轻型创伤性脑损伤脑白质纤维束扩散张量成像研究

目的：使用3.0T 磁共振扩散张量成像(DTI)技术观察轻型创伤性脑损伤(mTBI)患者脑白质纤维束的改变,探讨 DTI对 mTBI 的临床诊断价值。方法选取30例 mTBI 患者及30例健康对照者分别进行常规 CT、MRI 及 DTI 检查,分别测量 mTBI患者(急性期、亚急性期、伤后5周~3个月)和对照者的胼胝体膝部、压部、双侧内囊前后肢、扣带束、上纵束、下纵束的各向异性(FA)值、表观扩散系数(ADC)值,观察各测量值的变化规律。结果mTBI 患者部分脑白质纤维束区的 FA 值在急性期、亚急性期减低(P 均<0.05),伤后5周~3个月时仍低于对照者(P 均<0.05),但胼胝体膝部及压部的 FA 值在急性期不减低反而升高(P 均>0.05),此后呈逐渐减低趋势,并在外伤5周~3个月时略低于正常对照组,但差异无统计学意义(P 均>0.05)。急性期、亚急性期 mTBI 患者的 ADC 值低于正常对照组,并在外伤5周~3个月时接近或略高于对照组,但差异无统计学意义(P 均>0.05)。结论DTI 对 mTBI 敏感性较高,能够准确显示白质纤维束的损伤情况并使其可视化,DTI 对 mTBI 的诊断具有重要的临床价值。     

Prostate cancer vs. post‐biopsy hemorrhage: Diagnosis with T2‐ and diffusion‐weighted imaging

Purpose:

To assess the value of quantitative T2 signal intensity (SI) and apparent diffusion coefficient (ADC) to differentiate prostate cancer from post‐biopsy hemorrhage, using prostatectomy as the reference.

Materials and Methods:

Forty‐five men with prostate cancer underwent prostate magnetic resonance imaging (MRI), including axial T1‐weighted imaging (T1WI), T2WI, and single‐shot echo‐planar image (SS EPI) diffusion‐weighted imaging. Two observers measured, in consensus, normalized T2 signal intensity (SI) (nT2, relative to muscle T2 SI), ADC, and normalized ADC (nADC, relative to urine ADC) on peripheral zone (PZ) tumors, benign PZ hemorrhage, and non‐hemorrhagic benign PZ. Tumor maps from prostatectomy were used as the reference. Mixed model analysis of variance was performed to compare parameters among the three tissue classes, and Pearson's correlation coefficient was utilized to assess correlation between parameters and tumor size and Gleason score. Receiver‐operating characteristic (ROC)‐curve analysis was used to determine the performance of nT2, ADC, and nADC for diagnosis of prostate cancer.

Results:

nT2, ADC, and nADC were significantly lower in tumor compared with hemorrhagic and non‐hemorrhagic benign PZ (P < 0.0001). There was a weak but significant correlation between ADC and Gleason score (r = ?0.30, P = 0.0119), and between ADC and tumor size (r = ?0.40, P = 0.0027), whereas there was no correlation between nT2 and Gleason score and tumor size. The areas under the curve to distinguish tumor from benign hemorrhagic and non‐hemorrhagic PZ were 0.97, 0.96, and 0.933 for nT2, ADC, and nADC, respectively.

Conclusion:

Quantitative T2 SI and ADC/nADC values may be used to reliably distinguish prostate cancer from post‐biopsy hemorrhage. J. Magn. Reson. Imaging 2010;31:1387–1394. © 2010 Wiley‐Liss, Inc.

     

Separating changes in the intra- and extracellular water apparent diffusion coefficient following focal cerebral ischemia in the rat brain.

Selective intracellular (IC) and extracellular (EC) brain water apparent diffusion coefficient (ADC) values were measured in normal and ischemic rat brain. Selective T(1)-relaxation enhancement of the EC water, using intracerebroventricular (ICV) infusion of an NMR contrast reagent (CR), was used to separate the IC and EC signal contributions. In the CR-infused, normal brain (n = 4), T(1) = 235 +/- 10 ms and T(2) = 46 +/- 2 ms for IC water (85%) and T(1) = 48 +/- 8 ms and T(2) = 6 +/- 2 ms for EC water (15%). Volume-localized ADC(z) (z-gradient axis) values were 0.90 +/- 0.02 (EC+IC), 0.81 +/- 0.05 (IC), 0.51 +/- 0.02 (EC+IC), and 0.53 +/- 0.07 (IC), for normal, CR-infused, ischemic, and ischemic/CR-infused groups, respectively (ADC values are x10(-3) mm(2)/s; n = 5 for each group). Imaging ADC(z) values were 0.81 +/- 0.03 (EC+IC), 0.75 +/- 0.05 (IC), 0.51 +/- 0.04 (EC+IC), and 0.52 +/- 0.05 (IC), respectively, for the same groups. Imaging ADC(av) (average diffusivity) values for the same groups were 0.70 +/- 0.05 (EC+IC), 0.69 +/- 0.06 (IC), 0.45 +/- 0.06 (EC+IC), and 0.44 +/- 0.06 (IC), respectively. These results suggest that the IC water ADC determines the overall water ADC value in normal and ischemic rat brain.     

