Motion-probing Gradient Research Articles

Usefulness of diffusion‐weighted imaging for differentiating between desmoid tumors and malignant soft tissue tumors

To evaluate the usefulness of diffusion-weighted imaging (DWI) for differentiating between desmoid tumors and malignant soft tissue tumors. Conventional MRI and DWI were performed for 8 desmoid tumors and 74 malignant soft tissue tumors. DWI was obtained with a single-shot echo-planar imaging sequence using a 1.5 Tesla (T) MR imager. DW images were acquired with motion-probing gradient pulses applied along three directions (x, y, and z axes) with three b-factors (0, 500, and 1000 s/mm²). Two observers blinded to clinical information measured three regions of interest within the solid tumor and selected a minimum apparent diffusion coefficient () in each lesion. The mean ADC of desmoid tumors was calculated and compared with that of malignant soft tissue tumors using the Mann-Whitney U test. The mean ADC of desmoid tumors and malignant soft tissue tumors was 1.36 ± 0.48 × 10⁻³ mm² /s and 0.88 ± 0.20 × 10⁻³ mm² /s (mean ± SD), respectively. The mean ADC of the desmoid tumors was significantly higher than that of malignant soft tissue tumors (P < 0.01). DWI is considered to be useful for differentiating between desmoid tumors and malignant soft tissue tumors. In the future, further investigation in a large series is necessary.

Hepatic ADC value correlates with cirrhotic severity of patients with biliary atresia

At least 40% of survivors of biliary atresia have progressive cirrhosis even after undergoing Kasai operation. The values of hepatic apparent diffusion coefficient and apparent-diffusion-coefficient-related indices were applied to biliary atresia patients and correlated with cirrhotic severity scores of model for end-stage liver disease or pediatric end-stage liver disease model, Child-Turcotte, and Child-Pugh systems. Thirty-three biliary atresia patents (mean=1140, 61-4314 days of age) received magnetic resonance image examinations due to complications of biliary atresia from April 2008 to August 2009. Two non-breath-hold diffusion weighted imaging sequences were performed with motion-probing gradients in three directions with two b values: 0/100 and 0/500 s/mm2; 1000 ms/61.1 ms, time to repeat/time to echo; number of excitation, 1.0; 8 mm section thickness; 40 cm×40 cm field of view; 128×256 matrix in all biliary atresia patients and 18 control subjects. We used the Spearman rank correlation test to analyze the relationship among the scores of model for end-stage liver disease or pediatric end-stage liver disease model, Child-Turcotte and Child-Pugh scores and right hepatic apparent diffusion coefficients, apparent diffusion coefficient using b factor of 500-albumin product and alanine transaminase/apparent diffusion coefficient with b factor of 500 ratio. The right hepatic apparent diffusion coefficient using b factor of 100, apparent diffusion coefficient with b factor of 500 and product of apparent diffusion coefficient with b factor of 500-albumin level were significantly negatively correlated (p≤0.0125) with model for end-stage liver disease or pediatric end-stage liver disease model, Child-Turcotte, and Child-Pugh scores of biliary atresia patients. The ratio of alanine transaminase level/right hepatic apparent diffusion coefficient with b factor of 500 was also significantly (p≤0.0251), moderately correlated with Child-Turcotte and Child-Pugh scores (rho=0.5256 and 0.7518, respectively). Right hepatic apparent diffusion coefficient with b factor of 500 and alanine transaminase/right hepatic apparent diffusion coefficient with b factor of 500 can be useful for long-term follow-up of cirrhotic severity in biliary atresia patients.

Diagnostic Value of SPIO-mediated Breath-hold, Black-blood, Fluid-attenuated, Inversion Recovery (BH-BB-FLAIR) Imaging in Patients with Hepatocellular Carcinomas

