B0 Images Research Articles

High b-value diffusion-weighted MR imaging of normal brain at 3 T

Introduction The purpose of this study was to determine the normative apparent diffusion coefficient (ADC) values at 3 T using high b-value (3000 s/mm 2) diffusion-weighted images (DWI) and compare the signal characteristics of the high b value with standard b-value (1000 s/mm 2) DWI. Methods Institutional review board approval was obtained for this prospective study which included 20 volunteers (10 M, 10 F, mean age: 38.7 ± 14.9) without any known clinical disease or radiological findings. All brain examinations were performed with 3 T MR by using similar parameters of b1000 and b3000 DWI sequences. DWI and ADC maps were obtained. Signal intensity, noise, signal to noise ratio (SNR), contrast to noise (CNR), contrast ratio (CR), and ADC values of bilateral posterior limb of internal capsule, frontal white matter, parietal gray matter, pons, thalamus, splenium of corpus callosum were measured on b1000 and b3000 DW images. Results In all anatomic locations, MR signal intensity, SNR and ADC values of b3000 images were significantly lower than MR signal intensity, SNR and ADC values of b1000 images ( p < 0.001). The CNR and CR values at the posterior limb of internal capsule and pons were significantly increased on b3000 images ( p < 0.001) and decreased in the other regions measured. Conclusion The ADC values calculated from standard b-value DWI were significantly higher than those calculated from high b-value DWI. These results agree with the previous studies. In the regions where CNR values increase with high b value, b3000 DWI images may provide additional clinical information.

A diffusion‐weighted template for gestational age‐related apparent diffusion coefficient values in the developing fetal brain

To determine the pattern of apparent diffusion coefficient (ADC) values in the normal fetal brain obtained with diffusion-weighted images (DWI) on magnetic resonance imaging (MRI) as a template for normal brain development throughout gestation. This was a prospective study of 46 fetuses without suspicion of brain pathology undergoing a total of 66 ultrasound examinations between 17 and 37 weeks of gestation. At T2-weighted MRI, four left and four right brain regions were delineated on transverse slices of the native DWI using a b-value of 0 s/mm2 (b0 images). We examined native b-value images and calculated ADC(avg), ADC(low) and ADC(high) in the basal ganglia, cerebellar hemisphere, frontal parenchyma and occipital parenchyma. Linear regression analysis was used to assess the relationship between gestational age and b0 values as well as the calculated ADC values. Delineations were successful in all fetuses for all regions except for the cerebellar hemispheres in four fetuses. There was a negative correlation between gestational age and b0 values in all examined anatomical regions (P<0.002). For ADC(avg), there were no significant changes in the basal ganglia with increasing gestational age, a positive correlation in the frontal (P<0.0001) and occipital (P=0.03) parenchyma and a negative correlation in the cerebellar hemispheres (P=0.01). For ADC(low), there was a negative correlation between gestational age and the cerebellum (P=0.0002) and basal ganglia (P=0.047), but no correlation for the frontal or occipital parenchyma. For ADC(high), there was a positive correlation with gestational age for the frontal parenchyma (P=0.004), occipital parenchyma (P=0.02) and basal ganglia (P=0.03) but there was no correlation for the cerebellum. DWI b0 values decreased in the left and right basal ganglia, cerebellar hemisphere, frontal parenchyma and occipital parenchyma between 17 and 37 weeks of gestation and ADC(avg) values increased in two out of four cerebral regions. It remains to be determined to what extent these observations differ in fetuses with suspicion of brain anomalies and whether such measurements will be useful and more predictive of outcome compared with standard MRI sequences.

Towards distortion-free fMRI using highly accelerated parallel imaging with 32 channels at 3.0 Tesla

Purpose: The inherent sensitivity of Echo Planar Imaging (EPI) to inhomogeneity in the static magnetic field, B0, generates image distortion and signal loss, especially at high B0. This is particularly problematic for functional MRI. Spin-echo based techniques offer a distortion free-alternative to EPI [1]. Combined high B0 and parallel imaging with high acceleration factors (R) promise increased SNR and reduced acquisition times. The aims of this study are (i) to compare parallel imaging using SENSE [2] and the spatio-temporal correlation (k-t) approach [3], combined with EPI and TSE, with non-accelerated acquisitions; and (ii) to investigate the use of a 32 element coil array for highly accelerated brain imaging.

