The evolution of the apparent diffusion coefficient in the pediatric brain at low and high diffusion weightings

PURPOSE: To evaluate the evolution of the apparent diffusion coefficient (ADC) with age for different degrees of diffusion weighting using a clinically feasible approach. MATERIALS AND METHODS: Data was acquired using separate scans with b values in the range typically used for clinical studies (100-900 seconds/mm(2)) and higher b values (1800-3000 seconds/mm(2)). The ADC was calculated for each of the data sets by fitting the data to a monoexponential function. RESULTS: The results from 50 children aged three years and less showed some deviations from literature values derived using a full biexponential fit, with these differences reflecting the approximations inherent in this approach. The values obtained with this technique appear to be reproducible but the resulting "institutional values" are comparable to those from other centers only if identical measurement criteria are used. CONCLUSION: A significant decline in both components of the ADC during the first few months of life was observed; in addition, the attenuated slow ADC values seen in adult white matter were only present at birth in early myelinating regions. The subsequent development of the slow ADC in white matter suggests that it is associated with myelination or processes associated with axonal development.     

ADC值评估腰椎间盘退变程度的研究

目的：探讨腰椎间盘表观扩散系数（ADC）测定评估退变程度,评价MR-DWI技术在腰椎间盘退变中的诊断价值。方法：对46例腰椎退行性病变患者及39例健康志愿者行MRI检查,获取各个椎间盘的修正Pfirrmann分级（共8级）及ADC值,分析两者的关系。同时将修正Pfirrmann分级分为正常（1～2级）、轻度退变（3～4级）、重度退变（5～8级）三组,分析ADC值与腰椎间盘退变程度的关系。结果：1级、2级椎间盘与其它各级椎间盘平均ADC值比较,差异均有高度统计学意义（P〈0．01）;3级椎间盘与4、5、6、7级椎间盘平均ADC值比较差异亦有统计学意义（P〈0．05）;4～8级椎间盘之间平均ADc值两两比较,差异无统计学意义（P〉0．05）。正常椎间盘、轻度及重度退变椎间盘平均ADC值比较,差异有高度统计学意义（P〈0．01）。正常和退变椎间盘的平均ADc值均与椎间盘部位有关。结论：ADC值可以较好地反映早期髓核退变程度,适用于早期椎间盘退变的追踪随访与观察。     

Influence of imaging parameters on the measurement of apparent diffusion coefficient

The apparent diffusion coefficient (ADC) values are calculated by using signal intensity in diffusion-weighted images (DWIs) with two or more different b-value. Therefore, the signal to noise ratio (SNR) of DWI with higher b-value may have a big influence on the measured ADC value. We examined the influence of the imaging parameters on the calculated ADC values. The SNR of DWI increased by using a larger voxel size, by means of a decreased number of matrix, an increased slice thickness, and an increased field of view (FOV). However, when the number of excitations was increased to improve the SNR of DWI, the signal intensity of background noise was observed to be slightly increased. It was suggested that the consistency of measured ADC was not preserved when the signal of the DWIs with higher b-value dropped close to the noise level.     

Assessment of lung development using hyperpolarized helium-3 diffusion MR imaging

PURPOSE: To determine whether hyperpolarized helium-3 (HHe) diffusion MR can detect the expected enlargement of alveoli that occurs with lung growth during childhood. MATERIALS AND METHODS: A total of 29 normal subjects aged four to 30 years underwent HHe diffusion MR imaging with the b-value pair 0, 1.6 second/cm(2). A second acquisition during a separate breathhold was performed using the b-value pair 0, 4 second/cm(2) to evaluate the dependence on b-value. The mean apparent diffusion coefficient (ADC) and lung volume for each acquisition and each subject was determined. RESULTS: Subjects as young as four years of age were able to cooperate with the imaging procedure. The mean ADC increased with increasing subject age (r = 0.8; P < 0.001), with a 55% increase in mean ADC from the youngest to oldest subject. Lung volumes measured on MR were highly repeatable for the two HHe MR acquisitions (r = 0.980, P < 0.001). The mean ADC values measured with the two different b-value pairs were highly correlated (r = 0.975; P < 0.001), but the higher b-value pair resulted in slightly lower mean ADCs (P < 0.001). CONCLUSION: HHe diffusion MR appears to detect the expected increase in alveolar size during childhood, and thus HHe MR may be a noninvasive method to assess development of the lung microstructure.     