Effect of shot number on the calculated apparent diffusion coefficient in phantoms and in human liver in diffusion‐weighted echo‐planar imaging

Purpose

To show the signal intensity varies with shot number in diffusion‐weighted (DW) echo‐planar imaging (EPI) and affects apparent diffusion coefficient (ADC) calculation.

Materials and Methods

This prospective study was performed on 35 adult patients and 20 volunteers. Measurements were made on a 3T scanner using a breathhold DW spin‐echo EPI (SE EPI) sequence. Three protocols were used: A) eight consecutive shots at a fixed b‐value of 0 seconds/mm² with TR = 1000 and 3000 msec; B) seven consecutive shots at b‐values = 0, 1000, 750, 500, 250, 100, 0 seconds/mm² (in that order) with TR = 3500 msec; and C) seven consecutive shots (as in B) with TR = 1000, 1750, and 7000 msec.

Results

For protocol A, signal intensity decreased significantly from the first to second shot (P<0.0001) and thereafter remained constant. For protocol B, the ADC depended on which b = 0 seconds/mm² image was used. Using the first b = 0 seconds/mm², the mean ADC was 15% higher than using the second b = 0 seconds/mm² (P<0.0001). For protocol C, the difference between ADC using the first b = 0 seconds/mm² and the second b = 0 seconds/mm² decreased as the TR increased.

Conclusion

The signal intensity can vary with shot number in SE EPI. For TR ≥ 3000 msec, steady‐state is attained after one shot. Using data acquired prior to steady‐state confounds the calculation of ADC values. J. Magn. Reson. Imaging 2009;30:547–553. © 2009 Wiley‐Liss, Inc.     

Comparison of apparent diffusion coefficients and distributed diffusion coefficients in high‐grade gliomas

Purpose:

To compare apparent diffusion coefficients (ADCs) with distributed diffusion coefficients (DDCs) in high‐grade gliomas.

Materials and Methods:

Twenty patients with high‐grade gliomas prospectively underwent diffusion‐weighted MRI. Traditional ADC maps were created using b‐values of 0 and 1000 s/mm². In addition, DDC maps were created by applying the stretched‐exponential model using b‐values of 0, 1000, 2000, and 4000 s/mm². Whole‐tumor ADCs and DDCs (in 10^?3 mm²/s) were measured and analyzed with a paired t‐test, Pearson's correlation coefficient, and the Bland‐Altman method.

Results:

Tumor ADCs (1.14 ± 0.26) were significantly lower (P = 0.0001) than DDCs (1.64 ± 0.71). Tumor ADCs and DDCs were strongly correlated (R = 0.9716; P < 0.0001), but mean bias ± limits of agreement between tumor ADCs and DDCs was ?0.50 ± 0.90. There was a clear trend toward greater discordance between ADC and DDC at high ADC values.

Conclusion:

Under the assumption that the stretched‐exponential model provides a more accurate estimate of the average diffusion rate than the mono‐exponential model, our results suggest that for a little diffusion attenuation the mono‐exponential fit works rather well for quantifying diffusion in high‐grade gliomas, whereas it works less well for a greater degree of diffusion attenuation. J. Magn. Reson. Imaging 2010;31:531–537. © 2010 Wiley‐Liss, Inc.

     

Neuroimaging assessment of memory‐related brain structures in a rat model of acute space‐like radiation

Purpose

To investigate the acute effects on the central nervous system (CNS) of ⁵⁶Fe radiation, a component of high‐energy charged particles (HZE) in space radiation, using quantitative magnetic resonance imaging (MRI) noninvasively.

Materials and Methods

Sprague–Dawley rats were exposed to whole‐brain ⁵⁶Fe (0, 1, 2, and 4 Gy). At 1 week postirradiation, MRI scans were made using T2‐weighted (T2WI), diffusion‐weighted (DWI), and contrast enhanced T1‐(CET1) imaging. T2 relaxation time and apparent diffusion coefficient (ADC) values were obtained from memory‐related brain regions of interest (ROIs). Histopathology was correlated using ex vivo tissues.

Results

No overt abnormalities were visualized using T2WI and DWI at 1 week postradiation. CET1 values did not differ significantly between the irradiated and control animals. Compared to 0 Gy, there were significant prolongations in T2 values and reductions in ADC after irradiation. In the absence of evident neuronal pathology, immunohistochemistry revealed astrocytic activation in 4 Gy animals.

