Improvement of renal diffusion-weighted magnetic resonance imaging with readout-segmented echo-planar imaging at 3T

Probing Renal Microstructure and Function with Advanced Diffusion MRI: Concepts, Applications, Challenges, and Future Directions

Diffusion measurements in the kidney are affected not only by renal microstructure but also by physiological processes (i.e., glomerular filtration, water reabsorption, and urine formation). Because of the superposition of passive tissue diffusion, blood perfusion, and tubular pre-urine flow, the limitations of the monoexponential apparent diffusion coefficient (ADC) model in assessing pathophysiological changes in renal tissue are becoming apparent and motivate the development of more advanced diffusion-weighted imaging (DWI) variants. These approaches take advantage of the fact that the length scale probed in DWI measurements can be adjusted by experimental parameters, including diffusion-weighting, diffusion gradient directions and diffusion time. This forms the basis by which advanced DWI models can be used to capture not only passive diffusion effects, but also microcirculation, compartmentalization, tissue anisotropy. In this review, we provide a comprehensive overview of the recent advancements in the field of renal DWI. Following a short introduction on renal structure and physiology, we present the key methodological approaches for the acquisition and analysis of renal DWI data, including intravoxel incoherent motion (IVIM), diffusion tensor imaging (DTI), non-Gaussian diffusion, and hybrid IVIM-DTI. We then briefly summarize the applications of these methods in chronic kidney disease and renal allograft dysfunction. Finally, we discuss the challenges and potential avenues for further development of renal DWI. LEVEL OF EVIDENCE: 5 TECHNICAL EFFICACY: Stage 2.

Readout-segmented diffusion weighted imaging of the testis at 3.0 T: comparison with single-shot echo-planar imaging

OBJECTIVE

The current study aimed to explore the feasibility of readout-segmented echo-planar imaging (RS-EPI) of the testis at 3.0 T, by comparing with single-shot echo-planar imaging (SS-EPI) in qualitative image quality and quantitative apparent diffusion coefficient (ADC) values.

METHODS

66 patients undergoing scrotal MRI for various clinical indications were included retrospectively. RS-EPI image quality was rated from 1 (severe distortion or artifact, or nondiagnostic) to 4 (nearly no distortion or artifact, or outstanding). The comparative image quality (RS- vs. SS-EPI) was rated from - 2 (SS-EPI severe or greater conspicuity) to 2 (RS-EPI severe or greater conspicuity). The confidence interval of proportions (CIOP) of comparative image quality and Wilcoxon rank sum test were performed to assess the preferences between RS-EPI and SS-EPI. Paired samples t-test and Bland-Altman analysis were performed to compare the mean ADC values of RS-EPI and SS-EPI. The mean, maximum, and minimum ADC values measured by RS-EPI were compared in normal testicular parenchyma, benign and malignant intratesticular lesions.

RESULTS

The evaluation of RS-EPI image quality showed RS-EPI with the characteristics of slight geometric distortion and susceptibility artifact, and good lesion conspicuity. The assessment of comparative image quality showed SS-EPI with obvious geometric distortion and susceptibility artifact, and RS-EPI preferred in lesion conspicuity. The CIOP ranged from 97 to 100% among three readers, with preferring to RS-EPI improving image quality (P < 0.001). There was a strong correlation and good agreement between mean ADC values measured by RS-EPI and SS-EPI. The mean, maximum and minimum ADC values by RS-EPI were significantly different in normal testicular parenchyma, benign and malignant intratesticular lesions.

CONCLUSION

RS-EPI DWI of the testis improved image quality in geometric distortion, susceptibility artifacts, and lesion conspicuity, and provided highly correlated and consistent mean ADC values when compared to SS-EPI DWI, indicating the feasibility of RS-EPI DWI of testes.

Comparing the clinical utility of single-shot, readout-segmented and zoomit echo-planar imaging in diffusion-weighted imaging of the kidney at 3 T

We compared the clinical utility of single-shot echo-planar imaging (SS-EPI) using different breathing schemes, readout-segmented EPI and zoomit EPI in the repeatability of apparent diffusion coefficient (ADC) measurements, cortico-medullary contrast to noise ratio (c-mCNR) and image quality. In this institutional review board-approved prospective study, some common clinically applicable diffusion-weighted imaging (b = 50, 400, 800 s/mm²) of kidney on 3.0 T MRI were performed on 22 volunteers using SS-EPI with breath-hold diffusion-weighted imaging (BH-DWI), free-breathing (FB-DWI), navigator-triggered (NT-DWI) and respiratory-triggered (RT-DWI), readout-segmented DWI (RS-DWI), and Zoomit DWI (Z-DWI). ADC and c-mCNR were measured in 12 anatomic locations (the upper, middle, and lower pole of the renal cortex and medulla), and image quality was assessed on these DWI sequences. A DWI with the optimal clinical utility was decided by systematically assessing the ADC repeatability, c-mCNR and image quality among the DWIs. For ADC measurements, Z-DWI had an excellent intra-observer agreement (intra-class correlation coefficients (ICCs): 0.876–0.944) and good inter-observer agreement (inter-class ICCs: 0.798–0.856) in six DWI sequences. Z-DWI had the highest ADC repeatability in most of the 12 anatomic locations of the kidneys (mean ADC absolute difference: 0.070–0.111 × 10⁻³ mm²/s, limit of agreement: 0.031–0.056 × 10⁻³ mm²/s). In all DWIs, Z-DWI yielded a slightly higher c-mCNR than other DWIs in most representative locations (P > 0.05), which was significantly higher than BH-DWI and FB-DWI in the middle pole of both kidneys and the upper pole of the left kidney (P < 0.05). In addition, Z-DWI yielded image quality that was similar to RT-DWI and NT-DWI (P > 0.05) and superior to BH-DWI, FB-DWI and RS-DWI (P < 0.05). Our results suggest that Z-DWI provides the highest ADC reproducibility, better c-mCNR and good image quality on 3.0 T MRI, making it the recommended sequence for clinical DWI of the kidney.

Diffusion-weighted magnetic resonance imaging in rat kidney using two-dimensional navigated, interleaved echo-planar imaging at 7.0 T

The purpose of this study was to investigate the feasibility of two-dimensional (2D) navigated, interleaved multishot echo-planar imaging (EPI) to enhance kidney diffusion-weighted imaging (DWI) in rats at 7.0 T. Fully sampled interleaved four-shot EPI with 2D navigators was tailored for kidney DWI (Sprague-Dawley rats, n = 7) on a 7.0-T small bore preclinical scanner. The image quality of four-shot EPI was compared with T₂ -weighted rapid acquisition with relaxation enhancement (RARE) (reference) and single-shot EPI (ss-EPI) without and with parallel imaging (PI). The contrast-to-noise ratio (CNR) was examined to assess the image quality for the EPI approaches. The Dice similarity coefficient and the Hausdorff distance were used for evaluation of image distortion. Mean diffusivity (MD) and fractional anisotropy (FA) were calculated for renal cortex and medulla for all DWI approaches. The corticomedullary difference of MD and FA were assessed by Wilcoxon signed-rank test. Four-shot EPI showed the highest CNR among the three EPI variants and lowest geometric distortion versus T₂ -weighted RARE (mean Dice: 0.77 for ss-EPI without PI, 0.88 for ss-EPI with twofold undersampling, and 0.92 for four-shot EPI). The FA map derived from four-shot EPI clearly identified a highly anisotropic region corresponding to the inner stripe of the outer medulla. Four-shot EPI successfully discerned differences in both MD and FA between renal cortex and medulla. In conclusion, 2D navigated, interleaved multishot EPI facilitates high-quality rat kidney DWI with clearly depicted intralayer and interlayer structure and substantially reduced image distortion. This approach enables the anatomic integrity of DWI-MRI in small rodents and has the potential to benefit the characterization of renal microstructure in preclinical studies.