Apparent diffusion coefficient in thoracolumbar intervertebral discs of healthy young volunteers

Apparent diffusion coefficient values (ADC) of healthy intervertebral discs of young volunteers in the thoracolumbar spine were determined using a single-shot EPI sequence. ADC(z) was in the lumbar spine slightly higher than ADC(x) or ADC(y). In vivo diffusion measurements of intervertebral discs may offer a novel diagnostic tool to evaluate disc diseases in early phases.     

Line scan diffusion weighted imaging (LSDI) on 0.2 Tesla MRI of the normal cervical cord in vivo: preliminary study

Diffusion weighted imaging(DWI) has been widely performed in the brain. However, DWI of the spinal cord is rarely performed because of technical and physiologic problems. Line scan diffusion weighted imaging(LSDI) is spin-echo based and relatively insensitive to susceptibility artifacts. We calculated the apparent diffusion coefficient(ADC) values of the normal cervical spinal cord by LSDI on a 0.2 Tesla MR imager and compared the ADC values with those from 1.5 Tesla MRI previously reported in the literature. The ADC values were adequate, and LSDI on 0.2 Tesla MRI is expected to become a useful tool for clinical application.     

Fat confounds the observed apparent diffusion coefficient in patients with hepatic steatosis

Purpose: Triglyceride signal contained in peaks near the water peak remains unsuppressed by conventional fat suppression techniques used in diffusion‐weighted imaging. In this work, we investigated the dependence of the apparent diffusion coefficient (ADC) on liver fat content and whether it is confounded by fat signal. Methods: 43 patients underwent liver diffusion‐weighted imaging (b = 0, 500 s/mm²) and single‐voxel MR‐spectroscopy. Proton density fat‐fraction (PDFF; range 0.23–34.5%) was measured from MR‐spectroscopy. A theoretical model was developed to account for the effects of fat on observed ADC, and used to correct the ADC. Linear correlation analysis was performed to assess the relationship between PDFF and ADC before and after correction. Results: Linear correlation analysis showed an inverse dependence between observed ADC and PDFF before correction (r² = 0.132; P = 0.017), and no dependence after correction (r² = 0.033; P = 0.24). Conclusion: The observed decrease in ADC in patients with fatty liver is, at least in part, artifactual due to residual fat signal near the water peak. Magn Reson Med, 2013. © 2012 Wiley Periodicals, Inc.     

小b 值表观扩散系数图监测子宫肌瘤高能聚焦超声后疗效的价值

目的：探讨小 b值表观扩散系数图(ADC maps)监测子宫肌瘤高能聚焦超声(HIFU)术后消融灶的价值。方法收集25例共34个子宫肌瘤患者进行HIFU治疗,所有患者术前、术后24 h内均行常规MRI、CE-T1 WI及b值分别取150、600、1000 s/mm2的单指数扩散加权成像(DWI)检查。采用单因素方差分析分析各b值术前、术后消融灶和残留未消融灶的平均ADC值变化。对各b值的ADC伪彩图消融灶与增强MRI的吻合度进行分级评定。结果 b值为150 s/mm2时,术后消融灶平均ADC值[(1.48±0.27)×10-3 mm2/s]低于术前[(2.06±0.21)×10-3 mm2/s]及残留未消融灶平均ADC值[(1.98±0.23)×10-3 mm2/s](P<0.05);b值为600、1000 s/mm2消融灶术前、术后ADC值以及残留未消融灶平均ADC值差异无统计学意义(P>0.05)。b值为150 s/mm2的ADC伪彩图消融灶与增强MRI的无灌注区域容积(non-perfused volume,NPV)有较高视觉吻合,优于 b 值为600、1000 s/mm2 ADC 图消融灶(P<0.05)。结论小b值(150 s/mm2)ADC图可间接反映子宫肌瘤HIFU治疗后的血供改变和消融范围,借此评估治疗效果。     

正常与退变腰椎间盘磁共振弥散加权成像的对比研究及其临床意义

目的：探讨磁共振弥散加权成像（DWI）及表观弥散系数测量值（ADC值）在腰椎间盘退变中的临床应用价值并对可能影响ADC值的相关因素进行分析。方法：对24例健康志愿者和16例腰腿痛患者进行常规T2WI及DWI扫描检查,进行相关研究。结果：正常腰椎间盘ADC值与年龄、性别、体重指数均无相关性。正常与退变椎间盘平均ADC值分别为（1.82±0.70）×10^-3mm^2/s和（1.22±0.27）×10^-3mm^2/s,正常与退变之间差异具有统计学意义。结论：弥散加权成像ADC测量值对退变椎间盘的诊断有一定的临床价值,利用磁共振弥散加权成像ADC值诊断退变椎间盘时可不考虑年龄、性别和体重指数的影响。     