Conclusion

At 1 week after whole‐brain ⁵⁶Fe exposure, T2 and ADC values can differentiate radiosensitivity in regions critical for hippocampal‐related memory. MRI may provide noninvasive assessment of the initial molecular/cellular disturbances in vivo after HZE irradiation. J. Magn. Reson. Imaging 2009;29:785–792. © 2009 Wiley‐Liss, Inc.     

Combined T2‐weighted and diffusion‐weighted MRI for diagnosis of urinary bladder invasion in patients with prostate carcinoma

Purpose

To retrospectively determine the diffusion‐weighted imaging (DWI) characteristics and apparent diffusion coefficient (ADC) values of prostate carcinoma (PCa) with urinary bladder invasion, and to compare the accuracy of T2‐weighted MRI alone and T2 combined with DWI for predicting urinary bladder invasion.

Materials and Methods

Sixty‐eight patients with proven PCa were diagnosed with urinary bladder invasion after conventional magnetic resonance imaging (MRI) and DWI (b value = 750 sec/mm²) examinations. All the 68 cases underwent cystoscopy examination. DWI appearances of all urinary bladder invasion and a normal urinary bladder wall were analyzed, and their ADC values were measured. T2 images alone and then T2 images combined with DWI were scored for the likelihood of urinary bladder invasion on the basis of radiologists' written reports. The area under the receiver operating characteristic curve (AUC) was used to assess accuracy. Statistical significance was inferred at P < 0.05.

Results

After cystoscopy examination, 45 (66%) of 68 cases were pathologically proven urinary bladder invasion. The mean ADCs for urinary bladder invasion and normal urinary bladder wall were (0.963 ± 0.155) × 10^?3mm²/sec and (1.517 ± 0.103) × 10^?3mm²/sec, respectively. The ADC values of urinary bladder invasion were significantly lower than those of normal urinary bladder wall (P = 0.000). The AUC for T2‐weighted imaging plus DW imaging (0.861) was significantly larger than that for T2‐weighted imaging alone (0.734) or for DW imaging alone (0.703) (P < 0.001).

Conclusion

Urinary bladder invasion had lower ADC values compared with normal urinary bladder wall. T2 images plus DWI is significantly better than T2‐weighted imaging alone in the detection of urinary bladder invasion in patients with PCa. J. Magn. Reson. Imaging 2009. © 2009 Wiley‐Liss, Inc.

     

Diffusion‐weighted imaging of the healthy pancreas: ADC values are age and gender dependent

Purpose:

To investigate the healthy pancreas with diffusion‐weighted imaging (DWI) for characterization of age and gender‐related differences in apparent diffusion coefficient (ADC) values.

Materials and Methods:

Sixty six volunteers were prospectively enrolled (33 male, 33 female; range 1.4 to 83.7 years of age) and echo‐planar DWI of the pancreas was performed. ADC values were measured in the pancreas head, body, and tail using a pixel‐by‐pixel approach. Effects of age and gender on ADC values were analyzed using a two‐factorial multivariate analysis of variance (MANOVA).

Results:

ADC values correlated inversely with the age of the volunteers. The mean global pancreatic ADC values (× 10^?3 mm²/s) in the age groups 0–20 years, 21–40 years, and > 40 years were 1.18 ± 0.19, 1.07 ± 0.13, and 0.99 ± 0.18, respectively. Female individuals had higher mean global ADC values than male (1.13 ± 0.14 versus 1.02 ± 0.18 × 10^?3 mm²/s). MANOVA showed significant effects of age (P value 0.022, eta² = 0.13) and gender (P value 0.001, eta² = 0.28) on ADC values.

Conclusion:

Pancreatic ADC values decline with ageing and show significant gender differences with higher mean values in females. The awareness of baseline values adjusted to age and gender will be important for correct interpretation of individual cases and design of future studies. J. Magn. Reson. Imaging 2013;37:886–891. © 2012 Wiley Periodicals, Inc.

     

Evaluation of therapeutic response to concurrent chemoradiotherapy in patients with cervical cancer using diffusion‐weighted MR imaging

Purpose:

To investigate the changes in apparent diffusion coefficients (ADCs) in cervical cancer patients receiving concurrent chemoradiotherapy (CCRT), and to assess the relationship between tumor ADCs or changes in tumor ADCs and final tumor responses to therapy.

Materials and Methods:

Twenty‐four patients with cervical cancer who received CCRT were examined with 3 Tesla (T) MRI including diffusion‐weighted imaging (DWI). All patients had three serial MR examinations: before therapy (pre‐Tx); at 4 weeks of therapy (mid‐Tx); and 1 month after completion of therapy (post‐Tx). At each examination, ADC was measured in tumors and normal gluteus muscles. Final tumor response as determined by change in tumor size or volume using MRI was correlated with tumor ADCs at each therapeutic time or changes in tumor ADCs at mid‐Tx.

