in only seven cases (54%) on b(0) images; 22 acute hematomas were hypointense on GRE images whereas 19 were hypointense on b(0) images (86%); 17 chronic hematomas were depicted on GRE images and 12 on b(0) scans (63%). Punctate hemorrhages and linear cortical staining were detected on 37 GRE studies but on only four b(0) studies. Hemorrhage was always more conspicuous on the GRE sequences. CONCLUSION: b(0) images from a DWI sequence failed to detect minimally hemorrhagic infarctions and small chronic hemorrhages associated with microangiopathy. GRE scans were more sensitive than b(0) images in the detection of these hemorrhages and should be included in emergency brain MR studies for acute infarction, especially when thrombolytic therapy is contemplated.     

多回波采集T*2加权三维梯度回波序列在弥漫性轴索损伤出血性剪切灶检出中的应用

目的 比较多回波采集的T2*WI三维梯度回波(ESWAN)序列和常规T2*WI梯度回波序列(GRE T2*WI)对弥漫性轴索损伤(DAI)出血性剪切灶的检出效能,并结合成像参数进一步探讨ESWAN序列的原理及优势.方法 回顾性分析17例DAI患者行MR检查的影像资料,比较ESWAN序列经多回波幅度平均技术后处理后的图像与常规GRE T2*WI序列对大脑总体及分区(大脑表浅区、深部区及后颅窝区)出血灶显示数量的差异,统计学分析采用配对比较秩和检验.结果 GRE T2*WI显示的出血灶在ESWAN图像上信号更低而更明显;ESWAN序列检出出血灶的中位数(范围)分别为全脑27(1～239)个、脑表浅区13(1～89)个、脑深部区5(0～111)个及后颅窝区1(0～39)个;GRE T2*WI序列检出出血灶的中位数(范围)分别为全脑7(1～34)个、脑表浅区5(1～27)个、脑深部区2(0～25)个及后颅窝区0(0～4)个.配对比较秩和检验显示两种序列在全脑及各分区的检出数量上差异均有统计学意义(Z值分别为-3.519、-3.182、-3.185、-2.677,P值均＜0.05).结论 ESWAN序列的多回波采集优势保障了足够的磁敏感效应,较GRE T2*WI序列检出小出血灶更敏感,为DAI的诊断及病情的评估提供了更多有价值的影像信息.

Abstract：

Objective To compare the efficiency of enhanced T2* weighted angiography (ESWAN) sequence with that of a conventional T2*-weighted gradient-recalled-echo (GRE T2*WI) sequence for the detection of hemorrhagic shearing lesions in patients with diffuse axonal injury (DAI). And combined with MRI parameters, to further discuss the principles and virtues of ESWAN sequence. Methods Seventeen patients with DAI were enrolled in this study. The raw data acquired from ESWAN scan were postprocessed by using the mean square root of multi-echoes. Then, the postprocessed images were compared with the conventional GRE T2* weighted images. The global and regional (superficial, deep and posterior fossa) lesion numbers determined by both sequences were compared by using Wilcoxon signed ranks test (two-tailed). Differences were considered to be significant at P≤0.05. Results Hemorrhagic lesions were more obvious on ESWAN images than those on conventional GRE T2* weighted images. The median and range value of the detected lesion numbers on ESWAN images were 27 and (1-239) in whole brain, 13 and (1-89) in cerebral superficial region, 5 and (0-111) in cerebral deep region and 1 and (0-39) in posterior fossa region, respectively; whereas, on GRE T2* weighted images, they were 7 and (1-34) in whole brain, 5 and (1-27) in cerebral superficial region, 2 and (0-25) in cerebral deep region and 0 and (0-4) in posterior fossa region, respectively. There were significant statistical differences between the two sequences in revealing the lesions in all the four regions (Z=-3.519,-3.182,-3.185,-2.677,P＜0.05). Conclusion In ESWAN sequence, multi-echo acquisition ensured sufficient magnetic susceptibility for detecting small hemorrhagic lesions. So, ESWAN is more sensitive to small hemorrhage, which revealed more hemorrhagic lesions than conventional GRE T2*WI and presented more valuable information for the diagnosis of DAI.     