We assessed the value of adding a breath-hold, black-blood, fluid-attenuated, inversion recovery (BH-BB-FLAIR) sequence with a small motion-probing gradient (b=10 s/mm(2)) using superparamagnetic iron oxide (SPIO) to our present studies that utilize SPIO to detect hepatocellular carcinoma (HCC). We used inversion recovery (IR) in a FLAIR sequence to suppress signals from cysts and a low b-value to suppress vessel signals and provide higher signal to noise than that using high b-value diffusion-weighted imaging. Use of SPIO is expected to reduce the signal in both normal liver parenchyma and in most benign lesions. In 19 patients, we reviewed 38 HCC nodules diagnosed by CT arterioportography (CTAP) and CT during hepatic arteriography (CTHA). We divided SPIO-mediated images into sets, those obtained with and without BH-BB-FLAIR. Six radiologists individually interpreted the 2 image sets and sorted them by their confidence levels for the presence of HCC, and we calculated the area under the receiver operating characteristic (ROC) curve (Az) for each image set. On images obtained with BH-BB-FLAIR after SPIO administration, 33 of the 38 HCC nodules appeared as areas of high signal and cyst signal was extinguished. The ROC analysis showed significantly higher Az values in the set with BH-BB-FLAIR (0.89) than in the set without (0.83). Adding BH-BB-FLAIR to existing SPIO-mediated imaging protocols improved detection of HCC nodules and added only 24 s to the scan time.

Diffusion-weighted MR neurography of the sacral plexus with unidirectional motion probing gradients

BackgroundThis technical note introduces diffusion-weighted (DW) MR neurography (MRN) of the sacral plexus with unidirectional motion probing gradients (MPGs).MethodsThis is compared with DW MRN with three-directional and six-directional MPGs.Results and conclusionThis paper indicates that DW MRN of the sacral plexus should be performed with unidirectional MPGs.

Influence of cardiac motion on diffusion-weighted magnetic resonance imaging of the liver

To assess cardiac motion-induced signal loss in diffusion-weighted magnetic resonance imaging (DWI) of the liver using dynamic DWI. Three volunteers underwent dynamic coronal DWI of the liver under breathholding, in the diastolic (DWI(diast)) or systolic (DWI(syst)) cardiac phase, and with motion probing gradients (MPGs) in phase encoding (P, left-right), frequency encoding (M, superior-inferior), or slice select (S, anterior-posterior) direction. Liver-to-background contrasts (LBCs) of DWI(syst) were compared to those of DWI(diast), for both the left and right liver lobes, using nonparametric tests. Signal decrease ratios (SDRs) were calculated as (1-(LBCDWI(syst)/LBCDWI(diast))) x 100%. DWI(syst) was further analyzed to determine which direction of MPGs was most affected by cardiac motion. In the left liver lobe, LBCs of DWI(syst) (median 3.35) were significantly lower (P < 0.0001) than those of DWI(diast) (median 4.84). In the right liver lobe, LBCs of DWI(syst) (median 4.17) were also significantly lower (P < 0.0001) than those of DWI(diast) (median 5.35 ). SDRs of the left and right liver lobes were 25.5% and 17.3%, respectively. In DWI(syst), the significantly lowest (P < 0.05) LBCs were observed in the M direction (left liver lobe) and P direction (right liver lobe) of MPGs. Signal intensity of both liver lobes are affected by cardiac motion in DWI. In the left liver lobe, signal loss especially occurs in the superior-inferior direction of MPGs, whereas in the right lobe, signal loss especially occurs in the left-right direction of MPGs.

Hybrid of opposite‐contrast MR angiography (HOP‐MRA) combining time‐of‐flight and flow‐sensitive black‐blood contrasts

For the purpose of visualizing low-flow as well as high-flow blood vessels without using contrast agents, we propose a new technique called a hybrid of opposite-contrast MR angiography (HOP-MRA). HOP-MRA is a combination of standard time-of-flight (TOF) using a full first-order velocity-compensation for white-blood (WB) and flow-sensitive black-blood (FSBB) techniques, which use motion-probing gradients to introduce intravoxel flow dephasing. A dual-echo three-dimensional gradient echo sequence was used to reduce both imaging time and misregistration. HOP-MRA images were obtained using a simple-weighted subtraction (SWS) or a frequency-weighted subtraction (FWS) applying different spatial filtering for WB and BB images. We then assessed the relationships among the contrast-to-noise ratios (CNR) of the blood-to-background signals for those three images. In both volunteer and clinical brain studies, low-flow vessels were well visualized and the background signal was well suppressed by HOP-MRA compared with standard TOF- or BB-MRA. The FWS was better than the SWS when whole-maximum intensity projection was performed on a larger volume including with different types of tissue. The proposed HOP-MRA was proven to visualize low-flow to high-flow vessels and, therefore, demonstrates excellent potential to become a clinically useful technique, especially for visualizing collateral vessels which is difficult with standard TOF-MRA.