Diffusion-Magnetic Resonance Imaging predicts decline of kidney function in chronic kidney disease and in patients with a kidney allograft

Kidney cortical interstitial fibrosis is highly predictive of kidney prognosis and is currently assessed by evaluation of a biopsy. Diffusion-weighted magnetic resonance imaging is a promising non-invasive tool to evaluate kidney fibrosis. We recently adapted diffusion-weighted imaging sequence for discrimination between the kidney cortex and medulla and found that the cortico-medullary difference in apparent diffusion coefficient (ΔADC) correlated with histological interstitial fibrosis. Here, we assessed whether ΔADC as measured with diffusion-weighted magnetic resonance imaging is predictive of kidney function decline and dialysis initiation in chronic kidney disease (CKD) and patients with a kidney allograft in a prospective study encompassing 197 patients. We measured ΔADC in 43 patients with CKD (estimated GFR (eGFR) 55ml/min/1.73m²) and 154 patients with a kidney allograft (eGFR 53ml/min/1.73m²). Patients underwent a kidney biopsy and diffusion-weighted magnetic resonance imaging within one week of biopsy; median follow-up of 2.2 years with measured laboratory parameters. The primary outcome was a rapid decline of kidney function (eGFR decline over 30% or dialysis initiation) during follow up. Significantly, patients with a negative ΔADC had 5.4 times more risk of rapid decline of kidney function or dialysis (95% confidence interval: 2.29-12.58). After correction for kidney function at baseline and proteinuria, low ADC still predicted significant kidney function loss with a hazard ratio of 4.62 (95% confidence interval 1.56-13.67) independent of baseline age, sex, eGFR and proteinuria. Thus, low ΔADC can be a predictor of kidney function decline and dialysis initiation in patients with native kidney disease or kidney allograft, independent of baseline kidney function and proteinuria.

Turbo Gradient and Spin Echo PROPELLER-Diffusion Weighted Imaging for Orbital Tumors: A Comparative Study With Readout-Segmented Echo-Planar Imaging

Purpose: To qualitatively and quantitatively compare the image quality and diagnostic performance of turbo gradient and spin echo PROPELLER diffusion-weighted imaging (TGSE-PROPELLER-DWI) vs. readout-segmented echo-planar imaging (rs-EPI) in the evaluation of orbital tumors.

Materials and Methods: A total of 43 patients with suspected orbital tumors were enrolled to perform the two DWIs with comparable spatial resolution on 3T. The overall image qualities, geometric distortions, susceptibility artifacts, and lesion conspicuities were scored by using a four-point scale (1, poor; 4, excellent). Quantitative measurements, including contrast-to-noise ratios (CNRs), apparent diffusion coefficients (ADCs), geometric distortion rates (GDRs), and lesion sizes, were calculated and compared. The two ADCs for differentiating malignant from benign orbital tumors were evaluated. Wilcoxon signed-rank test, Kappa statistic, and receiver operating characteristics (ROC) curves were used.

Results: TGSE-PROPELLER-DWI performed superior in all subjective scores and quantitative GDR evaluation than rs-EPI (p < 0.001), and excellent interobserver agreement was obtained for Kappa value ranging from 0.876 to 1.000. ADC_lesion of TGSE-PROPELLER-DWI was significantly higher than those of rs-EPI (p < 0.001). Mean ADC of malignant tumors was significantly lower than that of benign tumors both in two DWIs. However, the AUC for differentiating malignant and benign tumors showed no significant difference in the two DWIs (0.860 vs. 0.854, p = 0.7448). Sensitivity and specificity could achieve 92.86% and 72.73% for TGSE-PROPELLER-DWI with a cutoff value of 1.23 × 10^–3 mm²/s, and 85.71% and 81.82% for rs-EPI with a cutoff value of 0.99 × 10^–3 mm²/s.

Conclusion: Compared with rs-EPI, TGSE-PROPELLER-DWI showed minimized geometric distortion and susceptibility artifacts significantly improved the image quality for orbital tumors and achieved comparable diagnostic performance in differentiating malignant and benign orbital tumors.

Clinical comparison of single-shot EPI, readout-segmented EPI and TGSE-BLADE for diffusion-weighted imaging of cerebellopontine angle tumors on 3 tesla

OBJECTIVE

The complex anatomical structures of cerebellopontine angle (CPA) pose a unique challenge to diffusion weighted imaging (DWI). This study aimed to compare the clinical utility of the prototypic 2D turbo gradient- and spin echo-BLADE-DWI (TGSE-BLADE-DWI) with that of readout-segmented echo-planar DWI (RESOLVE-DWI) and single-shot echo-planar DWI (SS-EPI-DWI) to visualize CPA anatomic structures and identify CPA tumors.

METHODS

A total of 8 volunteers and 36 patients with pathological CPA tumors were enrolled to perform the three DWI sequences at 3 T. Scan time of TGSE-BLADE-DWI, RESOLVE-DWI and SS-EPI-DWI was 5 min 51 s, 5 min 15 s and 1 min 22 s, respectively. Subjective analysis, including visualization of anatomical structures, geometric distortion, ghosting artifacts, lesion conspicuity, diagnostic confidence, and overall image quality of the three DWI sequences were scored and assessed. Signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR) and apparent diffusion coefficient (ADC) of CPA tumors were measured and compared.

RESULTS

A total of 39 lesions were identified, TGSE-BLADE-DWI detected all of them, RESOLVE-DWI 36 and SS-EPI-DWI 27. Significant differences were found in all the subjective parameters among the three DWI sequences (all p < 0.001). TGSE-BLADE-DWI was significantly better than RESOLVE-DWI in visualization of CPA anatomical structures, geometric distortion, ghosting artifacts, lesion conspicuity, diagnostic confidence, and overall image quality (all p < 0.01), and RESOLVE-DWI showed significantly superior performance than SS-EPI-DWI in all parameters (all p < 0.001). CNRs and ADCs were not significantly different among the three DWI sequences (p = 0.355, p = 0.590, respectively). No significant differences were detected between TGSE-BLADE-DWI SNR and RESOLVE-DWI SNR (p = 0.058), or TGSE-BLADE-DWI SNR and SS-EPI-DWI SNR (p = 0.155).

CONCLUSION

Compared with RESOLVE-DWI and SS-EPI-DWI, TGSE-BLADE-DWI minimized geometric distortions and ghosting artifacts and demonstrated an improved ability for depicting CPA tumors with better lesion conspicuity.