Anisotropic diffusion in kidney: apparent diffusion coefficient measurements for clinical use

The purpose of this study was to evaluate anisotropy of the kidney by measurements of the apparent diffusion coefficient (ADC) using commercially available magnetic resonance (MR) imaging. Fifty-one consecutive patients underwent diffusion-weighted echoplanar MR imaging of the upper abdomen with five different strengths of motion probing gradients (b = 1.51, 55.3, 36.6, 317, and 932 sec/mm2) applied along the z-axis. Four ADC values for the upper pole and central portion of the kidney were calculated from four different b-value ranges and compared. The ADCs for the kidney calculated in the lower b-value ranges were significantly higher than those in the higher ranges. The ADCs for the upper pole portion were significantly higher than those for the central portion except for one in the highest b-value range. Diffusion in the kidney is anisotropic, probably due to the kidney's radially oriented structures such as renal vessels and tubules.     

Apparent diffusion coefficients and T2 relaxation time measurements to evaluate disc degeneration : A quantitative MR study of young patients with previous vertebral fracture

Purpose: To assess the suitability of apparent diffusion coefficient (ADC) measurements to evaluate degeneration processes of the vertebral disc and to compare the results with T2 relaxation time measurements in both degenerated and normal intervertebral discs.Material and Methods: Fourteen young patients (8.8-20.8 years old) who had had a vertebral compression fracture at least 1 year earlier, underwent MR studies with diffusion imaging in three orthogonal directions and T2 relaxation time measurements. ADC values and T2 relaxation times of both degenerated and normal intervertebral discs were compared to the values of 20 healthy young asymptomatic control subjects.Results: In the degenerated discs of patients, the ADC_x and ADC_y values were decreased compared to earlier determined values of healthy controls. ADC values in the z-direction in degenerated discs did not differ significantly from the values of controls. T2 relaxation times were shorter in the degenerated discs of patients compared to the values of controls. The greatest changes in both these values were observed in degenerated discs followed by discs with normal signal intensity adjacent to primary trauma area and secondary trauma area.Conclusion: We suggest that decreased ADC values reflect the lost integrity of the intervertebral disc. ADC measurements at MR may prove sensitive depicting of early degenerative changes in vertebral discs.     

Correlation of diffusion in lumbar intervertebral disks with occlusion of lumbar arteries: a study in adult volunteers.

PURPOSE: To evaluate the correlation of the diffusion values in lumbar intervertebral disks with lumbar artery status and the degree of disk degeneration. MATERIALS AND METHODS: Sagittal T2-weighted images of the lumbar spine were obtained in 37 asymptomatic volunteers aged 22-68 years. The apparent diffusion coefficient (ADC) of 98 lumbar intervertebral disks was determined, and two-dimensional time-of-flight magnetic resonance angiography was performed on the corresponding 98 lumbar artery pairs (total arteries = 196). The degree of disk degeneration and the status of lumbar arteries were evaluated independently by two radiologists. ADC calculations were performed on the basis of the average signal intensities of the selected region of interest in lumbar disks. The association between ADC values of disks, the disk degeneration, and the status of lumbar arteries of the same level were analyzed with analysis of covariance, and pairwise analysis between groups (Scheffé post hoc multiple comparison) was performed with statistical software. P values less than .01 were considered significant. RESULTS: The lumbar arterial status correlated strongly with the diffusion values of intervertebral disks, and the ADC values decreased with higher degrees of arterial narrowing. The correlation between disk degeneration and diffusion was not significant. Eight severely degenerated disks with normal lumbar artery status and diffusion values were found. CONCLUSION: Impaired flow in lumbar arteries is significantly associated with decreased diffusion in lumbar disks and may play an important role in disk degeneration.     

Noise correction for the exact determination of apparent diffusion coefficients at low SNR.

Noise in MR image data increases the mean signal intensity of image regions due to the usually performed magnitude reconstruction. Diffusion-weighted imaging (DWI) is especially affected by high noise levels for several reasons, and a decreasing SNR at increasing diffusion weighting causes systematic errors when calculating apparent diffusion coefficients (ADCs). Two different methods are presented to correct biased signal intensities due to the presence of complex noise: 1) with Gaussian intensity distribution, and 2) with arbitrary intensity distribution. The performance of the correction schemes is demonstrated by numerical simulations and DWI measurements on two different MR systems with different noise characteristics. These experiments show that noise significantly influences the determination of ADCs. Applying the proposed correction schemes reduced the bias of the determined ADC to less than 10% of the bias without correction. Magn Reson Med 45:448-453, 2001.     