Higher Sensitivity and Specificity for Diffusion-weighted Imaging of Malignant Lung Lesions without Apparent Diffusion Coefficient Quantification

To compare the performance of apparent diffusion coefficient (ADC) with that of signal intensity of the lesion-to-spinal cord ratio (LSR) in differentiating lung cancer from benign lesions on high-b value diffusion-weighted (DW) magnetic resonance (MR) images. This study received institutional review board approval; written informed consent was provided by all patients. Twenty-eight patients (six women, 22 men; mean age, 64.2 years) with pulmonary nodules seen at chest computed tomography were prospectively reviewed. Two DW images with different motion-probing gradient strengths (b(h) = 1000 sec/mm(2) and b(l) = 0 sec/mm(2)) were analyzed semiquantitatively by measuring the signal intensities of the lesions and the spinal cord. ADC was calculated by using linear regression analysis of the natural logarithm of mean signal intensity versus the gradient factor. For reference, LSR was also measured on the same image with a diffusion gradient of b(h) = 1000 sec/mm(2). The LSR of cancer nodules was significantly higher than that of benign lesions, while there were no significant differences between them in relation to ADC. In the receiver operating characteristic curve analysis, LSR had a higher area under the curve than did ADC (0.911 vs 0.600). By using a cutoff value of 1.135, LSR had a positive predictive value of 86.7% a negative predictive value of 90%, and an accuracy of 85.7% for the detection of lung cancer with LSR. LSR measurement on high-b value DW imaging may be useful for differentiating between benign and malignant lung nodules.

Diffusion Tensor Tractography in the Head-and-Neck Region Using a Clinical 3-T MR Scanner

Diffusion tensor tractography (DTT) for neural fibers of the head-and-neck region at 3T has not been reported. The purpose of this study was to evaluate the feasibility of using DTT for visualizing neural fibers in the head-and-neck region at 3T and to explore the use of this method in patients with head-and-neck mass lesions. Using a 3T scanner, we obtained magnetic resonance images of the head and neck region in 5 healthy volunteers and 5 patients with head and neck mass lesions. All subjects underwent anatomic T1-weighted and diffusion-tensor imaging using a sequence with six motion-probing gradient orientations, a b value of 800 second/mm(2), and a 128 x 128 pixel matrix. Fiber tracking was with the continuous tracking method. Different postprocessing parameters were investigated to optimize fiber density detection and minimize noise. In five patients with head-and-neck mass lesions, comparison of tractography results and operative findings with regards to mass and nerve relationship was also performed by two observers. Using the two regions-of-interest method, the greatest fiber density of presumed inferior alveolar nerves was depicted at a maximum angle of 40 degrees and a minimum fiber length of 10 mm. DTT was successfully depicted in all 5 patients. In 4 patients, the relationship between DTT and operative findings was coincided or similar. The interobserver agreement was good. DTT of the neural fibers in the head and neck region is feasible using a clinical 3T magnetic resonance scanner. Data from a small number of patients with head-and-neck lesions show good agreement between tractography and operative results.

ＭＰＧ印加軸数が拡散テンソル解析に及ぼす影響について

When diffusion tensor was analyzed, increasing motion probing gradient (MPG) directions and increasing signal-to-noise ratio (SNR) as result might influence diffusion tensor calculation. This study determined that mean diffusivity (MD) and fractional anisotropy (FA) are calculated by changing MPG-directions or SNR in the volunteer. There were no statistically significant differences in MD, which is calculated from all scanning parameters (p>0.05). FA of the caudate nucleus was similar as well. However, there were statistically significant differences between FA calculated from 31 MPG-directions and from 13 MPG-directions or less for the frontal lobe and caudate nucleus (p<0.05). If SNR of a trace image is 30 or more, FA wasn't affected by SNR (p>0.05). To calculate FA, minimum MPG-directions that were not statistically different compared with 31 MPG-directions were 15 MPG-directions (p<0.05).

