New and Emerging Applications of Magnetic Resonance Elastography of Other Abdominal Organs

Understanding and measuring mechanical signals in the tumor stroma

The tumor microenvironment (TME) is well known for its immune suppressive role, especially in solid tumors which are characterized by a thick, dense stroma. Apart from cell-cell interactions and biochemical signals, the tumor stroma is also characterized by its distinct mechanical properties, which are dictated by the composition and architecture of its extracellular matrix (ECM). Cancer-associated fibroblasts (CAFs) are the main producers and remodelers of the stromal ECM, and their heterogeneity has recently become a focus of intense research. This review describes recent findings highlighting CAF subtypes and their specific functions, as well as the development of 3D models to study tumor stroma mechanics in vitro. Finally, we discuss the quantitative techniques used to measure tissue mechanical properties at different scales. Given the diagnostic and prognostic value of stroma stiffness and composition, and the recent development of anti-tumor therapeutic strategies targeting the stroma, understanding and measuring tumor stroma mechanical properties has never been more timely or relevant.

Postprandial splenic stiffness changes on magnetic resonance elastography in a young healthy population

Magnetic resonance elastography (MRE) is an accurate noninvasive diagnostic tool for assessing the stiffness of parenchymal organs, including the spleen. However, this measurement may be biased due to postprandial changes in splenic stiffness. The aim of the current study was to evaluate postprandial changes in spleen stiffness assessed by MRE in a large sample of healthy volunteers. This was a prospective institutional research ethics board-approved study. Healthy volunteers with no history of liver disease were recruited for an MRE test and blood draw from December 2018 to July 2019. Each participant underwent spleen MRE after at least 4 h of fasting and again 30 min after a 1000 kcal meal. Also, 14 randomly selected volunteers underwent additional MRE examinations at 1.5 and 2.5 h after food intake. The MRE data were acquired at 60 Hz using a 1.5-T MRI scanner. The spleen stiffness was assessed using a weighted mean of stiffness values from regions of interest manually drawn on three to five spleen slices. Spearman's rank correlation, Wilcoxon signed-rank, Friedman, and Mann-Whitney tests were used for statistical analysis. A total of 100 volunteers met the inclusion criteria and were eventually enrolled in this study (age 23 ± 2 years; 65 women). The mean spleen stiffness for the whole group increased by 7.9% (p < 0.001) from the mean ± SD value of 5.09 ± 0.63 (95% CI: 4.96-5.21) kPa in the fasting state to 5.47 ± 0.66 (95% CI 5.34-5.60) kPa 30 min after the meal and then gradually decreased. However, even 2 h 30 min after the meal, the spleen stiffness was higher than in the fasting state. This difference was statistically significant at p less than 0.001. It was concluded that meal intake results in a statistically significant elevation of spleen stiffness that persists for 2.5 h. This finding supports the recommendation for routine fasting for more than 2.5 h prior to assessing MRE-based spleen stiffness.

Evaluation of Spleen Stiffness in Young Healthy Volunteers Using Magnetic Resonance Elastography

PURPOSE

Magnetic resonance elastography (MRE) has been established as the most accurate noninvasive technique for diagnosing liver fibrosis. Recent publications have suggested that the measurement of splenic stiffness is useful in setting where portal hypertension may be present. The goal of the current study was to compile normative data for MRE-assessed stiffness measurements of the spleen in young adults.

MATERIALS AND METHODS

A total of 100 healthy young Caucasian volunteers (65 females and 35 males) in the age range of 20 to 32 years were enrolled in this study. The participants reported no history of chronic spleen and liver disease, normal alcohol consumption, and a normal diet. The MRE data were acquired by using a 1.5 T whole-body scanner and a 2D GRE pulse sequence with 60 Hz excitation. Spleen stiffness was calculated as a weighted mean of stiffness values in the regions of interest manually drawn by the radiologist on three to five spleen slices.

RESULTS

Mean spleen stiffness was 5.09 ± 0.65 kPa for the whole group. Male volunteers had slightly higher splenic stiffness compared to females: 5.28 ± 0.78 vs. 4.98 ± 0.51 kPa, however, this difference was not statistically significant (p = 0.12). Spleen stiffness did not correlate with spleen fat content and liver stiffness but a statistically significant correlation with spleen volume was found.

CONCLUSIONS

The findings of this study provide normative values for 2D MRE-based measurement of spleen stiffness in young adults, a basis for assessing the value of this biomarker in young patients with portal system pathologies.

Abdominal MR elastography with multiple driver arrays: performance and repeatability

PURPOSE

To evaluate the performance and repeatability assessing liver, spleen, and kidney stiffness with magnetic resonance elastography (MRE), using arrays of pneumatic passive drivers.