Assessment of apparent diffusion coefficient in normal and degenerated intervertebral lumbar disks: initial experience

PURPOSE: To determine prospectively the diffusibility of water in normal lumbar disks in adults by using the mean apparent diffusion coefficient (ADC) and to determine if a relationship exists between disk ADC and magnetic resonance (MR) findings of disk degeneration. MATERIALS AND METHODS: The study was approved by the Institutional Review Board, and all participants gave written informed consent prior to enrollment. Diffusion-weighted MR imaging of the lumbar spine was performed in 39 patients (all men; mean age, 53 years) and five volunteers (all men; mean age, 31 years). ADC values were recorded for each disk. All disks were visually graded by two independent observers as being normal or as showing at least one of three MR findings of degeneration on sagittal T2-weighted images. Mean ADC values of normal disks were compared with those of degenerated disks and were correlated with age and anatomic location. Data were analyzed by using Kendall correlation statistics, Mantel-Haenszel statistics, and a paired two-tailed Student t test. RESULTS: The mean ADC value was 2.27 x 10(-3) mm(2)/sec +/- 0.58 (+/- standard deviation) in normal disks and 2.06 x 10(-3) mm(2)/sec +/- 0.47 in abnormal disks (9% reduction, P = .006). A statistically significant dependence of lumbar disk ADC on anatomic location was reported (analysis of variance, P < .001), with lower ADC values seen in more caudal disks. There was no association between age and mean disk ADC. CONCLUSION: A statistically significant decrease was seen in the ADC values of degenerated lumbar disks when compared with ADC values of normal disks. More caudal disks, even when normal, showed lower ADC values than more cephalic disks.     

Double line scan diffusion imaging

A new double line scan diffusion imaging sequence (DLSDI) is presented. In DLSDI, two lines from two separate slices are acquired in each shot. As its predecessor, LSDI, DLSDI is insensitive to motion artifacts and it can be used on conventional MR scanners. In addition, DLSDI is almost twice as fast as LSDI. Preliminary results from phantom and patient studies show excellent agreement between ADC trace maps obtained with DLSDI and LSDI. The technical and the theoretical aspects of DLSDI are studied, and it is shown how the conditional random walk model can be used as an analytical tool to derive the diffusion sensitivity in the DLSDI sequence.     

MRI表观弥散系数值在鉴别急慢性腰椎间盘损伤的应用研究

目的 评价磁共振弥散加权成像表观弥散系数（ADC）在鉴别腰椎间盘急、慢性损伤的应用价值.方法 回顾性分析行腰椎间盘磁共振检查男性患者175例,扫描序列为矢状位T1WI、T2WI、T2WI-SPAIR、DWI及轴位T2 WI;选取Pfirrmann分级Ⅲ/Ⅳ级腰4/5及腰5/骶1椎间盘为研究对象,共262个椎间盘（88个Ⅱ/Ⅴ级椎间盘未纳入研究）;Ⅲ级133个椎间盘,急、慢性损伤组及退变组分别44、44及45个;Ⅳ级129个椎间盘,急、慢性损伤组及退变组分别43、44及42个;分别测量各椎间盘ADC值并进行统计学分析.结果 PfirrmannⅢ级椎间盘急、慢性损伤组及退变组间ADC值差异有统计学意义（P＜0.05）,两两比较差异有统计学意义（P＜0.05）,急性组最大,退变组次之,慢性组最小;Ⅳ级椎间盘急、慢性损伤组及退变组间差异有统计学意义（P＜0.05）,两两比较慢性损伤组与退变组差异无统计学意义（P＞0.05）,急性损伤组与慢性损伤组及退变组间差异有统计学意义（P＜0.05）,且急性损伤组ADC值大于慢性损伤组与退变组.PfirrmannⅢ级各组椎间盘ADC值均高于对应Ⅳ级各组,且差异有统计学意义（P＜0.05）.结论 MRI表观弥散系数值能为椎间盘急慢性损伤的鉴别诊断提供依据.     

