Renal MRI: From Nephron to NMR Signal

Renal diseases pose a significant socio-economic burden on healthcare systems. The development of better diagnostics and prognostics is well-recognized as a key strategy to resolve these challenges. Central to these developments are MRI biomarkers, due to their potential for monitoring of early pathophysiological changes, renal disease progression or treatment effects. The surge in renal MRI involves major cross-domain initiatives, large clinical studies, and educational programs. In parallel with these translational efforts, the need for greater (patho)physiological specificity remains, to enable engagement with clinical nephrologists and increase the associated health impact. The ISMRM 2022 Member Initiated Symposium (MIS) on renal MRI spotlighted this issue with the goal of inspiring more solutions from the ISMRM community. This work is a summary of the MIS presentations devoted to: 1) educating imaging scientists and clinicians on renal (patho)physiology and demands from clinical nephrologists, 2) elucidating the connection of MRI parameters with renal physiology, 3) presenting the current state of leading MR surrogates in assessing renal structure and functions as well as their next generation of innovation, and 4) describing the potential of these imaging markers for providing clinically meaningful renal characterization to guide or supplement clinical decision making. We hope to continue momentum of recent years and introduce new entrants to the development process, connecting (patho)physiology with (bio)physics, and conceiving new clinical applications. We envision this process to benefit from cross-disciplinary collaboration and analogous efforts in other body organs, but also to maximally leverage the unique opportunities of renal physiology. LEVEL OF EVIDENCE: 1 TECHNICAL EFFICACY STAGE: 2.

Temporospatial Feathering of Hot Spots for Computed Tomography-Guided Stereotactic Adaptive Radiotherapy (CT-STAR) for the Ultra-Central Thorax

PURPOSE/OBJECTIVE(S)

SBRT to the ultra-central thorax is limited by potential toxicity. It has been demonstrated that exposing proximal bronchial tree or pulmonary arteries to high dose per fraction (fx) treatment may induce bronchopulmonary hemorrhage, amongst other serious complications. Online adaptive radiotherapy is a technique that adjusts a treatment plan to the anatomy-of-the-day and benefits have been demonstrated in ultra-central thoracic disease. In addition, feathering is a treatment planning technique that generates several plans to avoid consistent organ-at-risk (OAR) doses throughout treatment. With daily adaptation, it may be possible to adjust the position of a hot spot (>120% prescription (Rx)) within the tumor each fx (temporospatial feathering) while respecting hard OAR constraints. We investigated the feasibility and plan quality of using CBCT-guided stereotactic adaptive radiotherapy (CT-STAR) for ultra-central lung tumors with hotspot temporospatial feathering.

MATERIALS/METHODS

Seven patients with ultra-central thoracic disease (6 patients with parenchymal tumors in contact with the trachea, proximal bronchial tree, great vessels, esophagus, or heart; 1 patient with a subcarinal lymph node) receiving standard of care radiotherapy were enrolled on an imaging study. An in-silico planning study first generated an SBRT plan (in silico Rx: 55 Gy in 5fx) that used a GTV_OPT (GTV minus OAR plus a safety margin) to optimize the location of the plan hotspot. Five spherical boost structures were manually created inside of the GTV_OPT structure. The same planning template was used except the boost structures were iteratively used in plan optimization instead of the GTV_OPT structure, to simulate the five CT-STAR fx hotspot temporospatially feathering. The five-plan composite was compared to the initial plan.

RESULTS

All plans generated met strict OAR constraints. Table 1 shows the mean difference in PTV, GTV, and OARs percent coverage by various isodose levels. Feathering the hotspot had negligible impact on target coverage by 50 Gy and 55 Gy isodose lines as well as OAR doses compared to the base SBRT plan. The feathered plan sum resulted in 14.7% increase in V66 Gy of the GTV. One patient saw a decrease in V66 Gy coverage to all target structures, though V50 Gy and V55 Gy were not affected.

CONCLUSION

We demonstrated the feasibility and utility of temporospatially adapting the hotspot for central lung SBRT, which safely increases the amount of tumor receiving more than 120% Rx.

Preliminary analysis: Background parenchymal 18F-FDG uptake in breast cancer patients appears to correlate with background parenchymal enhancement and to vary by distance from the index cancer

PURPOSE

To investigate how breast parenchymal uptake (BPU) of 18F-FDG on positron emission tomography/ magnetic resonance imaging (PET/MRI) in patients with breast cancer is related to background parenchymal enhancement (BPE), amount of fibroglandular tissue (FGT), and age, as well as whether BPU varies as a function of distance from the primary breast cancer.

MATERIALS AND METHODS

In this institutional review board (IRB)-approved retrospective study, 40 patients (all female, ages 32-80 years, mean 52 years) gave informed consent prior to undergoing contrast enhanced breast PET/MRI from 3/2015 to 2/2018. Of the 40 patients, 6 were excluded for multicentric or bilateral cancers, 1 for current lactation and 6 because the raw data from their scans were corrupted. The remaining 27 patients (all female, ages 33 to 80 years, mean age 53 years) comprised the study population. Prone PET and contrast-enhanced MR data were acquired simultaneously on a 3-T integrated PET/ MR system. BPU was measured as SUVmax of a 1.5 cm³ volume of interest 1) in the same quadrant of the ipsilateral breast, 5 mm from the index lesion; 2) in the opposite quadrant of the ipsilateral breast; and 3) in contralateral breast, quadrant matched to the opposite quadrant of the ipsilateral breast. The maximum standardized uptake value (SUVmax) of the index cancer was measured using a VOI that included the entire volume of the index lesion. Bleed from the primary tumor was corrected for (PET edge, MIM). FGT and BPE was assessed by 2 readers on a 4-point scale in accordance with BI-RADS lexicon. The Wilcoxon signed rank test and the Spearman rank correlation test were performed.