SUMMARY

Geometric distortions and ghosting artifacts are found at bone-air interfaces using conventional diffusion-weighted imaging (DWI), which is a challenge for imaging cerebellopontine angle (CPA) tumors. Our study validated that geometric distortions and ghosting artifacts were not present on 2D turbo gradient- and spin-echo-BLADE-DWI scans, making this technique useful for visualizing CPA anatomic structures and diagnosing CPA tumors.

Imaging of renal fibrosis

PURPOSE OF REVIEW

Fibrosis is an important biomarker of chronic kidney injury, and a powerful predictor of renal outcome. Currently, the only method for measuring fibrotic burden is histologic analysis, which requires a kidney biopsy in humans, or kidney removal in animal models. These requirements have not only hindered our ability to manage patients effectively, but have also prevented a full understanding of renal fibrosis pathogenesis, and slowed the translation of new antifibrotic agents. The development of noninvasive fibrosis imaging tools could thus transform both clinical care and renal fibrosis research.

RECENT FINDINGS

Conventional imaging modalities have historically failed to image fibrosis successfully. However, recent exciting technological advances have greatly enhanced their capabilities. New techniques, for example, may allow imaging of the physical consequences of scarring, as surrogate measures of renal fibrosis. Similarly, other groups have developed ways to directly image extracellular matrix, either with the use of contrast-enhanced probes, or using matrix components as endogenous contrast agents.

SUMMARY

New developments in imaging technology have the potential to transform our ability to visualize renal fibrosis and to monitor its progression. In doing so, these advances could have major implications for kidney disease care, the development of new antiscarring agents, and our understanding of renal fibrosis in general.

Identifying lumbosacral plexus nerve root abnormalities in patients with sciatica using 3T readout-segmented echo-planar diffusion weighted MR neurography

Objectives

To investigate the accuracy of Diffusion Weighted Imaging (DWI) using the Readout Segmentation of Long Variable Echo-trains (RESOLVE) sequence in detecting lumbosacral nerve abnormalities.

Methods

Following institutional ethics committee approval, patients with sciatica-type lower limb radicular symptoms (n = 110) were recruited and prospectively scanned using 3T MRI. Additional participants (n = 17) who underwent neurophysiological testing (EMG/NCV), were also prospectively studied. In addition to routine lumbar spine MRI, a DWI-RESOLVE sequence of the lumbosacral plexus was performed. Two radiologists, blinded to the side of patient symptoms, independently evaluated the MR images. The size and signal intensity changes of the nerves were evaluated using ordinal 4-point Likert-scales. Signal-to-noise ratio (SNR), apparent diffusion coefficient (ADC) and size were measured for affected and normal nerves. Inter-observer agreement was determined with kappa statistics; κ.

Results

In patients who did not undergo EMG/NCV testing (n = 110), the DWI-RESOLVE sequence detected lumbosacral nerve abnormalities that correlated with symptoms in 36.3% (40/110). This is a similar percentage to patients who underwent EMG/NCV testing, which was positive and correlated with symptoms in 41.2% (7/17). Inter-observer agreement for evaluation of lumbosacral nerve abnormalities was excellent and ranged from 0.87 to 0.94. SNR and nerve size measurements demonstrated statistically significant differences for the L5 and S1 nerves (p value < 0.05) for patients who did not undergo EMG/NCV testing.

Conclusion

The DWI-RESOLVE sequence is a promising new method that may permit accurate detection and localization of lumbar nerve abnormalities in patients with sciatica.

Renal Diffusion-Weighted Imaging (DWI) for Apparent Diffusion Coefficient (ADC), Intravoxel Incoherent Motion (IVIM), and Diffusion Tensor Imaging (DTI): Basic Concepts

The specialized function of the kidney is reflected in its unique structure, characterized by juxtaposition of disorganized and ordered elements, including renal glomerula, capillaries, and tubules. The key role of the kidney in blood filtration, and changes in filtration rate and blood flow associated with pathological conditions, make it possible to investigate kidney function using the motion of water molecules in renal tissue. Diffusion-weighted imaging (DWI) is a versatile modality that sensitizes observable signal to water motion, and can inform on the complexity of the tissue microstructure. Several DWI acquisition strategies are available, as are different analysis strategies, and models that attempt to capture not only simple diffusion effects, but also perfusion, compartmentalization, and anisotropy. This chapter introduces the basic concepts of DWI alongside common acquisition schemes and models, and gives an overview of specific DWI applications for animal models of renal disease.This chapter is based upon work from the COST Action PARENCHIMA, a community-driven network funded by the European Cooperation in Science and Technology (COST) program of the European Union, which aims to improve the reproducibility and standardization of renal MRI biomarkers. This introduction chapter is complemented by two separate chapters describing the experimental procedure and data analysis.

Renal fibrosis detected by diffusion-weighted magnetic resonance imaging remains unchanged despite treatment in subjects with renovascular disease

Tissue fibrosis is an important index of renal disease progression. Diffusion-weighted magnetic resonance imaging’s (DWI-MRI) apparent diffusion coefficient (ADC) reveals water diffusion is unobstructed by microstructural alterations like fibrosis. We hypothesized that ADC may indicate renal injury and response to therapy in patients with renovascular disease (RVD). RVD patients were treated with medical therapy (MT) and percutaneous transluminal renal angioplasty (MT + PTRA) (n = 11, 3 bilaterally, n = 14 kidneys) or MT (n = 9). ADC and renal hypoxia (R2*) by blood-oxygen-level-dependent MRI were studied before (n = 27) and 3 months after (n = 20) treatment. Twelve patients underwent renal biopsies. Baseline ADC values were correlated with changes in eGFR, serum creatinine (SCr), systolic blood pressure (SBP), renal hypoxia, and renal vein levels of pro-inflammatory marker tumor necrosis-factor (TNF)-α. Renal oxygenation, eGFR, and SCr improved after MT + PTRA. ADC inversely correlated with the histological degree of renal fibrosis, but remained unchanged after MT or MT + PTRA. Basal ADC values correlated modestly with change in SBP, but not in renal hypoxia, TNF-α levels, or renal function. Lower ADC potentially reflects renal injury in RVD patients, but does not change in response to medical or interventional therapy over 3 months. Future studies need to pinpoint indices of kidney recovery potential.

Analysis of Apparent Diffusion Coefficients of the Brain in Healthy Controls: A Comparison Study between Single-Shot Echo-Planar Imaging and Read-out-Segmented Echo-Planar Imaging

OBJECTIVE

To compare apparent diffusion coefficients (ADCs) of brain segments by using two diffusion-weighted imaging acquisition modes, single-shot echo-planar imaging (ss-EPI) and read-out-segmented echo-planar imaging (rs-EPI), and to assess their correlation and agreement in healthy controls.

MATERIALS AND METHODS

T2-weighted (T2W) images, rs-EPI, and ss-EPI of 30 healthy subjects were acquired using a 3T magnetic resonance scanner. The T2W images were co-registered to the rs-EPI and ss-EPI, which were then segmented into the gray matter (GM), white matter (WM), and cerebrospinal fluid (CSF) to generate masking templates. ADC maps of rs-EPI and ss-EPI were also segmented into the GM, WM, and CSF by using the generated templates. ADCs of rs-EPI and ss-EPI were compared using Student's t tests and correlated using Pearson's correlation coefficients. Bland-Altman plots were used to assess the agreement between acquisitions.