DTI及T2 mapping对腰椎间盘退变的诊断价值

目的：探讨磁共振扩散张量成像(DTI)表观扩散系数(ADC)、各向异性分数(FA)以及 T2 mapping T2值定量评估腰椎间盘退变程度的价值。方法健康志愿者12例,男8例,女4例;慢性下腰痛患者28例,男15例,女13例;年龄19~70岁。行腰椎MRI矢状位T2 WI、DTI、T2 mapping成像。对 L1~S1椎间盘进行Pfirrminn退变分级,测量各腰椎间盘髓核 ADC 值、FA 值以及T2值并分析其与不同腰椎间盘退变分级的相关性,比较 ADC值、FA值以及T2值对腰椎间盘退变的诊断价值。结果腰椎间盘的平均ADC值、T2值与Pfirrminn分级呈显著负相关关系,相关系数分别为r=-0.779,r=-0.708(P<0.001);FA值与Pfirrminn分级呈正相关关系,但是相关关系不密切(相关系数r=0.474,P<0.001)。结论 DTI和T2 mapping可以定量评估腰椎间盘的退变程度,其诊断价值为 ADC 值最高,T2值次之,FA 值较差。     

MR line scan diffusion imaging of the brain in children

BACKGROUND AND PURPOSE: MR imaging of the self-diffusion of water has become increasingly popular for the early detection of cerebral infarction in adults. The purpose of this study was to evaluate MR line scan diffusion imaging (LSDI) of the brain in children. METHODS: LSDI was performed in four volunteers and 12 patients by using an effective TR/TE of 2736/89.4 and a maximum b value of 450 to 600 s/mm2 applied in the x, y, and z directions. In the volunteers, single-shot echo planar imaging of diffusion (EPID) was also performed. The patients (10 boys and two girls) ranged in age from 2 days to 16 years (average age, 6.6 years). Diagnoses included acute cerebral infarction, seizure disorder, posttraumatic confusion syndrome, complicated migraine, residual astrocytoma, encephalitis, hypoxia without cerebral infarction, cerebral contusion, and conversion disorder. In all patients, routine spin-echo images were also acquired. Trace images and apparent diffusion coefficient maps were produced for each location scanned with LSDI. RESULTS: In the volunteers, LSDI showed less chemical-shift and magnetic-susceptibility artifact and less geometric distortion than did EPID. LSDI was of diagnostic quality in all studies. Diffusion abnormalities were present in five patients. Restricted diffusion was present in the lesions of the three patients with acute cerebral infarction. Mildly increased diffusion was present in the lesions of encephalitis and residual cerebellar astrocytoma. No diffusion abnormalities were seen in the remaining seven children. CONCLUSION: LSDI is feasible in children, provides high-quality diffusion images with less chemical-shift and magnetic-susceptibility artifact and less geometric distortion than does EPID, and complements the routine MR examination.     

Quantitative and diffusion MR imaging as a new method to assess osteoporosis

BACKGROUND AND PURPOSE: The role of advanced MR imaging techniques in demonstrating the microarchitectural changes in osteoporosis has been recently investigated. Our aim was to determine the role of quantitative and diffusion MR imaging in the diagnosis of osteoporosis compared with dual-energy x-ray absorptiometry (DEXA). MATERIALS AND METHODS: Fifty-one subjects underwent both DEXA and conventional MR imaging with diffusion and apparent diffusion coefficient (ADC) mapping. T1, T2, diffusion signal intensity, and ADC values were calculated and compared with bone mineral attenuation (BMD). Results were obtained from L1 to L4 of each patient with a total of 204 lumbar vertebrae. RESULTS: Both T1 and T2 signal intensities tended to increase when both diffusion and ADC values decreased with reducing BMD. CONCLUSIONS: An inverse relationship between BMD and T1 and T2 signal intensities and a direct relationship between diffusion and ADC values were present in this pilot group. The T1/diffusion signal-intensity ratio could be a reliable diagnostic indicator of osteoporosis.     

不同b值和扩散张量成像导出量的定量关系研究

目的　探索不同b值和扩散张量成像参数的定量关系。方法　对 12例正常成人进行扩散张量磁共振扫描 ,测量多个灰白质感兴趣区的表观扩散系数 (ADC)、指数表观扩散系数 (EADC)、最大特征值、各向异性比率 (FA)、各向异性指数 (AI)和相对各向异性 (RA)等参数 ,分析这些参数随着b值的变化趋势。结果　FA和RA的平均值、中位数、标准差以及变异系数都不随b值变化 (P >0 5 ) ;而ADC、EADC及最大特征值受b值的影响 (P <0 0 1) ,随b值的增加而降低 ;AI的平均值、中位数、标准差及变异系数在不同被试者间差异存在显著性意义 (P <0 0 5 )。结论　b值确实影响多个扩散张量成像的导出量。在临床应用中当比较不同被试者 ,或者不同组织结构时 ,应尽量选择同样的成像参数 ,特别是b值 ,同时选择不受b值影响的参数 ,如FA和RA。