Measurement of carotid wall volume and maximum area with contrast-enhanced 3D MR imaging: initial observations

PURPOSE: To investigate whether postcontrast three-dimensional (3D) magnetic resonance (MR) imaging would yield more accurate measurement of carotid artery wall volume and maximum wall area, which are both measures of plaque burden, than precontrast 3D MR imaging. MATERIALS AND METHODS: Eleven consecutive patients scheduled to undergo carotid endarterectomy were recruited for the study. A 3D fast gradient-recalled-echo sequence was applied to acquire both precontrast and postcontrast images of the carotid artery wall. The same sequence was used to image the ex vivo excised plaque as a reference for measurement of carotid wall volume and maximum wall area. RESULTS: The mean difference in maximum wall area between the precontrast in vivo measurements and the ex vivo measurements (mean +/- SD, 18.22 mm2 +/- 15.61) was significantly larger than that between the postcontrast in vivo measurements and the ex vivo measurements (12.33 mm2 +/- 14.49) (P =.02). The difference in wall volume between the precontrast in vivo measurements and the ex vivo measurements (41.81 mm3 +/- 36.51) was larger than that between the postcontrast in vivo measurements and the ex vivo measurements (32.73 mm3 +/- 35.00) (P =.004). Postcontrast images yielded better correlation with ex vivo images than did precontrast images, in both carotid luminal area (R = 0.88 for postcontrast images, R = 0.80 for precontrast images) and outer wall boundary area (R = 0.79 for postcontrast images, R = 0.71 for precontrast images) measurements. CONCLUSION: Postcontrast 3D MR imaging may be useful in the measurement of carotid artery plaque burden.     

Supraglottic carcinoma treated with curative radiation therapy: identification of prognostic groups with MR imaging

PURPOSE: To retrospectively assess the prognostic meaning of tumor characteristics depicted on pretreatment magnetic resonance (MR) images for local outcome in supraglottic squamous cell carcinoma treated with definitive radiation therapy. MATERIALS AND METHODS: Pretreatment MR images acquired in 84 patients with supraglottic carcinoma treated with curative radiation therapy were reviewed for tumor involvement of laryngeal sites including glottis, subglottis, pre-epiglottic space, laryngeal cartilages, and hypopharynx, and for extralaryngeal extension. The volume of each tumor was estimated, and mean tumor volume was calculated for the group of tumors in each T staging category. RESULTS: Results of univariate analysis showed MR imaging-determined primary tumor volume (P =.03), involvement of pre-epiglottic space (P =.008), abnormal signal intensity in thyroid cartilage (P =.04), and extralaryngeal extension beyond thyroid and/or cricoid cartilage (P =.02) to be significant predictors of local control rate. Results of multivariate analysis with the Cox regression model confirmed statistical significance for invasion of pre-epiglottic space (P =.004) and for abnormal signal intensities in thyroid cartilage adjacent to the anterior commissure (P =.04) and in cricoid cartilage (P =.01). Five-year local control rates were calculated from the regression coefficients of three independent MR imaging prognostic factors, and three prognostic groups were identified on the basis of these control rates. The 5-year local control rate in the high-risk group was 35%, significantly lower than the rates in the intermediate- and low-risk groups (60% and 89%, respectively; P =.002). CONCLUSION: MR imaging-determined pre-epiglottic space involvement and abnormal signal intensities in the thyroid cartilage adjacent to the anterior commissure and/or the cricoid cartilage are strong predictors of local outcome in supraglottic carcinoma treated with definitive radiation therapy.     

MR imaging appearance of fetal cerebral ventricular morphology

PURPOSE: To compare T2-weighted breath-hold single-shot fast spin-echo (SE) and gadolinium-enhanced spoiled gradient-echo (GRE) MR imaging with contrast material administered orally and rectally for evaluating patients with Crohn disease. MATERIALS AND METHODS: Twenty-eight patients with Crohn disease received 2% barium sulfate and water enema. The abdomen and pelvis were imaged with transverse and coronal single-shot fast SE and gadolinium-enhanced spoiled GRE MR imaging. Two radiologists reviewed the two types of images for bowel disease. The extent, severity, and conspicuity of the disease were determined. Proof of bowel disease at MR imaging was compared with that at endoscopy, barium study, and surgery. Statistical analysis was performed with the McNemar test. RESULTS: Twenty-five of 28 patients had proven abnormal bowel segments. The per-patient sensitivity of gadolinium-enhanced spoiled GRE MR imaging for the two radiologists was 100% and 96% versus 60% and 60% (P <.05) with single-shot fast SE MR imaging. Gadolinium-enhanced spoiled GRE MR images depicted more segments (54 and 52 of 61 segments; sensitivity, 89% and 85%, respectively) of the diseased bowel than did single-shot fast SE MR images (31 and 32 of 61 segments; sensitivity, 51% and 52%, respectively; P <.001). Severity of Crohn disease was correctly depicted at gadolinium-enhanced spoiled GRE imaging in 93% of patients versus in 43% of patients at single-shot fast SE imaging. CONCLUSION: In patients with Crohn disease, gadolinium-enhanced fat-suppressed spoiled GRE MR imaging better depicted the extent and severity of intestinal disease compared with single-shot fast SE imaging.     

