High-b diffusivity of MS lesions in cervical spinal cord using ultrahigh-b DWI (UHb-DWI)

PURPOSE

The purpose of this study was to investigate UHb-rDWI signal in white matter tracts of the cervical spinal cord (CSC) and compare quantitative values between healthy control WM with both MS NAWM and MS WM lesions.

METHODS

UHb-rDWI experiments were performed on (a) 7 MS patients with recently active or chronic lesions in CSC and on (b) 7 healthy control of similar age range and gender distribution to MS subjects. All MRI data were acquired using clinical 3T MRI system. Axial high-b diffusion images were acquired using 2D single-shot DW stimulated EPI with reduced FOV and a CSC-dedicated 8 channel array coil. High-b diffusion coefficient DH was estimated by fitting the signal-b curve to a double or single-exponential function.

RESULTS

The high-b diffusivity DH values were measured as (0.767 ± 0.297) × 10-3 mm2/s in the posterior column lesions, averaged over 6 MS patients, and 0.587 × 10-3 mm2/s in the corticospinal tract for another patient. The averaged DH values of the 7 healthy volunteers from the posterior and lateral column were (0.0312 ± 0.0306) × 10-3 and (0.0505 ± 0.0205) × 10-3 mm2/s, respectively. UHb-rDWI signal-b curves of the MS patients revealed to noticeably behave differently to that of the healthy controls. The patient signal-b curves decayed with greater high-b decay constants to reach lower signal intensities relative to signal-b curves of the healthy controls.

CONCLUSION

UHb-DWI of the CSC reveals a marked difference in signal-b-curves and DH values in MS lesions compared to NAWM and healthy control WM. Based on physical principles, we interpret these altered observations of quantitative diffusion values to be indicative of demyelination. Further studies in animal models will be required to fully interpret UHb-DWI quantitative diffusion values during demyelination and remyelination.

High signal renal tumors on DWI: the diagnostic value of morphological characteristics

PURPOSE

To assess the usefulness of morphological characteristics of diffusion-weighted imaging (DWI) for differentiating malignant renal tumors from benign renal tumors, and clear cell renal cell carcinoma (RCC) from non-clear cell RCC at 3.0 T.

METHODS

The study included 249 patients with 251 histopathologically confirmed renal tumors that showed high signal on DWI. For each tumor, two radiologists independently evaluated apparent diffusion coefficient (ADC) values and morphological characteristics of DWI. The differences in the quantitative and qualitative magnetic resonance imaging (MRI) features determined by the readers were assessed. The ADC values between malignant and benign renal tumors and between clear cell and non-clear cell RCC were compared using Mann-Whitney tests. The proportional differences of morphological characteristics of DWI between malignant and benign renal tumors and between clear cell and non-clear cell RCC were compared using Chi-square tests.

RESULTS

There were no significant differences in the quantitative and qualitative MRI features determined by the readers. The ADC values for malignant renal tumors were statistically significantly higher than those for benign renal tumors (p < 0.05), and the ADC values for clear cell RCC were statistically significantly higher than those for non-clear cell RCC (p < 0.05). The proportion of morphological characteristics of DWI between malignant and benign renal tumors was statistically significantly different at ring, nodular, flaky high signal. The proportion of morphological characteristics of DWI between clear cell and non-clear cell RCC was statistically significantly different at uniform high signal.

CONCLUSIONS

The morphological characteristics of DWI are useful in differentiating renal tumors.

Measurement and scan reproducibility of parameters of intravoxel incoherent motion in renal tumor and normal renal parenchyma: a preliminary research at 3.0 T MR

PURPOSE

To prospectively estimate measurement and scan reproducibility of parameters of intravoxel incoherent motion (IVIM) in renal tumors, normal renal cortex, and medulla.

METHODS

Twenty-four consecutive patients (twelve males and twelve females; median age 56.7 years, range 32-71 years) with 25 renal tumors (20 renal cell carcinomas, one urothelium carcinoma, three angiomyolipomas, and one oncocytoma) were examined twice using IVIM₁ and IVIM₂ with 9 and 16 b values, respectively, at 3.0 T. All the patients were re-scanned in 24-48 h. Regions of interest (ROIs) were placed in solid part of tumor, normal cortex, and medulla to derive IVIM parameters D (true diffusion coefficient), D* (pseudodiffusion coefficient), and f (perfusion fraction of pseudodiffusion). Differences in parameters between two IVIM sets and intra-observer, inter-observer, and scan-rescan differences were assessed using paired t tests. Intra-observer, inter-observer, and scan-rescan reproducibility were assessed by measuring coefficient of variation and Bland-Altman limits of agreements.

RESULTS

Intra-observer reproducibility of renal tumors, normal renal cortex, and medulla was excellent for apparent diffusion coefficient (ADC; CV: 3.45%-5.34%, BA-LA: -14% to 18%) and D (CV: 3.65% to 6.04%, BA-LA: -18% to 19%), good for f (CV: 11.96%-16.08%, BA-LA: -76.4% to 92.1% except f of medulla with CV of 32.59% and BA-LA of -76.4% to 92.1% in IVIM₁), and poor for D* (CV: 25.0% to 75.4%, BA-LA: -111% to 150%). The same order was in inter-observer reproducibility analysis. Scan-rescan reproducibility was the worst of the three parameters. Renal medulla showed worse reproducibility than renal tumors and the normal cortex. The metrics of IVIM₂ had better reproducibility than IVIM₁.

CONCLUSION

Excellent reproducibility evaluation for ADC and D, good for f, and poor for D* derived from IVIM was performed in renal tumors, normal renal cortex, and medulla. D* has limited reliability and scan-rescan reproducibility should be improved.