RESULTS

ADCs of rs-EPI and ss-EPI were significantly different in the GM (p < 0.001) and WM (p < 0.001). ADCs showed high agreement and correlation in the whole brain and CSF (r > 0.988; p < 0.001). ADC of the WM showed the least correlation (r = 0.894; p < 0.001), and ADCs of the WM and GM showed poor agreement. Pearson's correlation equations for each brain segment were y = 1.1x - 59.4 (GM), y = 1.45x - 255 (WM), and y = 0.98x - 63.5 (CSF), where x and y indicated ADCs of rs-EPI and ss-EPI, respectively.

CONCLUSION

While ADCs of rs-EPI and ss-EPI showed high correlation and agreement in the whole brain and CSF, ADCs of the WM and GM showed significant differences and large variability, reflecting brain parenchymal inhomogeneity due to different regional microenvironments. ADCs of different acquisition methods should be interpreted carefully, especially in intra-individual comparisons.

Diffusion-weighted Renal MRI at 9.4 Tesla Using RARE to Improve Anatomical Integrity

Diffusion-weighted magnetic resonance imaging (DWI) is a non-invasive imaging technique sensitive to tissue water movement. By enabling a discrimination between tissue properties without the need of contrast agent administration, DWI is invaluable for probing tissue microstructure in kidney diseases. DWI studies commonly make use of single-shot Echo-Planar Imaging (ss-EPI) techniques that are prone to suffering from geometric distortion. The goal of the present study was to develop a robust DWI technique tailored for preclinical magnetic resonance imaging (MRI) studies that is free of distortion and sensitive to detect microstructural changes. Since fast spin-echo imaging techniques are less susceptible to B₀ inhomogeneity related image distortions, we introduced a diffusion sensitization to a split-echo Rapid Acquisition with Relaxation Enhancement (RARE) technique for high field preclinical DWI at 9.4 T. Validation studies in standard liquids provided diffusion coefficients consistent with reported values from the literature. Split-echo RARE outperformed conventional ss-EPI, with ss-EPI showing a 3.5-times larger border displacement (2.60 vs. 0.75) and a 60% higher intra-subject variability (cortex = 74%, outer medulla = 62% and inner medulla = 44%). The anatomical integrity provided by the split-echo RARE DWI technique is an essential component of parametric imaging on the way towards robust renal tissue characterization, especially during kidney disease.

A new method for detecting the outer corneal contour in images from an ultra-fast Scheimpflug camera

Background

The Corvis^® ST tonometer is an innovative device which, by combining a classic non-contact tonometer with an ultra-fast Scheimpflug camera, provides a number of parameters allowing for the assessment of corneal biomechanics. The acquired biomechanical parameters improve medical diagnosis of selected eye diseases. One of the key elements in biomechanical measurements is the correct corneal contour detection, which is the basis for further calculations. The presented study deals with the problem of outer corneal edge detection based on a series of images from the afore-mentioned device. Corneal contour detection is the first and extremely important stage in the acquisition and analysis of corneal dynamic parameters.

Result

A total of 15,400 images from the Corvis^® ST tonometer acquired from 110 patients undergoing routine ophthalmologic examinations were analysed. A method of outer corneal edge detection on the basis of a series of images from the Corvis^® ST was proposed. The method was compared with known and commonly used edge detectors: Sobel, Roberts, and Canny operators, as well as others, known from the literature. The analysis was carried out in MATLAB^® version 9.0.0.341360 (R2016a) with the Image Processing Toolbox (version 9.4) and the Neural Network Toolbox (version 9.0). The method presented in this paper provided the smallest values of the mean error (0.16%), stability (standard deviation 0.19%) and resistance to noise, characteristic for Corvis^® ST tonometry tests, compared to the methods known from the literature. The errors were 5.78 ± 9.19%, 3.43 ± 6.21%, and 1.26 ± 3.11% for the Roberts, Sobel, and Canny methods, respectively.

Conclusions

The proposed new method for detecting the outer corneal contour increases the accuracy of intraocular pressure measurements. It can be used to analyse dynamic parameters of the cornea.

Consensus-based technical recommendations for clinical translation of renal diffusion-weighted MRI

Objectives

Standardization is an important milestone in the validation of DWI-based parameters as imaging biomarkers for renal disease. Here, we propose technical recommendations on three variants of renal DWI, monoexponential DWI, IVIM and DTI, as well as associated MRI biomarkers (ADC, D, D*, f, FA and MD) to aid ongoing international efforts on methodological harmonization.

Materials and methods

Reported DWI biomarkers from 194 prior renal DWI studies were extracted and Pearson correlations between diffusion biomarkers and protocol parameters were computed. Based on the literature review, surveys were designed for the consensus building. Survey data were collected via Delphi consensus process on renal DWI preparation, acquisition, analysis, and reporting. Consensus was defined as ≥ 75% agreement.

Results

Correlations were observed between reported diffusion biomarkers and protocol parameters. Out of 87 survey questions, 57 achieved consensus resolution, while many of the remaining questions were resolved by preference (65–74% agreement). Summary of the literature and survey data as well as recommendations for the preparation, acquisition, processing and reporting of renal DWI were provided.

Discussion

The consensus-based technical recommendations for renal DWI aim to facilitate inter-site harmonization and increase clinical impact of the technique on a larger scale by setting a framework for acquisition protocols for future renal DWI studies. We anticipate an iterative process with continuous updating of the recommendations according to progress in the field.

Electronic supplementary material

The online version of this article (10.1007/s10334-019-00790-y) contains supplementary material, which is available to authorized users.

Noninvasive assessment of renal fibrosis by magnetic resonance imaging and ultrasound techniques

Renal fibrosis is a useful biomarker for diagnosis and guidance of therapeutic interventions of chronic kidney disease (CKD), a worldwide disease that affects more than 10% of the population and is one of the major causes of death. Currently, tissue biopsy is the gold standard for assessment of renal fibrosis. However, it is invasive, and prone to sampling error and observer variability, and may also result in complications. Recent advances in diagnostic imaging techniques, including magnetic resonance imaging (MRI) and ultrasonography, have shown promise for noninvasive assessment of renal fibrosis. These imaging techniques measure renal fibrosis by evaluating its impacts on the functional, mechanical, and molecular properties of the kidney, such as water mobility by diffusion MRI, tissue hypoxia by blood oxygenation level dependent MRI, renal stiffness by MR and ultrasound elastography, and macromolecule content by magnetization transfer imaging. Other MR techniques, such as T₁/T₂ mapping and susceptibility-weighted imaging have also been explored for measuring renal fibrosis. Promising findings have been reported in both preclinical and clinical studies using these techniques. Nevertheless, limited specificity, sensitivity, and practicality in these techniques may hinder their immediate application in clinical routine. In this review, we will introduce methodologies of these techniques, outline their applications in fibrosis imaging, and discuss their limitations and pitfalls.