The value of b0 images obtained from diffusion-weighted echo planar sequences for the detection of intracranial hemorrhage compared with GRE sequence

Purpose

Our aim was to evaluate the clinical utility of b0EPI images obtained from diffusion sequence for the detection of the intracranial hemorrhagic lesions, especially acute intracerebral bleeds thereby shorten the scan time particularly in the critical acute cases of stroke.

Materials and methods

Among all consecutive MR brain studies performed in our department last year, we retrospectively selected those who followed the following criteria: (1) clinically suspected or radiographically confirmed acute infarction or hemorrhage. (2) MRI imaging including DWI and T2∗ images. Sensitivity of hemorrhage detection, conspicuity of lesions, and diagnostic certainty were compared between the b0EPI and GRE sequences.

Results

There were 77 hemorrhagic lesions with a variety of pathogeneses in various locations. 76/77 (98.7%) of these lesions were hemorrhagic (hypointense) on the GRE sequences, whereas 61 (79.2%) were characterized as hemorrhagic on b0EPI images, and 16 (20.8%) were not detected. The overall difference in hemorrhage conspicuity/diagnostic certainty between GRE and b0EPI sequences was statistically significant (P < .05).

Conclusion

b0EPI sequence, although shorter in acquisition time, was inferior to GRE imaging in the detection of acute and chronic intracerebral hemorrhage.     

Intracranial hemorrhage: gradient-echo MR imaging at 1.5 T. Comparison with spin-echo imaging and clinical applications

Fifty-seven patients with hemorrhagic intracranial lesions were examined with magnetic resonance (MR) imaging at 1.5 T with use of both spin-echo (SE) and gradient-echo-acquisition (GEA) techniques to assess the clinical applications and limitations of GEA in evaluation of intracranial hemorrhage at high field strength. All GEA images were obtained with a long echo time and short flip angle to emphasize T2*-based contrast. In 30 of 61 cases, GEA images demonstrated more hemorrhagic lesions than SE images. In 14 of 61 cases, GEA images failed to depict the lesion or obscured the specific diagnosis (as depicted by SE MR imaging). The authors believe that GEA imaging in its current form has a limited but definite adjunctive role in the evaluation of intracranial hemorrhage at high field strength.     

Dynamic contrast-enhanced T2*-weighted MR imaging of tumefactive demyelinating lesions.

PURPOSE: Dynamic contrast-enhanced T2*-weighted MR imaging has been helpful in characterizing intracranial mass lesions by providing information on vascularity. Tumefactive demyelinating lesions (TDLs) can mimic intracranial neoplasms on conventional MR images, can be difficult to diagnose, and often result in surgical biopsy for suspected tumor. The purpose of this study was to determine whether dynamic contrast-enhanced T2*-weighted MR imaging can be used to distinguish between TDLs and intracranial neoplasms that share common features on conventional MR images. METHODS: We retrospectively reviewed the conventional and dynamic contrast-enhanced T2*-weighted MR images and medical records of 10 patients with tumefactive demyelinating disease that was diagnosed by either biopsy or strong clinical suspicion supported by laboratory evaluation that included CSF analysis and evoked potential tests. Twelve TDLs in 10 patients and 11 brain tumors that appeared similar on conventional MR images were studied. Relative cerebral blood volume (rCBV) was calculated from dynamic MR data and was expressed as a ratio to contralateral normal white matter. rCBV values from 11 patients with intracranial neoplasms with very similar conventional MR imaging features were used for comparison. RESULTS: The rCBV values of TDLs ranged from 0.22 to 1.79 (n = 12), with a mean of 0.88 +/- 0.46 (SD). The rCBV values of intracranial neoplasms ranged from 1.55 to 19.20 (n = 11), with a mean of 6.47 +/- 6.52. The difference in rCBV values between the two groups was statistically significant (P =.009). The difference in rCBV values between TDLs and primary cerebral lymphomas (n = 4) was less pronounced but was statistically significant (P =.005). CONCLUSION: Dynamic contrast-enhanced T2*-weighted MR imaging is a useful diagnostic tool in differentiating TDLs from intracranial neoplasms and may therefore obviate unnecessary surgical biopsy.     