METHODS

An array of four flexible, pneumatically activated passive drivers for abdominal MRE were developed and tested in this study. Multiple MRE acquisitions were performed prospectively in a series of eleven volunteers, with activation of all combinations of the four drivers, individually and simultaneously. MRE exams were repeated three times to study within-day and between-day test-retest repeatability. Semi-quantitative evaluation of wave propagation and penetration, and quantitative assessment of tissue stiffness was conducted for liver, spleen, and kidneys.

RESULTS

When driver location and amplitude were sufficient to achieve necessary shear wave illumination in any given region of interest, the results showed excellent test-retest repeatability in abdominal organ stiffness with both single and multiple driver configurations. The results confirmed that multiple driver arrays provided suitable shear wave illumination over a larger region of the abdomen, allowing more reliable stiffness measurements in multiple organs. MRE assessment of the spleen was found to be prone to effects of excessive shear wave amplitude, however.

CONCLUSION

A multiple driver array provides shear wave illumination over a larger region of the abdomen than obtained with a single driver, for MRE assessment of multiple abdominal organs, providing excellent test-retest repeatability in stiffness measurements. However, careful tuning of the location and amplitude of each driver is essential to achieve consistent results.

Multiparametric Magnetic Resonance Imaging of the Kidneys: Effects of Regional, Side, and Hydration Variations on Functional Quantifications

BACKGROUND

To standardize renal functional magnetic resonance imaging (MRI), it is important to understand the influence of side-to-side variation, regional variation within the organ, and hydration states in MRI and to search for variables that are not affected by those variations.

PURPOSE

To assess MRI-based biomarkers for characterizing the kidney in healthy volunteers while considering variations in anatomic factors and hydration states.

STUDY TYPE

Prospective.

SUBJECTS

Twenty-five healthy volunteers (15 females and 10 males, median age 25 years).

FIELD STRENGTH/SEQUENCE

3.0 T intravoxel incoherent motion diffusion-weighted imaging, arterial spinning labeling imaging, blood oxygenation level dependent imaging, and three-dimensional MR elastography.

ASSESSMENT

Functional variables were measured before and after water challenge. Regions of interest were manually drawn by two investigators (JC and ZZ, with 8- and 5-year experiences in abdominal radiology) in the cortex, the medulla, and the entire kidney. The medulla/cortex ratio was calculated.

STATISTICAL TESTS

Paired t-test or Wilcoxon signed rank test; interobserver correlation coefficient; repeatability coefficients; Spearman's correlation; significance level: P < 0.05.

RESULTS

Diffusion parameters were only subject to regional variation. R2*, RBF, and renal stiffness (RS) showed regional variation, side variation, and dependence on hydration states. For each side and hydration state, the cortex showed significantly higher standard apparent diffusion coefficient (sADC), higher true diffusion (D), lower R2*, and lower RS than the medulla. For each region at baseline, the left kidney showed significantly higher R2*, higher RS, and lower renal blood flow (RBF) than the right kidney. For each region and side, RS and RBF increased significantly while R2* decreased significantly after water intake. After introducing the intrinsic regional difference, significantly higher medulla/cortex ratio of RS remained after water intake except for RS@90 Hz in the right kidney.

DATA CONCLUSION

Renal multiparametric MRI quantifications were affected by regional variation, side variation, and hydration states.

LEVEL OF EVIDENCE

2 TECHNICAL EFFICACY: Stage 1.

Magnetic resonance elastography: from invention to standard of care

In 1995, a vivid image of diffracting waves in red and blue was published on the cover of the journal SCIENCE. An article in that issue described a new imaging technology called magnetic resonance elastography (MRE) (Muthupillai in Science 269:1854-1857, 1995). In 2004, quantitative images of liver stiffness in vivo, obtained with MRE, were demonstrated for the first time at the annual meeting of the International Society for Magnetic Resonance in Medicine. Only five years later, the technology had become widely available as an FDA-cleared diagnostic tool for patient care. MRE has emerged as a reliable non-invasive diagnostic method for detecting and staging liver fibrosis. Deployed on more than 2000 MRI systems worldwide, MRE has received a Category I CPT code from the American Medical Association, based on clinical availability and efficacy. For many patients, MRE now provides a safe, more comfortable, and much less expensive alternative to liver biopsy for diagnosing liver fibrosis. Although progress in radiology is notable for a history of very rapid translation of technology innovations to patient care, the path is rarely linear. This article reflects on the story of MRE, the advances and the setbacks, and the lessons that were learned in the process.