Value of High-Resolution DWI in Combination With Texture Analysis for the Evaluation of Tumor Response After Preoperative Chemoradiotherapy for Locally Advanced Rectal Cancer

OBJECTIVE. The purpose of this study is to determine the performance of the apparent diffusion coefficient (ADC) value calculated from high-resolution DWI using readout-segmented echo-planar imaging (rs-EPI) and to assess the texture parameters of T2-weighted MR images in identifying pathologic complete response (pCR) after patients with locally advanced rectal cancer (LARC) undergo preoperative chemoradiotherapy (CRT). MATERIALS AND METHODS. A total of 76 patients with LARC who underwent preoperative CRT and subsequent surgery were enrolled in the study retrospectively. All patients underwent post-CRT MRI, which included acquisition of a DWI sequence with use of the rs-EPI technique. The histopathologic tumor regression grade was the reference standard. Patients were subdivided into pCR and non-pCR groups. Two radiologists independently drew whole-tumor ROIs on DW images and T2-weighted MR images to calculate the mean ADC value and first-order texture parameters. RESULTS. Interobserver agreement was good to excellent (intraclass correlation coefficient [ICC], 0.79-0.993) for imaging analysis. Calculated from high-resolution DWI, the mean post-CRT ADC value was significantly higher in the pCR group (p < 0.001). The pCR group also showed lower uniformity (p < 0.001) of the T2-weighted image. The mean ADC value and uniformity were significantly correlated with the tumor regression grade. The mean ADC value was a good indicator for differentiating pCR from absence of pCR (ROC AUC value, 0.912). Uniformity (ROC AUC value, 0.776) showed a moderate ability to identify pCR. Combining the mean ADC value and uniformity yielded an ROC AUC value comparable to that of the mean ADC value (p = 0.125). CONCLUSION. Mean post-CRT ADC values calculated from high-resolution DWI using rs-EPI could effectively select for patients with LARC who have a pCR after preoperative CRT. First-order texture parameters of T2-weighted MR images could also identify patients with pCR by reflecting tumor heterogeneity, even though they could not significantly improve the diagnostic performance.

Validation of the corticomedullary difference in magnetic resonance imaging-derived apparent diffusion coefficient for kidney fibrosis detection: a cross-sectional study

Background

Kidney cortical interstitial fibrosis (IF) is highly predictive of renal prognosis and is currently assessed by the evaluation of a biopsy. Diffusion magnetic resonance imaging (MRI) is a promising tool to evaluate kidney fibrosis via the apparent diffusion coefficient (ADC), but suffers from inter-individual variability. We recently applied a novel MRI protocol to allow calculation of the corticomedullary ADC difference (ΔADC). We here present the validation of ΔADC for fibrosis assessment in a cohort of 164 patients undergoing biopsy and compare it with estimated glomerular filtration rate (eGFR) and other plasmatic parameters for the detection of fibrosis.

Methods

This monocentric cross-sectional study included 164 patients undergoing renal biopsy at the Nephrology Department of the University Hospital of Geneva between October 2014 and May 2018. Patients underwent diffusion-weighted imaging, and T1 and T2 mappings, within 1 week after biopsy. MRI results were compared with gold standard histology for fibrosis assessment.

Results

Absolute cortical ADC or cortical T1 values correlated poorly to IF assessed by the biopsy, whereas ΔADC was highly correlated to IF (r=−0.52, P &lt; 0.001) and eGFR (r = 0.37, P &lt; 0.01), in both native and allograft patients. ΔT1 displayed a lower, but significant, correlation to IF and eGFR, whereas T2 did not correlate to IF nor to eGFR. ΔADC, ΔT1 and eGFR were independently associated with kidney fibrosis, and their combination allowed detection of extensive fibrosis with good specificity.

Conclusion

ΔADC is better correlated to IF than absolute cortical or medullary ADC values. ΔADC, ΔT1 and eGFR are independently associated to IF and allow the identification of patients with extensive IF.

Comparison between readout-segmented and single-shot echo-planar imaging in the evaluation of cervical cancer staging

OBJECTIVE:

To compare the performance of diffusion-weighted imaging (DWI) based on readout-segmented echo-planar imaging (RESOLVE) and single-shot EPI (SS-EPI) sequence in evaluating cervical cancer staging.

METHODS:

61 patients with cervical cancer underwent DWI based on SS-EPI and RESOLVE. Two blinded readers independently assessed two sets of DW images for distinction of anatomical structures, delineation of lesion, susceptibility artefact and overall image quality on a 4-point scale. Geometric distortion was evaluated by measuring lesion anteroposterior (AP) length and left-right (LR) width derived from T₂W images and those obtained from the corresponding DW images. Staging of cervical cancer on SS-EPI and RESOLVE were compared with T₂WI and gold-standard of pathological findings.

RESULTS:

RESOLVE was significantly superior to SS-EPI for all four criteria regarding qualitative comparisons (all p < 0.05). Regarding the geometric distortion, AP length on SS-EPI was significantly different from that of T₂WI (p < 0.05), whereas there were no significant differences between RESOLVE and T₂WI (both p > 0.05). The staging of SS-EPI was overestimated, while RESOLVE had a better consistency with pathological staging than SS-EPI in staging of cervical cancer. There was no significant difference in apparent diffusion coefficient value between SS-EPI and RESOLVE (p < 0.05).

CONCLUSION:

RESOLVE is superior to SS-EPI in the accuracy of cervical cancer staging because of the improvement in image quality.

ADVANCES IN KNOWLEDGE:

RESOLVE has a more accurate value comparable to SS-EPI in cervical cancer staging, with the advantage of the improvement in image quality and reduced geometric distortion.

In Vivo Imaging Markers for Prediction of Radiotherapy Response in Patients with Nasopharyngeal Carcinoma: RESOLVE DWI versus DKI

In this prospective study, we compared the performance of readout segmentation of long variable echo trains of diffusion-weighted imaging (RESOLVE DWI) and diffusion kurtosis imaging (DKI) for the prediction of radiotherapy response in patients with nasopharyngeal carcinoma (NPC). Forty-one patients with NPC were evaluated. All patients underwent conventional MRI, RESOLVE DWI and DKI, before and after radiotherapy. All patients underwent conventional MRI every 3 months until 1 year after radiotherapy. The patients were divided into response group (RG; 36/41 patients) and no-response group (NRG; 5/41 patients) based on follow-up results. DKI (the mean of kurtosis coefficient, Kmean and the mean of diffusion coefficient, Dmean) and RESOLVE DWI (the minimum apparent diffusion coefficient, ADC_min) parameters were calculated. Parameter values at the pre-treatment period, post-treatment period, and the percentage change between these 2 periods were obtained. All parameters differed between the RG and NRG groups except for the pretreatment Dmean and ADC_min. Kmean-post was considered as an independent predictor of local control, with 87.5% sensitivity and 91.3% specificity (optimal threshold = 0.30, AUC: 0.924; 95% CI, 0.83-1.00). Kmean-post values of DKI have the potential to be used as imaging biomarkers for the early evaluation of treatment effects of radiotherapy on NPC.