Imaging findings in diffuse axonal injury after closed head trauma

Even in patients with closed head trauma, brain parenchyma can be severely injured due to disruption of axonal fibers by shearing forces during acceleration, deceleration, and rotation of the head. In this article we review the spectrum of imaging findings in patients with diffuse axonal injuries (DAI) after closed head trauma. Knowledge of the location and imaging characteristics of DAI is important to radiologists for detection and diagnosis. Common locations of DAI include: cerebral hemispheric gray-white matter interface and subcortical white matter, body and splenium of corpus callosum, basal ganglia, dorsolateral aspect of brainstem, and cerebellum. In the acute phase, CT may show punctate hemorrhages. The true extent of brain involvement is better appreciated with MR imaging, because both hemorrhagic and non-hemorrhagic lesions (gliotic scars) can be detected. The MR appearance of DAI lesions depends on several factors, including age of injury, presence of hemorrhage or blood-breakdown products (e. g., hemosiderin), and type of sequence used. Technical aspects in MR imaging of these patients are discussed. Non-hemorrhagic lesions can be detected with fluid attenuated inversion recovery (FLAIR), proton-density-, or T2-weighted images, whereas gradient echo sequences with long TE increase the visibility of old hemorrhagic lesions. Received 17 September 1997; Revision received 2 December 1997; Accepted 15 December 1997     

Traumatic brain injury: diffusion-weighted MR imaging findings.

BACKGROUND AND PURPOSE: Diffuse axonal injury (DAI) accounts for a significant portion of primary intra-axial lesions in cases of traumatic brain injury. The goal of this study was to use diffusion-weighted MR imaging to characterize DAI in the setting of acute and subacute traumatic brain injury. METHODS: Nine patients ranging in age from 26 to 78 years were examined with conventional MR imaging (including fast spin-echo T2-weighted, fluid-attenuated inversion-recovery, and gradient-echo sequences) as well as echo-planar diffusion-weighted MR imaging 1 to 18 days after traumatic injury. Lesions were characterized as DAI on the basis of their location and their appearance on conventional MR images. Trace apparent diffusion coefficient (ADC) maps were computed off-line with the diffusion-weighted and base-line images. Areas of increased signal were identified on the diffusion-weighted images, and regions of interests were used to obtain trace ADC values. RESULTS: In the nine patients studied, isotropic diffusion-weighted images showed areas of increased signal with correspondingly decreased ADC. In one case, decreased ADC was seen 18 days after the initial event. CONCLUSION: Decreased ADC can be demonstrated in patients with DAI in the acute setting and may persist into the subacute period, beyond that described for cytotoxic edema in ischemia.     

Detection of small, functional islet cell tumors in the pancreas: selection of MR imaging sequences for optimal sensitivity

PURPOSE: To determine the sensitivity and specificity of magnetic resonance (MR) imaging for depicting pancreatic small, functional islet cell tumors and the minimum number of sequences for expedient diagnosis. MATERIALS AND METHODS: Twenty-eight patients clinically suspected to have functional islet cell tumors underwent T1- and T2-weighted spin-echo (SE) MR imaging with and without fat suppression, T2-weighted fast SE imaging, and spoiled gradient-echo (GRE) imaging before and after injection of gadopentetate dimeglumine. Sensitivity, specificity, and the best and minimum number of sequences for definitive diagnosis were determined. RESULTS: MR images depicted proved islet cell tumors in 17 of 20 patients (sensitivity, 85%). Images were true-negative in eight patients with negative follow-up examination results for more than 1 year. Specificity was 100%; positive predictive value, 100%; and negative predictive value, 73%. Among 20 patients with tumor, T1-weighted SE images with fat suppression and nonenhanced spoiled GRE images each showed lesions in 15 (75%); T2-weighted conventional SE with fat suppression, in 13 (65%); gadolinium-enhanced spoiled GRE, in 12 (60%); and T2-weighted fast SE, in seven of 10 patients (70%). CONCLUSION: MR imaging accurately depicts small islet cell tumors. T2-weighted fast SE and spoiled GRE sequences usually suffice. Gadolinium-enhanced sequences are needed only if MR imaging results are equivocal or negative.     