Estimation of Cell Membrane Permeability and Intracellular Diffusion Coefficient of Human Gray Matter

The signal intensity of diffusion-weighted imaging (DWI) is sensitive to the intra- and extracellular diffusion coefficient of water and cell membrane permeability. We applied a method we proposed in previous papers to estimate noninvasively the membrane permeability and intracellular diffusion coefficient of normal human brain (gray matter) in 3 normal volunteers. We theoretically compared predicted signals and experiment results using a 1.5-tesla magnetic resonance (MR) imaging system. We acquired images using an echo planar imaging (EPI) sequence, applying motion-probing gradient (MPG) pulses in 3 directions. We periodically performed numerical simulations for various combinations of membrane permeability and intracellular diffusion coefficients using the finite-difference method. By minimizing the difference between signals obtained experimentally and those from numerical simulation, we could estimate membrane permeability (76+/-9 mm2/s mum) and intracellular diffusion coefficient (1.0+/-0.0 mm2/s) for the human brain. The estimated membrane permeability was the criterion value for diagnosing disease in gray matter.

拡散強調画像における歪みの検討

The definitional equation of the distortion of echo planar imaging(EPI)was examined. We compared measured values with calculated values by using the definitional equation of the chemical shift of the EPI method that first composed the diffusion-weighted image, and examined the possibility of applying it to the distortion. The results showed that the chemical shift with the definitional equation and the measurement corresponded, and the correlation between the chemical shift and the distortion was acquired. Next, the distortion of each images that composed DWI with the increase and the sign acceptable method difference of b value. The difference in the distortion between each image has increased with the increase in b value. It was assumed that the influence of the eddy currents was due to the high motion probing gradient.

Shift of the Pyramidal Tract During Resection of the Intraaxial Brain Tumors Estimated by Intraoperative Diffusion-Weighted Imaging

The present study evaluated the shift of the pyramidal tract during resection of 17 proximal intraaxial brain tumors. In each case intraoperative diffusion-weighted (iDW) magnetic resonance imaging with a motion-probing gradient applied in the anteroposterior direction was performed using a scanner with a 0.3 T vertical magnetic field. The position of the white matter bundles containing the pyramidal tract was estimated on the coronal images before and after resection of the neoplasm, and both quantitative and directional evaluation of its displacement was done. In all cases iDW imaging provided visualization of the structure of interest. The magnitude of the pyramidal tract displacement due to removal of the neoplasm varied from 0.5 to 8.7 mm (mean 4.4 +/- 2.5 mm) on the lesion side and from 0 to 3.6 mm (mean 1.3 +/- 1.1 mm) on the normal side (p < 0.001). Tumor location in regards to the pyramidal tract was significantly associated with the direction of the pyramidal tract displacement (p < 0.05). Outward shift occurred in 10 out of 13 cases of the lateral neoplasms, whereas in all 4 superomedial tumors inward shift was marked. In conclusion, the direction of the pyramidal tract displacement during resection of the proximal intraaxial brain tumors is mainly determined by position of the neoplasm, but can be unpredictable in some cases, which necessitates use of subcortical brain mapping and intraoperative imaging, particularly iDW imaging with updated neuronavigation.

Visualization of the lenticulostriate artery with flow‐sensitive black‐blood acquisition in comparison with time‐of‐flight MR angiography

To evaluate the capability of flow-sensitive black blood (FSBB) acquisition to visualize the lenticulostriate artery (LSA) in comparison with time-of-flight (TOF) angiography. Twenty-one healthy subjects (13 males and 8 females, 19-44 years old) were enrolled in this study after obtaining written informed consent. Magnetic resonance imaging (MRI) examinations were performed with FSBB and TOF to visualize the LSA using a 1.5T MRI unit. In FSBB acquisition a motion probing gradient of b = 4 sec/mm(2) was applied to dephase blood flow. Images were reconstructed into coronal sections and were evaluated in terms of number, length, and image quality at origins and distal areas of visualized LSA branches with a four-point scale. In all, 145 LSA branches were visualized with FSBB and 66 branches with TOF. There was no LSA visualized only with TOF. In all evaluated terms, FSBB was significantly better than TOF. We could better visualize the LSA with FSBB than with TOF, both quantitatively and qualitatively. FSBB is a promising method, although it remains to be evaluated in clinical cases.