Diffusion-weighted magnetic resonance imaging to assess diffuse renal pathology: a systematic review and statement paper

Diffusion-weighted magnetic resonance imaging (DWI) is a non-invasive method sensitive to local water motion in the tissue. As a tool to probe the microstructure, including the presence and potentially the degree of renal fibrosis, DWI has the potential to become an effective imaging biomarker. The aim of this review is to discuss the current status of renal DWI in diffuse renal diseases. DWI biomarkers can be classified in the following three main categories: (i) the apparent diffusion coefficient-an overall measure of water diffusion and microcirculation in the tissue; (ii) true diffusion, pseudodiffusion and flowing fraction-providing separate information on diffusion and perfusion or tubular flow; and (iii) fractional anisotropy-measuring the microstructural orientation. An overview of human studies applying renal DWI in diffuse pathologies is given, demonstrating not only the feasibility and intra-study reproducibility of DWI but also highlighting the need for standardization of methods, additional validation and qualification. The current and future role of renal DWI in clinical practice is reviewed, emphasizing its potential as a surrogate and monitoring biomarker for interstitial fibrosis in chronic kidney disease, as well as a surrogate biomarker for the inflammation in acute kidney diseases that may impact patient selection for renal biopsy in acute graft rejection. As part of the international COST (European Cooperation in Science and Technology) action PARENCHIMA (Magnetic Resonance Imaging Biomarkers for Chronic Kidney Disease), aimed at eliminating the barriers to the clinical use of functional renal magnetic resonance imaging, this article provides practical recommendations for future design of clinical studies and the use of renal DWI in clinical practice.

The impact of computed high b-value images on the diagnostic accuracy of DWI for prostate cancer: A receiver operating characteristics analysis

To evaluate the performance of computed high b value diffusion-weighted images (DWI) in prostate cancer detection. 97 consecutive patients who had undergone multiparametric MRI of the prostate followed by biopsy were reviewed. Five radiologists independently scored 138 lesions on native high b-value images (b = 1200 s/mm²), apparent diffusion coefficient (ADC) maps, and computed high b-value images (contrast equivalent to b = 2000 s/mm²) to compare their diagnostic accuracy. Receiver operating characteristic (ROC) analysis and McNemar’s test were performed to assess the relative performance of computed high b value DWI, native high b-value DWI and ADC maps. No significant difference existed in the area under the curve (AUC) for ROCs comparing B1200 (b = 1200 s/mm²) to computed B2000 (c-B2000) in 5 readers. In 4 of 5 readers c-B2000 had significantly increased sensitivity and/or decreased specificity compared to B1200 (McNemar’s p < 0.05), at selected thresholds of interpretation. ADC maps were less accurate than B1200 or c-B2000 for 2 of 5 readers (P < 0.05). This study detected no consistent improvement in overall diagnostic accuracy using c-B2000, compared with B1200 images. Readers detected more cancer with c-B2000 images (increased sensitivity) but also more false positive findings (decreased specificity).

Bladder cancer: detection and image quality compared among iShim, RESOLVE, and ss-EPI diffusion-weighted MR imaging with high b value at 3.0 T MRI

To compare the detection of bladder neoplasms and image quality among the diffusion-weighted imaging (DWI) acquired by the prototype single-shot echo-planar-imaging (ss-EPI) sequence for integrated slice-specific dynamic shimming (iShim), readout segmentation of long variable echo trains (RESOLVE) and conventional ss-EPI sequences.Around 63 patients with 77 bladder lesions were enrolled. The MR protocol included T1WI, T2WI and 3 types of DWI. The sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and accuracy of each DWI for the detection of bladder tumor were computed. The subjective scores of imaging quality, diagnostic confidence, and detection of tumors of stage T2 or greater were recorded. The contrast-to-noise ratio (CNR), signal intensity ratios, and apparent diffusion coefficient (ADC) values were measured. The univariate analysis of variance technique, the Friedman test, and Bland-Altman plots were used in the statistical analysis. Observer performance of tumor T stage was tested using receiver operating characteristic (ROC) curve analysis.The sensitivity, NPV, and accuracy of iShim (92.75%; 61.54%; 93.51%) for detection of bladder tumor were superior to those of RESOLVE (84.06%; 42.11%; 85.71%) and ss-EPI (86.96%; 47.06%; 88.31%). All qualitative scores of iShim were higher than RESOLVE (all P < .05) and ss-EPI (all P < .05). The CNR, signal intensity ratios between bladder lesion and urine, lesion, and submucosal stalk (or nearby normal bladder wall), and between distal normal bladder wall and urine of iShim (39.84 ± 12.11, 2.40 ± 0.60, 1.98 ± 0.43, 1.28 ± 0.16) were higher than RESOLVE (16.97 ± 7.08, 1.62 ± 0.41, 1.52 ± 0.42, 1.15 ± 0.29, all P < .05) and ss-EPI (27.89 ± 9.65, 1.66 ± 0.46, 1.57 ± 0.50, 0.99 ± 0.22, all P < .05). No significant difference of ADC values were found for iShim and RESOLVE (P=0.46), iShim, and ss-EPI (P = 0.97), RESOLVE and ss-EPI (P = .48). The Az value for the detection of tumors of stage T2 or greater was slightly higher with the iShim DWI sequence (0.89) than with the RESOLVE (0.87, P = 0.72) or ss-EPI (0.85, P = .38) sequence.The iShim DWI has relatively better detection of bladder tumor and image quality without significant ADC value difference.

Readout-segmented echo-planar diffusion-weighted imaging in the assessment of orbital tumors: comparison with conventional single-shot echo-planar imaging in image quality and diagnostic performance

Background Readout-segmented echo-planar imaging (RS-EPI) could improve the imaging quality of diffusion-weighted imaging (DWI) in various organs. However, whether it could improve the imaging quality and diagnostic performance for the patients with orbital tumors is still unknown. Purpose To compare the image quality and diagnostic performance of RS-EPI DWI with that of conventional single-shot EPI (SS-EPI) DWI in patients with orbital tumors. Material and Methods SS-EPI and RS-EPI DW images of 32 patients with pathologically diagnosed orbital tumors were retrospectively analyzed. Qualitative imaging parameters (imaging sharpness, geometric distortion, ghosting artifacts, and overall imaging quality) and quantitative imaging parameters (apparent diffusion coefficient [ADC], signal-to-noise ratio [SNR], contrast, and contrast-to-noise ratio [CNR]) were assessed by two independent radiologists, and compared between SS-EPI and RS-EPI DWI. Receiver operating characteristic curves were used to determine the diagnostic value of ADC in differentiating malignant from benign orbital tumors. Results RS-EPI DW imaging produced less geometric distortion and ghosting artifacts, and better imaging sharpness and overall imaging quality than SS-EPI DWI (for all, P < 0.001). Meanwhile, RS-EPI DWI produced significantly lower SNR ( P < 0.001) and ADC ( P < 0.001), and higher contrast ( P < 0.001) than SS-EPI DWI, while producing no difference in CNR ( P = 0.137). There was no significant difference on the diagnostic performance between SS-EPI and RS-EPI DWI, when using ADC as the differentiating index ( P = 0.529). Conclusion Compared with SS-EPI, RS-EPI DWI provided significantly better imaging quality and comparable diagnostic performance in differentiating malignant from benign orbital tumors.

Simultaneous Multislice Diffusion-Weighted Imaging of the Kidney: A Systematic Analysis of Image Quality

OBJECTIVES

The aims of this study were to implement a protocol for simultaneous multislice (SMS) accelerated diffusion-weighted imaging (DWI) of the kidneys and to perform a systematic analysis of image quality of the data sets.