Head and neck lesions: characterization with diffusion-weighted echo-planar MR imaging

PURPOSE: To evaluate whether apparent diffusion coefficients (ADCs) calculated from diffusion-weighted echo-planar magnetic resonance (MR) images can be used to characterize head and neck lesions. MATERIALS AND METHODS: Diffusion-weighted echo-planar MR imaging was performed with a 1.5-T MR unit in 97 head and neck lesions in 97 patients. Images were obtained with a diffusion-weighted factor, factor b, of 0, 500, and 1,000 sec/mm(2), and an ADC map was constructed. The ADCs of lesions, cerebrospinal fluid, and spinal cord were calculated. RESULTS: Acceptable images for ADC measurement were obtained in 81 (84%) patients. The mean ADC of malignant lymphomas, (0.66 +/- 0.17[SD]) x 10(-3) mm(2)/sec (n = 13), was significantly smaller (P <.001) than that of carcinomas. The mean ADC of carcinomas, (1.13 +/- 0.43) x 10(-3) mm(2)/sec (n = 36), was significantly smaller (P =.002) than that of benign solid tumors. The mean ADC of benign solid tumors, (1.56 +/- 0.51) x 10(-3) mm(2)/sec (n = 22), was significantly smaller (P =.035) than that of benign cystic lesions, (2.05 +/- 0.62) x 10(-3) mm(2)/sec (n = 10). No significant differences were seen in the mean ADC of cerebrospinal fluid and of spinal cord among four groups of lesions. When an ADC smaller than 1.22 x 10(-3) mm(2)/sec was used for predicting malignancy, the highest accuracy of 86%, with 84% sensitivity and 91% specificity, was obtained. CONCLUSION: Measurement of ADCs may be used to characterize head and neck lesions.     

Familial form of intracranial cavernous angioma: MR imaging findings in 51 families. French Society of Neurosurgery

PURPOSE: To analyze the magnetic resonance (MR) imaging features of familial cerebral cavernous angioma in non-Hispanic families. MATERIALS AND METHODS: Between November 1996 and June 1997, 51 non-Hispanic families with familial cavernous angioma were identified. Cerebral MR images in 83 symptomatic subjects and 73 asymptomatic subjects were reviewed. Spin-echo (SE) and gradient-echo (GRE) MR imaging features of cavernous angioma were recorded and, in 91 subjects with both SE and GRE images, lesions were graded as type 1, 2, 3, or 4, according to a published classification scheme. MR imaging features were compared between symptomatic and asymptomatic subjects, and sensitivities of SE and GRE images were determined. RESULTS: Multiple lesions were more common than single lesions in both symptomatic and asymptomatic subjects, with no difference in mean number of lesions between groups. More lesions were detected on GRE images than on SE images. Type 1 and type 2 lesions were more numerous in symptomatic than in asymptomatic subjects. The numbers of types 2, 3, and 4 lesions increased with age in both groups. CONCLUSION: The familial form of cavernous angioma is characterized by multiple lesions and by a correlation between lesion number and subject age. The clinical manifestation may be more closely related to the type of lesion than to the number of lesions. GRE MR images are more sensitive than SE images for demonstration of cavernous angioma.     

Study of susceptibility-weighted imaging (SWI) using a simple MR phantom

We evaluated the visibility of hypointensity regions on susceptibility-weighted (SW) magnetic resonance imaging (MRI). A commercial simple phantom filled uniformly with a gel material was demonstrated to include small regions affected by different magnetic susceptibilities compared to their surroundings. For detection of these regions in the phantom, the three-dimensional SW imaging (SWI) technique is superior to a conventional two-dimensional gradient-recalled-echo (GRE) MRI technique. The mean contrast between the hypointensity regions and their surroundings on GRE images (T2* weighted images) of 4 mm slice thickness is approximately 88% less than that on SWI of 4 mm effective slice thickness. When the effective slice thickness of SWI is increased more than 4 mm, the contrast on SW images is decreased. While the mean contrast on SWI of 7 mm effective slice thickness is approximately 75-65% compared to that of 4 mm effective slice thickness, its contrast of 7 mm is determined to be higher than that on GRE images of 4 mm slice thickness; this suggests that the SWI technique could be applied to whole brain examination by reducing the acquisition time. The quantitative results in this article are considered to be useful for evaluating the visibility of hypointensity regions on SWI, when comparing them with GRE images and varying the effective slice thickness of SWI.     

Intracranial lesion enhancement with gadolinium: T1-weighted spin-echo versus three-dimensional Fourier transform gradient-echo MR imaging.