Diffusion-Weighted Imaging with Sensitivity Encoding (SENSE) for Detecting Cranial Bone Marrow Metastases: Comparison with T1-Weighted Images

ObjectiveThis study was designed to determine whether diffusion-weighted imaging (DWI) with sensitivity encoding (SENSE) could detect bone marrow involvement in patients with cranial bone marrow (CBM) metastases. DWI results obtained were compared with T1-weighted imaging (T1WI) findings.Materials and MethodsDWI with sensitivity encoding (SENSE; b value = 1,000) was performed consecutively in 13 patients with CBM metastases diagnosed pathologically and radiologically. CBM lesions were dichotomized according to the involved site, i.e., skull base or calvarium. Two radiologists qualitatively evaluated the relative conspicuousness of CBM lesions and image qualities in B0 and in isotropic DWI and in T1WI. According to region of interest analysis of normal and pathologic marrow for these three sequences, absolute signal difference percentages (SD%) were calculated to quantitatively analyze lesion contrast.ResultsAll 20 lesions in 13 patients with CBM metastases revealed abnormal DWI signals in areas corresponding to T1WI abnormalities. Both skull base and calvarial lesions provided better lesion conspicuousness than T1WI and B0 images. Although the image quality of DWI was less satisfactory than that of T1WI, relatively good image qualities were obtained. Quantitatively, B0 images (SD%, 82.1 ±7.9%) showed better lesion contrast than isotropic DWI (SD%, 71.4 ±13.7%) and T1WI (SD%, 65.7 ±9.3%) images.ConclusionFor scan times of less than 30 seconds, DWI with SENSE was able to detect bone marrow involvement, and was superior to T1WI in terms of lesion conspicuity. DWI with SENSE may be helpful for the detection of cranial bone/bone marrow metastases when used in conjunction with conventional MR sequences.

Standardizing Display Conditions of Diffusion-weighted Images Using Concurrent b0 Images: A Multi-vendor Multi-institutional Study

To establish a practical method that uses concurrent b0 images to standardize the display conditions for diffusion-weighted images (DWI) that vary among institutions and interpreters. Using identical parameters, we obtained DWI for 12 healthy volunteers at 4 institutions using 4 MRI scanners from 3 vendors. Three operators manually set the window width for the images equal to the signal intensity of the normal-appearing thalamus on b0 images and set the window level at half and then exported the images to 8-bit gray-scale images. We calculated the mean pixel values of the brain objects in the images and examined the variation among scanners, operators, and subjects. Following our method, the DWI of the 12 subjects obtained using the 4 different scanners had nearly identical contrast and brightness. The mean pixel values of the brain on the exported images among the operators and subjects were not significantly different, but we found a slight, significant difference among the scanners. Determining DWI display conditions by using b0 images is a simple and practical method to standardize window width and level for evaluating diffusion abnormalities and decreasing variation among institutions and operators.

Detection of head and neck squamous cell carcinoma with diffusion weighted MRI after (chemo)radiotherapy: Correlation between radiologic and histopathologic findings