MATERIALS AND METHODS

Ten healthy subjects and 5 patients with renal masses underwent DWI of the kidney in this prospective institutional review board-approved study on a 3 T magnetic resonance scanner. Simultaneous multislice DWI echo-planar sequences (acceleration factors [AFs] 2 and 3) were compared with conventional echo-planar DWI as reference standard for each acquisition scheme. The following 3 acquisition schemes were applied: comparison A, with increased number of acquisitions at constant scan time; comparison B, with reduction of acquisition time; and comparison C, with increased slice resolution (constant acquisition time, increasing number of slices). Interreader reliability was analyzed by calculating the intraclass correlation coefficient (ICC). Qualitative image quality features were evaluated by 2 independent radiologists on a 5-point Likert scale. Quantification accuracy of the apparent diffusion coefficients (ADCs) and signal-to-noise ratios (SNRs) were assessed by region of interest analysis. Furthermore, lesion conspicuity in the 5 patients was assessed using a 5-point Likert scale by 2 independent radiologists.

RESULTS

Interreader agreement was substantial with an ICC of 0.68 for the overall image quality and an ICC of 0.73 for the analysis of artifacts. In comparison A, AF2 resulted in increased SNR (P < 0.05) by 21% at stable image quality scores (image quality: P = 0.76, artifacts: P = 0.21). In comparison B, applying AF2, the scan time could be reduced by 46% without significant reduction in qualitative image quality scores (P = 0.059) or SNR (P = 0.126). In comparison C, slice resolution could be improved by 28% using AF2 with stable image quality scores and SNR. In general, AF3 resulted in reduced image quality and SNR. Significantly reduced ADC values were observed for AF3 in comparison C (cortex: P = 0.003; medulla: P = 0.001) compared with the standard echo-planar imaging sequence. The conventional DWI and the SMS DWI with AF2 showed stable lesion conspicuity ([AF1/AF2]: reader 1 [1.8/1.4] and reader 2 [1.8/1.4]). The lesion conspicuity was lower using AF3 (reader 1: 2.2 and reader 2: 1.8).

CONCLUSIONS

In conclusion, SMS DWI of the kidney is a potential tool to substantially reduce scan time without negative effects on SNR, ADC quantification accuracy, and image quality if an AF2 is used. Although AF3 results in even higher scan time reduction, a negative impact on image quality, SNR, ADC quantification accuracy, and lesion conspicuity must be considered.

Image formation in diffusion MRI: A review of recent technical developments

Diffusion magnetic resonance imaging (MRI) is a standard imaging tool in clinical neurology, and is becoming increasingly important for neuroscience studies due to its ability to depict complex neuroanatomy (eg, white matter connectivity). Single-shot echo-planar imaging is currently the predominant formation method for diffusion MRI, but suffers from blurring, distortion, and low spatial resolution. A number of methods have been proposed to address these limitations and improve diffusion MRI acquisition. Here, the recent technical developments for image formation in diffusion MRI are reviewed. We discuss three areas of advance in diffusion MRI: improving image fidelity, accelerating acquisition, and increasing the signal-to-noise ratio.

LEVEL OF EVIDENCE

5 Technical Efficacy: Stage 1 J. MAGN. RESON. IMAGING 2017;46:646-662.

Recent Advances in Magnetic Resonance Imaging Assessment of Renal Fibrosis

CKD is a global public health problem. Renal fibrosis is a final common pathway leading to progressive loss of function in CKD. The degree of renal fibrosis predicts the prognosis of CKD. Recent studies have shown that bone marrow-derived fibroblasts contribute significantly to the development of renal fibrosis, which may yield novel therapeutic strategy for fibrotic kidney disease. Therefore, it is imperative to accurately assess the degree of renal fibrosis noninvasively to identify those patients who can benefit from antifibrotic therapy. In this review, we summarize recent advances in the assessment of renal fibrosis by magnetic resonance imaging.

Diffusion tensor imaging of the renal cortex in diabetic patients: correlation with urinary and serum biomarkers

PURPOSE

To demonstrate role of diffusion tensor imaging of the kidney in diabetic patients and to correlate renal fractional anisotropy (FA) and apparent diffusion coefficient (ADC) of the renal cortex with urinary and serum biomarkers of diabetes.

MATERIAL AND METHODS

Prospective study was conducted upon 42 diabetic patients (28 males, 14 females; mean age = 33 years) and 17 age- and sex-matched volunteers. Diabetic patients were micro-normoalbuminuric (n = 27) and macroalbuminuric (n = 15). Patients and volunteers underwent diffusion tensor imaging of the kidney. The FA and ADC of the renal cortex were calculated from 3 regions of interests of both kidneys.

RESULTS

The mean FA and ADC of the renal cortex in diabetic patients (0.36 ± 0.10 and 1.74 ± 0.16 × 10^-3 mm²/s) was significantly different (p = 0.001) from that of volunteers (0.26 ± 0.02 and 1.88 ± 0.03 × 10^-3 mm²/s). The cut-off renal FA and ADC used to differentiate diabetic patients from volunteers were 0.28 and 1.89 × 10^-3 mm²/s with AUC of 0.791 and 0.773 and accuracy of 71% and 76%. The FA and ADC calculated in the renal cortex in patients with macroalbuminuria (0.43 ± 0.10 and 1.63 ± 0.19 × 10^-3 mm²/s) was significantly different (p = 0.001) from that of patients with micro-normoalbuminuria (0.35 ± 0.12 and 1.80 ± 0.18 × 10^-3 mm²/s). The FA and ADC of the renal cortex in diabetic patients correlated with urinary albumin (r = 0.530; p = 0.001, r = -0.421; p = 0.006), urinary NAG (r = 0.376; p = 0.014, r = -0.245; p = 0.01), urinary TGF-β1 (r = 0.287; p = 0.065, r = -0.214; p = 0.175), and serum creatinine (r = 0.381; p = 0.013, r = -0.349; p = 0.023).

CONCLUSION

The FA and ADC of the renal cortex may help in differentiation of diabetic kidney from volunteers and prediction of the presence of macroalbuminuria in diabetic patients and correlated with some of the urinary and serum biomarkers of diabetes.

Dynamic Volume Assessment of Hepatocellular Carcinoma in Rat Livers Using a Clinical 3T MRI and Novel Segmentation

PURPOSE

In vivo liver cancer research commonly uses rodent models. One of the limitations of such models is the lack of accurate and reproducible endpoints for a dynamic assessment of growing tumor nodules. The aim of this study was to validate a noninvasive, true volume segmentation method using two rat hepatocellular carcinoma (HCC) models, correlating magnetic resonance imaging (MRI) with histological volume measurement, and with blood levels of α-fetoprotein.

MATERIALS AND METHODS

We used 3T clinical MRI to quantify tumor volume with follow-up over time. Using two distinct rat HCC models, calculated MRI tumor volumes were correlated with volumes from histological sections, or with blood levels of α-fetoprotein. Eleven rats, comprising six Buffalo rats (n = 9 scans) and five Fischer rats (n = 14 tumors), were injected in the portal vein with 2.5 × 10⁵ and 2.0 × 10⁶ syngeneic HCC cells, respectively. Longitudinal (T1) relaxation time- and transverse (T2) relaxation time-weighted MR images were acquired.