Value of Apparent Diffusion Coefficient(ADC) of Diffusion eighted Magnetic Resonance Imaging in Common Renal Disease Diagnosis

Objective To find the value of the apparent diffusion coefficient (ADC) of diffusion weighted magnetic resonance imaging of common renal diseases. Methods There were 30 healthy subjects and 81 patients with renal lesions (56 cases of renal carcinoma, 18 lesions of 12 cases of renal angiomyolipoma, and 21 lesions of 13 cases of renal cysts). Conventional magnetic resonance imaging and diffusion weighted magnetic resonance imaging were carried out. We measured the average ADC value of the renal lesions and normal kidneys. ADC maps from different b values were generated by a statistical package. Results The ADC values of normal kidneys with three different motion-probing gradients(b=500, 800, 1000 sec/mm 2) were 2.78 ± 0.14, × 10 −3mm 2s −1, 2.45 ± 0.13, × 10 −3mm 2s −1, 2.13 ± 0.14, × 10 −3mm 2s −1, respectively. The ADC values of renal cell carcinoma with three different motion-probing gradients(b=500, 800, 1000 sec/mm 2) were 1.63 ± 0.14 × 10 −3mm 2s −1, 1.31± 0.18 × 10 −3mm 2s −1, 1.07 ± 0.15, 10 −3mm 2s −1, respectively. Among the renal cell carcinoma, the ADC value of clear cell type were 1.67 ± 0.09, × 10 −3mm 2s −1, 1.36 ± 0.13, × 10 −3mm 2s −1, 1.15 ± 0.14, × 10 −3mm 2s −1, respectively; the ADC values of granular cell type were 1.59 ± 0.19, × 10 −3mm 2s −1, 1.25 ± 0.22, × 10 −3mm 2s −1, 0.97 ± 0.12, × 10 −3mm 2s −1, respectively. The ADC values of renal angiomyolipoma with three different motion-probing gradients(b=500, 800, 1000 sec/mm 2) were 0.88± 0.08, 10 −3mm 2s −1, 0.63 ± 0.07, × 10 −3mm 2s −1, 0.43 ± 0.04, × 10 −3mm 2s −1, respectively. The ADC values of renal cystic lesions with three different motion-probing gradients(b=500, 800, 1000 sec/mm 2) were 3.73 ± 0.18, × 10 −3mm 2s −1, 3.44 ± 0.13, × 10 −3mm 2s −1, 3.09 ± 0.21, × 10 −3mm 2s −1, respectively. Statistically significant differences exists between the ADC values of normal kidney, renal carcinomas, renal angiomyolipomas and renal cysts when the b value is the same. Among the different cell types of renal carcinomas, the ADC value of granular cell carcinoma is lower than that of clear cell carcinomas. Conclusion It is of benefit in diagnosing and distinguishing between benign and malignant renal tumors to know the ADC values in diffusion weighted magnetic resonance imaging. Furthermore, these values help to know the internal structure of the tumor and the tumor typel, which is helpful to the treatment and in predicting the patient's prognosis.

Abdominal apparent diffusion coefficient measurements: effect of diffusion-weighted image quality and usefulness of anisotropic images

This study aimed to assess the effect of diffusion-weighted image (DWI) quality on abdominal apparent diffusion coefficient (ADC) measurements and the usefulness of anisotropic images. Twenty-six patients (10 men and 16 women; mean, 58.1 years) who underwent DW imaging and were diagnosed not to have any abdominal diseases were analyzed. Single-shot spin-echo echo-planar DW imaging was performed, and one isotropic and three orthogonal anisotropic images were created. ADCs were calculated for liver (four segments), spleen, pancreas (head, body, tail) and renal parenchyma. Image quality for each organ part was scored visually. We estimated the correlation between ADC and image quality and evaluated the feasibility of using anisotropic images. ADCs and image quality were affected by motion probing gradient directions in the liver and pancreas. A significant inverse correlation was found between ADC and image quality. The r values for isotropic images were -.46, -.48, -.70 and -.28 for the liver, spleen, pancreas and renal parenchyma, respectively. Anisotropic images had the best quality and lowest ADC in at least one organ part in 17 patients. DWIs with the best quality among isotropic and anisotropic images should be used in the liver and pancreas.