To investigate the value of diffusion weighted magnetic resonance imaging (DW-MRI) in differentiating persistent or recurrent head and neck squamous cell carcinoma (HNSCC) from nontumoral postradiotherapeutic alterations. In 26 patients with suspicion of persistent or recurrent HNSCC, MRI of the head and neck was performed, including routine turbo spin-echo (TSE) sequences and an additional echo-planar DW-MRI sequence, using a large range of b-values (0-1000 s/mm(2)). Apparent diffusion coefficient (ADC) maps were calculated. In the suspect areas at the primary site and in the suspect lymph nodes, signal intensity was measured on the native b0 and b1000 images and ADC values were calculated for these tissues. The same was done for surrounding irradiated normal tissue. Imaging results were correlated to histopathology. Signal intensity on native b0 images was significantly lower for HNSCC than for nontumoral postradiotherapeutic tissue (p < 0.0001), resulting in a sensitivity of 66.2%, specificity of 60.8%, and accuracy of 62.4%. Signal intensity on native b1000 images was significantly higher for HNSCC than for nontumoral tissue (p < 0.0001), resulting in a sensitivity of 71.6%, specificity of 71.3%, and accuracy of 71.4%. ADC values were significantly lower for HNSCC than for nontumoral tissue (p < 0.0001), resulting in a sensitivity of 94.6%, specificity of 95.9%, and accuracy of 95.5%. When compared with computed tomography, TSE-MRI and fluorodeoxyglucose-positron emission tomography, DW-MRI yielded fewer false-positive results in persistent primary site abnormalities and in persistent adenopathies, and aided in the detection of subcentimetric nodal metastases. Diffusion weighted-MRI accurately differentiates persistent or recurrent HNSCC from nontumoral tissue changes after (chemo)radiotherapy.

Evaluation of the larynx for tumour recurrence by diffusion-weighted MRI after radiotherapy: initial experience in four cases

Radiotherapy-induced changes in the soft tissues of the neck hamper the early detection of persistent or recurrent tumour by clinical examination and imaging procedures. Diffusion-weighted (DW) MRI is a non-invasive technique capable of probing tissue properties by measuring the movement of water. The purpose of the ongoing study is to examine the usefulness of DW-MRI for differentiation of persistent or recurrent tumour from post-radiotherapeutic sequelae or complications. Four patients, suspected of tumour recurrence after radiotherapy for laryngeal squamous cell carcinoma, were examined using a DW-MRI sequence on a clinical 1.5 T MR system prior to surgery. In two patients, the DW-MRI images showed an asymmetric hyperintense lesion on b1000 images with low apparent diffusion coefficient (ADC)-value, compatible with tumour on histopathology. All surrounding tissue presented high ADC values and absent signal on the b1000 images, histopathologically correlating to post-radiotherapeutic changes. The images of the third and fourth patient showed absent or minimal symmetric hyperintensity of the laryngeal soft tissues on the b1000 images and high ADC-values. In these cases, the histopathological diagnosis of radionecrosis was made and no tumour was found. In all four cases, differentiation of tumoral tissue from radiotherapy-induced tissue alterations was possible with DW-MRI.

急性期脳梗塞における拡散強調画像の信頼性：多施設実験による装置間差異の検証

Diffusion-weighted imaging (DWI) is widely applied for evaluating patients with acute ischemic stroke. However, its display conditions are different among institutions, and reliability of the apparent diffusion coefficient (ADC) has not been validated enough. Recently, we proposed an easy-to-use technique to standardize display conditions, in which window width and level are normalized by the signal intensity of brain tissue on b0 images. We carried out a multi-institutional multivendor study, and revealed that the technique successfully minimized difference in the display condition among institutions and vendors. On the other hand, we found that the ADC value is significantly different among vendors and static magnetic fields, suggesting that the ADC should be evaluated semiquantitatively. Standardization and technical advancement are considered to be necessary to improve reliability of DWI in acute stroke managements.

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, ≥.05). We concluded that b0EPI imaging could detect hemorrhagic lesions as effectively as GRE can without additional acquisition time.

Three‐point dixon technique for true water/fat decomposition with B0 inhomogeneity correction

An enhancement to Dixon's technique is described which can provide error-free decomposition of water and fat proton images even in the presence of off-resonance conditions which result from susceptibility differences, demagnetization, or shim errors. The method uses three measurements with phase shifts of 0, pi, and -pi between the fat and water resonances. The additional information provided by the third measurement is used to calculate an image of the field inhomogeneity in addition to true water and fat images. The signal-to-noise ratio (SNR) in the decomposed images is equivalent to that of a 2.7 NEX acquisition (instead of 3 NEX), yielding an SNR imaging efficiency of 95%. In addition, the B0 image which is provided may have diagnostic value in its own right. Examples of head and body scans often portray surprisingly large B0 shifts near interfaces between air or bone and soft tissue.