RESULTS

The three-dimensional (3D) T1-weighted gradient echo had 0.35-mm isotropic resolution allowing accurate semi-automatic volume segmentation. 2D T2-weighted imaging provided high tumor contrast. Segmentation of combined 3D gradient echo T1-weighted images and 2D turbo spin echo T2-weighted images provided excellent correlation with histology (y = 0.866x + 0.034, R² = 0.997 p < .0001) and with α-fetoprotein (y = 0.736x + 1.077, R² = 0.976, p < .0001). There was robust inter- and intra-observer reproducibility (intra-class correlation coefficient > 0.998, p < .0001).

CONCLUSIONS

We have developed a novel, noninvasive contrast imaging protocol which enables semi-automatic 3D volume quantification to analyze nonspherical tumor nodules and to follow up the growth of tumor nodules over time.

Renal zoomed EPI-DWI with spatially-selective radiofrequency excitation pulses in two dimensions

PURPOSE

To evaluate the feasibility and clinical robustness of zoomed diffusion-weighted echo planar imaging (z-EPI) relative to conventional single-shot EPI (c-EPI) for DWI of the kidneys.

MATERIALS AND METHODS

This retrospective study was approved by the institutional research ethics board. 66 patients (median age 58.5 years±13.4, range 23-83 years, 45 men, 21 women) undergoing 3T (Magnetom Skyra(®), Siemens Healthcare, Erlangen, Germany) using a dynamic parallel transmit array (TimTX TrueShape, Siemens Healthcare, Erlangen, Germany) for renal MRI were included in this study. Both c-EPI and z-EPI images were obtained. For z-EPI, a two-dimensional spatially-selective radiofrequency (RF) pulse was applied for echo planar imaging with the FOV reduced by a factor of 3. Two radiologists, blinded to clinical data and scan parameters evaluated the images with respect to their diagnostic confidence, overall preference, overall image quality, delineation of the kidney, spatial distortion, and image blur. Sequences were compared using a paired Wilcoxon test. ADC values for the upper pole, mid-zone, lower pole of the normal kidneys were compared between sequences as well as ADC values for renal lesions, using a paired t-test.

RESULTS

With z-EPI, the kidney was significantly better delineated with sharper boundaries, less image blur and distortion, and overall better image quality relative to c-EPI (all p<0.001). The z-EPI technique led to greater diagnostic confidence than c-EPI (p=0.020). z-EPI was preferred to c-EPI in 60 cases (90.9%, 60/66). No statistically significant differences in the ADC values of renal parenchyma or of renal lesions were observed between the two sequences (all p>0.05).

CONCLUSION

Image quality, distortion, and susceptibility artifacts might be improved by using z-EPI rather than c-EPI for DWI of the kidney.

New Magnetic Resonance Imaging Index for Renal Fibrosis Assessment: A Comparison between Diffusion-Weighted Imaging and T1 Mapping with Histological Validation

A need exists to noninvasively assess renal interstitial fibrosis, a common process to all kidney diseases and predictive of renal prognosis. In this translational study, Magnetic Resonance Imaging (MRI) T1 mapping and a new segmented Diffusion-Weighted Imaging (DWI) technique, for Apparent Diffusion Coefficient (ADC), were first compared to renal fibrosis in two well-controlled animal models to assess detection limits. Validation against biopsy was then performed in 33 kidney allograft recipients (KARs). Predictive MRI indices, ΔT1 and ΔADC (defined as the cortico-medullary differences), were compared to histology. In rats, both T1 and ADC correlated well with fibrosis and inflammation showing a difference between normal and diseased kidneys. In KARs, MRI indices were not sensitive to interstitial inflammation. By contrast, ΔADC outperformed ΔT1 with a stronger negative correlation to fibrosis (R² = 0.64 against R² = 0.29 p < 0.001). ΔADC tends to negative values in KARs harboring cortical fibrosis of more than 40%. Using a discriminant analysis method, the ΔADC, as a marker to detect such level of fibrosis or higher, led to a specificity and sensitivity of 100% and 71%, respectively. This new index has potential for noninvasive assessment of fibrosis in the clinical setting.

Improve the image quality of orbital 3 T diffusion-weighted magnetic resonance imaging with readout-segmented echo-planar imaging

The aim of our study is to compare the image quality of readout-segmented echo-planar imaging (rs-EPI) and that of standard single-shot EPI (ss-EPI) in orbital 3 T diffusion-weighted (DW) magnetic resonance (MR) imaging in healthy subjects. Forty-two volunteers underwent two sets of orbital DW imaging scan at a 3 T MR unit, and image quality was assessed qualitatively and quantitatively. As a result, we found that rs-EPI could provide better image quality than standard ss-EPI, while no significant difference was found on the apparent diffusion coefficient between the two sets of DW images.

Body Diffusion-weighted MR Imaging in Oncology: Imaging at 3 T

Advances in hardware and software enable high-quality body diffusion-weighted images to be acquired for oncologic assessment. 3.0 T affords improved signal/noise for higher spatial resolution and smaller field-of-view diffusion-weighted imaging (DWI). DWI at 3.0 T can be applied as at 1.5 T to improve tumor detection, disease characterization, and the assessment of treatment response. DWI at 3.0 T can be acquired on a hybrid PET-MR imaging system, to allow functional MR information to be combined with molecular imaging.

Readout-segmented echo-planar imaging in diffusion-weighted imaging of the kidney: comparison with single-shot echo-planar imaging in image quality

OBJECTIVE

The purpose of this study was to compare the image quality of readout-segmented echo-planar imaging (RS-EPI) and that of standard single-shot echo-planar imaging (SS-EPI) in the kidney in a rat model.

MATERIALS AND METHODS

Twelve Wistar rats undergoing MRI examinations were imaged with two diffusion-weighted (DW) imaging protocols: a standard SS-EPI and a new RS-EPI protocol, both with a 1.0 × 1.0 × 3.0 mm voxel. The two groups of diffusion-weighted images were independently scored on geometric distortion, image blurring, signal dropout, and the overall image quality by two radiologists. Signal-to-noise ratio (SNR) and apparent diffusion coefficient (ADC) were measured on both sequences. Inter-rater agreement (IRA) was evaluated by Fleiss kappa (κ) and inter-class correlation coefficient (ICC) statistics. Comparisons of image qualities were made by Wilcoxon signed-rank test and paired-sample t test.

RESULTS

Both RS-EPI and SS-EPI had good IRAs in scoring image qualities (κ = 0.607-0.833) and measuring renal ADCs (ICC = 0.828-0.945). Compared to SS-EPI, RS-EPI produced less geometric distortion (median score 1.5 versus 2.5, p < 0.0001), less image blurring (1.75 versus 2.0, p = 0.0003), less signal dropout (1.0 versus 3.0, p = 0.0001), and a lower score in overall image artifacts (4.25 versus 7.25; p < 0.0001). RS-EPI had higher SNR of renal DW images than SS-EPI (p < 0.001). The intra-variability of ADCs in cortex, outer medulla, and inner medulla ranged from 9.6% to 11.1% (Pearson correlation coefficient ρ = 0.675-0.729; p < 0.001) between the two protocols.

CONCLUSION

We showed that for DWI of the kidney at 1.0 × 1.0 × 3.0 mm(3) voxel sizes, the new protocol provided better image quality than standard SS-EPI protocol.