Results:

From pre‐Tx to post‐Tx, mean tumor ADCs were 0.88, 1.30, and 1.47 × 10^?3 mm²/s in sequence (P < 0.001), while those of normal gluteus muscles were 1.24, 1.29, and 1.21 × 10^?3 mm²/s in sequence (P > 0.05). At mid‐Tx, tumor ADCs and changes in tumor ADCs had a significant correlation with final tumor size responses (P = 0.029 and 0.025, respectively). However, the tumor ADC values at pre‐Tx were not associated with the final tumor size response (P = 0.47). The final tumor volume response was not associated with tumor ADC at pre‐Tx or mid‐Tx (P > 0.05) or changes in tumor ADCs at mid‐Tx (P > 0.05).

Conclusion:

DWI may have potentials in evaluating the therapeutic response to CCRT in patients with cervical cancer. J. Magn. Reson. Imaging 2013;37:187–193. © 2012 Wiley Periodicals, Inc.

     

Motion artifact reduction of diffusion‐weighted MRI of the liver: Use of velocity‐compensated diffusion gradients combined with tetrahedral gradients

Purpose:

To assess the effect of motion artifact reduction on the diffusion‐weighted magnetic resonance imaging (DWI‐MRI) of the liver, we compared velocity‐compensated DWI (VC‐DWI) and VC‐DWI combined with tetrahedral gradients (t‐VC‐DWI) to conventional DWI (c‐DWI) in the assessment of apparent diffusion coefficients (ADCs) of the liver.

Materials and Methods:

In 12 healthy volunteers, the liver was scanned with c‐DWI, VC‐DWI, and t‐VC‐DWI sequences. The signal‐to‐noise ratio (SNR) and ADC of the liver parenchyma were measured and compared among sequences.

Results:

The image quality was visually better for t‐VC‐DWI than for the others. The SNR for t‐VC‐DWI was significantly higher than that for VC‐DWI (P < 0.05) and comparable to that for c‐DWI. ADCs in both hepatic lobes were significantly lower for t‐VC‐DWI than for c‐DWI (P < 0.01). ADC in the left lobe was significantly lower for VC‐DWI than for c‐DWI (P < 0.01). Although ADC in the left lobe was significantly higher for c‐DWI (P < 0.01), no significant differences in ADCs were found between the right and left lobes for VC‐DWI and t‐VC‐DWI.

Conclusion:

The use of a t‐VC‐DWI sequence enables us to correct ADCs of the liver for artificial elevation due to cardiac motion, with preserved SNR. J. Magn. Reson. Imaging 2013;37:172–178. © 2012 Wiley Periodicals, Inc.     

Dual‐source parallel RF transmission for diffusion‐weighted imaging of the abdomen using different b values: Image quality and apparent diffusion coefficient comparison with conventional single‐source transmission

Purpose:

To prospectively and intraindividually evaluate what effects dual‐source parallel radiofrequency (RF) transmission have on image quality and apparent diffusion coefficient (ADC) of abdomen diffusion‐weighted imaging (DWI) using different b values, compared with the single‐source RF transmission.

Materials and Methods:

Eighteen healthy male volunteers were enrolled in this Health Insurance Portability and Accountability Act (HIPAA)‐compliant Institutional Review Board (IRB)‐approved study. Abdominal DWI was performed with dual‐source and single‐source RF transmission at 3.0 T using a series of b‐value combinations: 0/100, 0/500, 0/800, and 0/100/800. RF field homogeneity, subjective image quality, and signal to noise ratio (SNR) of each abdominal organ were evaluated. ADC values were calculated for each abdominal organ. Wilcoxon test and repeated‐measures analysis of variance was used to calculate statistical significance.

Results:

The parallel RF transmission significantly improved homogeneity of the RF field (P = 0.0001–0.008) and subjective image quality (P < 0.0001) at each b value and also increased SNR. At lower and higher b value, the measured ADC of lateral left hepatic lobe and spleen between dual‐source and single‐source images were significantly different (P = 0.0001–0.047). At b = 0/500, there was no significant difference in ADC measurements between dual‐source and single‐source RF transmission for abdominal organs, except a slight statistically significant difference for spleen (P = 0.047).

Conclusion:

Parallel RF transmission significantly improved the image quality and homogeneity of the RF field. The RF transmission had a significant influence on measured ADC of lateral left hepatic lobe and spleen. At b = 0/500 the influence was minimum for all abdominal organs. J. Magn. Reson. Imaging 2013;37:875–885. © 2012 Wiley Periodicals, Inc.