The conspicuity of lesion enhancement with gadopentetate dimeglumine was evaluated subjectively and quantitatively through calculation of contrast-to-noise ratios (C/Ns) on T1-weighted three-dimensional (3D) Fourier transform (FT) gradient-echo (GRE) and two-dimensional (2D) FT spin-echo (SE) images of the brain in 406 consecutive patients. One hundred one enhancing intracranial lesions were present in 61 patients, including intra-(n = 76) and extraaxial (n = 25) processes of neoplastic (n = 68), infectious or inflammatory (n = 13), ischemic (n = 11), or vascular (n = 9) origin. Enhancement was apparent in all lesions on 2DFT SE and 3DFT GRE images, with similar subjective conspicuity in 86.8% (87 of 101) of lesions. Quantitative C/N measurements for 2DFT SE (mean, 17.6) and 3DFT GRE (mean, 17.2) imaging were not significantly different (P = .72). These findings, along with the other advantages of 3DFT GRE imaging, indicate that 3DFT GRE examinations are likely to play a major role in the performance of contrast-enhanced MR imaging of the brain.     

Analysis of normal-appearing white matter in multiple sclerosis: comparison of diffusion tensor MR imaging and magnetization transfer imaging.

BACKGROUND AND PURPOSE: Our purpose was to compare diffusion tensor MR and magnetization transfer imaging in assessing normal-appearing white matter (WM) regions in multiple sclerosis (MS). METHODS: Diffusion tensor, magnetization transfer, and conventional MR imaging were performed in 12 patients with MS. Fractional anisotropy, apparent diffusion coefficients (ADCs), and magnetization transfer ratios (MTRs) were measured in plaques, normal-appearing periplaque WM (PWM) regions, and normal-appearing WM regions remote from plaques. Mean fractional anisotropy, ADCs, and MTRs were calculated and compared in WM regions. RESULTS: Fractional anisotropy was lower in normal-appearing PWM regions than in remote WM regions (P <.001) but higher than in plaques (P <.001). MTRs were lower (not significantly, P =.19) in normal-appearing PWM regions than in remote regions. MTRs were higher in normal-appearing PWM regions than in plaques (P <.001). ADCs were higher in normal-appearing PWM regions than in remote regions (P =.008) but lower than in plaques (P =.001). Correlation between fractional anisotropy and MTRs of individual lesions was poor (r = 0.18) and between fractional anisotropy and ADC, modest (r = -0.39). CONCLUSION: In MS, diffusion tensor MR imaging can depict differences between WM regions that are not apparent on conventional MR images. Anisotropy measurements may be more sensitive than those of MTRs in detecting subtle abnormalities in PWM.     

Neuroimaging in pediatric brain tumors: Gd-DTPA-enhanced, hemodynamic, and diffusion MR imaging compared with MR spectroscopic imaging

BACKGROUND AND PURPOSE: Gadolinium-enhanced MR images assist in defining tumor borders; however, the relation between tumor cell extent and contrast-enhanced regions is unclear. Our aim was to improve conventional neuroimaging of pediatric brain tumors with hemodynamic, diffusion, and spectroscopic MR imaging. METHODS: We performed conventional MR and MR spectroscopic imaging in 31 children with neuroglial brain tumors. Hemodynamic MR imaging was performed in 16 patients with a first-pass intravenous bolus of gadolinium diethylenetriaminepentaacetic acid (Gd-DTPA); apparent diffusion coefficients (ADCs) were measured in 12 patients. To account for multiple measurements in a patient, we used a nested analysis of variance. RESULTS: At MR spectroscopy, choline (Cho)-containing compounds (indicating tumor) and lipid levels (indicating necrosis) did not correlate with percent Gd-DTPA enhancement on MR images. Percent enhancement was positively correlated with relative cerebral blood volumes (rCBVs) (P =.05) and negatively correlated with ADCs (P <.001). Stepwise multiple linear regression revealed that rCBV (P =.008), ADC (P =.022), and lipid (P <.001) levels were significant independent predictors of percent enhancement. Tumor spectral patterns were detected in tumor regions and outside enhancing tumor beds in patients with clinical progression; these were confirmed at neuropathologic analysis. CONCLUSION: MR spectroscopic imaging improves the assessment of pediatric brain tumors by adding biochemical information regarding tumor involvement and by depicting residual or recurrent tumor outside the Gd-DTPA-enhanced tumor bed. rCBV and ADC mapping complemented MR spectroscopic imaging. We recommend the use of MR spectroscopic imaging in addition to conventional MR imaging in assessing pediatric brain tumors.