Evaluation of MR elastography for prediction of lymph node metastasis in prostate cancer

PURPOSE

To assess the relationship between MRE stiffness of prostate cancer (PCa) and the extent of lymph node metastasis (LNM) in patients with PCa undergoing radical prostatectomy (RP) and extended pelvic lymph node dissection (ePLND).

MATERIALS

The local institutional review board approved this retrospective study. We retrospectively analyzed 49 patients, who had undergone MRE, mpMRI and pelvic MRI on a 3.0 T MRI scanner, with histopathological confirmed PCa after RP (from June 2015 to December 2019). For each patient, preoperative clinical data and characteristics of MRE, mpMRI and pelvic MRI were recorded. Independent-samples t test, univariate and multivariate logistic regression analyses were performed. And receiver operating characteristic (ROC) analysis were performed to compare the diagnostic performances of multivariate models with the Briganti 2019 nomogram.

RESULTS

PCa MRE stiffness and maximum diameter were independent predictors of LNM. When PCa MRE stiffness at 60 Hz (odds ratio [OR] = 20.223, P = 0.013) and maximum diameter (OR = 4.575, P = 0.046) were combined, the sensitivity and specificity were 100% and 91.9% to predict LNM. When PCa MRE stiffness at 90 Hz (OR = 7.920, P = 0.013) and maximum diameter (OR = 2.810, P = 0.045) were combined, the sensitivity and specificity were 100% and 86.5% to predict LNM. The areas under curves (AUCs) of the combinations were higher than the AUC of the Briganti 2019 nomogram (0.982 vs. 0.904, P = 0.040 [60 Hz]; 0.975 vs. 0.904, P = 0.060 [90 Hz], respectively).

CONCLUSIONS

MRE-based assessment of PCa stiffness may be useful for predicting LNM of PCa preoperatively and noninvasively.

Advanced and futuristic approaches for breast cancer diagnosis

Background

Breast cancer is the most frequent cancer and one of the most common causes of death in women, impacting almost 2 million women each year. Tenacity or perseverance of breast cancer in women is very high these days with an extensive increasing rate of 3 to 5% every year. Along with hurdles faced during treatment of breast tumor, one of the crucial causes of delay in treatment is invasive and poor diagnostic techniques for breast cancer hence the early diagnosis of breast tumors will help us to improve its management and treatment in the initial stage.

Main body

Present review aims to explore diagnostic techniques for breast cancer that are currently being used, recent advancements that aids in prior detection and evaluation and are extensively focused on techniques that are going to be future of breast cancer detection with better efficiency and lesser pain to patients so that it helps to a physician to prevent delay in treatment of cancer. Here, we have discussed mammography and its advanced forms that are the need of current era, techniques involving radiation such as radionuclide methods, the potential of nanotechnology by using nanoparticle in breast cancer, and how the new inventions such as breath biopsy, and X-ray diffraction of hair can simply use as a prominent method in breast cancer early and easy detection tool.

Conclusion

It is observed significantly that advancement in detection techniques is helping in early diagnosis of breast cancer; however, we have to also focus on techniques that will improve the future of cancer diagnosis in like optical imaging and HER2 testing.

Is Ultrasound Elastography Useful in Predicting Clinically Relevant Pancreatic Fistula After Pancreatic Resection?: A Systematic Review and Meta-analysis

OBJECTIVES

Ultrasound (US) elastography has been proposed for the non-invasive prediction of clinically relevant pancreatic fistula (CR-POPF) in patients undergoing pancreatic resection. We aimed to perform a systematic review with meta-analysis to assess the diagnostic value of US elastography in predicting CR-POPF.

METHODS

MEDLINE via PubMed, Ovid Embase, Scopus, and Cochrane Library databases, and abstracts of international conference proceedings were searched up to April 20, 2020. Studies assessing the performance of abdominal US elastography in predicting CR-POPF in patients undergoing pancreatic resection were included. The quality of the studies was assessed using Quality Assessment of Diagnostic Accuracy Studies.

RESULTS

Five studies, including 247 patients who underwent partial pancreatic resection of whom 72 patients experiencing CR-POPF, were selected. All studies performed US elastography in different pancreatic sites. The pooled mean strain value was lower in pancreatic segments of patients experiencing CR-POPF than in those without, with a pooled weighted mean difference of -0.187 (95% confidence intervals, -0.303 to -0.071; P = 0.002). There was low heterogeneity between studies (I = 7.6%), and all studies were at "high risk" or "unclear risk" of bias.

CONCLUSIONS

This study provides evidence that US elastography values are statistically significantly lower in patients experiencing CR-POPF.