Estimation of cell membrane permeability of the rat brain using diffusion magnetic resonance imaging

We propose a method to noninvasively evaluate the permeability of the cell membrane in the rat brain using diffusion magnetic resonance imaging (MRI). Diffusion MRI reflects the intra- and extracellular diffusion coefficients of water and cell membrane permeability. The images were acquired using a 4.7T MRI system with applications to motion-probing gradients in six directions. Numerical simulations based on the finite-difference method were carried out for estimating diffusion MRI signals with various combinations of membrane permeability and intracellular diffusion coefficient values. We defined an evaluative function as the difference between the signals estimated by simulation and experimentally obtained signals. We found that the combination of membrane permeability and intracellular diffusion coefficient in the simulation corresponding to the minimum value of the evaluative function leads to an estimation of these properties of the rat brain. The estimated intracellular diffusion coefficient and membrane permeability were (1.3±0.1)×10−3mm2∕s and 74±23μm∕s, respectively. Our method is useful for noninvasively estimating the cell membrane permeability of biological tissues, and is easily applicable to human tissues.

Depiction of the Cranial Nerves Within the Brain Stem with Use of PROPELLER Multishot Diffusion-Weighted Imaging

Despite the recent progress of MR imaging, visualization of the cranial nerves within the brain stem has not been accomplished. Periodically rotated overlapping parallel lines with enhanced reconstruction (PROPELLER) multishot diffusion-weighted imaging, an effective method for compensating for motion and distortion, offers high-quality diffusion-weighted images. We succeeded in depicting the cranial nerves within the brain stem in some subjects by using this method with motion-probing gradient applied in the superior-inferior direction.

Estimation of the Anterior Extent of the Meyer Loop Using MR Tractography

We read with interest the recent study by Yamamoto et al in the American Journal of Neuroradiology .[1][1] The authors aimed to determine the optimal directional motion-probing gradient (MPG) setting for imaging the optic radiations by means of MR tractography by evaluating images captured with

拡散ＭＲＩを用いたラットの細胞膜透過率評価

We propose a method of non-invasively evaluating the permeability of cell membranes in normal rat brain using diffusion magnetic resonance imaging (MRI). Diffusion MRI signals reflect the intra- and extracellular diffusion coefficients of water molecules in permeable biological tissues and cell membranes. The signals were acquired using a 4.7 T MRI system and applying a motion-probing gradient (MPG) in six directions. Numerical simulations using the finite-difference method were conducted for various combinations of intracellular diffusion coefficients and cell-membrane permeabilities. We defined the evaluative function as the difference between the signals from numerical simulations and experimentally obtained signals. We found that the minimum value for the evaluative function enabled us to estimate the intracellular diffusion coefficient and membrane permeability of the rat brain, which were corresponded to (1.3±0.1) × 10-3 mm2/sec and 66±24 μm/sec. Our method was useful for non-invasively estimating the cell-membrane permeability of biological tissues, and can easily be applied to human tissues and other samples.

Diffusion tensor tractography of the lower spinal cord

We employed a diffusion-tensor (DT) imaging technique involving a single-shot echo-planar sequence in combination with parallel imaging for tractography of the lower spinal cord and assessed the feasibility of this technique. Images were obtained at 1.5 T using a five-channel receiver coil. We used a single-shot echo-planar sequence with parallel imaging to acquire diffusion-weighted (DW) images in the axial plane with phase encoding in the right-left direction. A motion-probing gradient was applied in six directions with a b-value of 1,000 s/mm(2). The scan time was 5 min 15 s. On a reconstructed DW image in the sagittal plane, the spinal cord was included in a single region-of-interest to generate a tractogram of the entire cord in seven volunteers and nine patients with spinal canal stenosis or vertebral metastasis. In each subject, although the conus medullaris and cauda equina were continuously visualized, the cord was demonstrated as a bundle of tracts color-coded in the z-axis. Nerve roots were depicted showing color-coding in the x- and y-axes. In the patient group, displacement of the cord was depicted showing changes in the color of the cord. Displacement of the proximal nerve roots was also depicted in the two patients with vertebral metastasis. DT imaging using parallel imaging shows potential as a method for routine tractography of the lower spinal cord.