RESULTS

BPU was significantly greater in the same quadrant as the breast cancer as compared with the opposite quadrant of the same breast (p < 0.001 for both readers) and was significantly greater in the opposite quadrant of the same breast compared to the matched quadrant of the contralateral breast (p = 0.002 for reader 1 and <0.001 for reader 2). While the FGT SUVmax in the same quadrant as the cancer correlated significantly with SUVmax of the index lesion, the FGT SUVmax in the opposite quadrant of the same breast and in the matched quadrant of the contralateral breast did not. The FGT SUVmax in the contralateral breast positively correlated with the degree of BPE and negatively correlated with age, but did not show a significant correlation with the amount of FGT for either reader.

CONCLUSION

There appears to be an inverse correlation between metabolic activity of normal breast parenchyma and distance from the index cancer. BPU significantly correlates with BPE.

Health-related parental indicators and their association with healthy weight and overweight/obese children's physical activity

Background

Although it is accepted that parents play a key role in forming children’s health behaviours, differences in parent-child physical activity (PA) have not previously been analysed simultaneously in random samples of families with non-overweight and overweight to obese preschool and school-aged children. This study answers the question which of the health-related parental indicators (daily step count (SC), screen time (ST), and weight status and participation in organized leisure-time PA) help their children achieve the step count recommendations.

Methods

A nationally representative sample comprising 834 families including 1564 parent-child dyads who wore the Yamax Digiwalker SW-200 pedometer for at least 8 h a day on at least four weekdays and both weekend days and completed a family log book (anthropometric parameters, SC, and ST). Logistic regression analyses were used to investigate whether parental achievement of the daily SC recommendation (10,000 SC/day), non-excessive ST (< 2 h/day), weight status, and active participation in organized PA were associated with children’s achievement of their daily SC (11,500 SC/day for pre-schoolers and 13,000/11,000 SC/day for school-aged boys/girls).

Results

While living in a family with non-overweight parents helps children achieve the daily SC recommendation (mothers in the model: OR = 3.50, 95% CI = 2.29–5.34, p < 0.001; fathers in the model: OR = 2.41, 95% CI = 1.37–4.26, p < 0.01) regardless of their age category, gender, or ST, for families with overweight/obese children, only the mother’s achievement of the SC recommendations and non-excessive ST significantly (p < 0.05) increase the odds of their children reaching the daily SC recommendation. The active participation of children in organized leisure-time PA increases the odds of all children achieving the daily SC recommendations (OR = 1.80–2.85); however, for overweight/obese children this remains non-significant. The participation of parents in organized leisure-time PA does not have a significant relationship to the odds of their overweight/obese or non-overweight children achieving the daily SC recommendations.

Conclusions

The mother’s health-related behaviours (PA and ST) significantly affect the level of PA of overweight/obese preschool and school-aged children. PA enhancement programmes for overweight/obese children cannot rely solely on the active participation of children in organized leisure-time PA; they also need to take other family-based PA, especially at weekends, into account.

Diffusion-weighted imaging outside the brain: Consensus statement from an ISMRM-sponsored workshop

The significant advances in magnetic resonance imaging (MRI) hardware and software, sequence design, and postprocessing methods have made diffusion-weighted imaging (DWI) an important part of body MRI protocols and have fueled extensive research on quantitative diffusion outside the brain, particularly in the oncologic setting. In this review, we summarize the most up-to-date information on DWI acquisition and clinical applications outside the brain, as discussed in an ISMRM-sponsored symposium held in April 2015. We first introduce recent advances in acquisition, processing, and quality control; then review scientific evidence in major organ systems; and finally describe future directions. J. Magn. Reson. Imaging 2016;44:521-540.

A model-based reconstruction for undersampled radial spin-echo DTI with variational penalties on the diffusion tensor

Radial spin-echo diffusion imaging allows motion-robust imaging of tissues with very low T2 values like articular cartilage with high spatial resolution and signal-to-noise ratio (SNR). However, in vivo measurements are challenging, due to the significantly slower data acquisition speed of spin-echo sequences and the less efficient k-space coverage of radial sampling, which raises the demand for accelerated protocols by means of undersampling. This work introduces a new reconstruction approach for undersampled diffusion-tensor imaging (DTI). A model-based reconstruction implicitly exploits redundancies in the diffusion-weighted images by reducing the number of unknowns in the optimization problem and compressed sensing is performed directly in the target quantitative domain by imposing a total variation (TV) constraint on the elements of the diffusion tensor. Experiments were performed for an anisotropic phantom and the knee and brain of healthy volunteers (three and two volunteers, respectively). Evaluation of the new approach was conducted by comparing the results with reconstructions performed with gridding, combined parallel imaging and compressed sensing and a recently proposed model-based approach. The experiments demonstrated improvements in terms of reduction of noise and streaking artifacts in the quantitative parameter maps, as well as a reduction of angular dispersion of the primary eigenvector when using the proposed method, without introducing systematic errors into the maps. This may enable an essential reduction of the acquisition time in radial spin-echo diffusion-tensor imaging without degrading parameter quantification and/or SNR.

Self-reported recurrent pain and medicine use behaviours among 15-year olds: results from the international study

BACKGROUND

There is considerable variation in adolescent pain prevalence across epidemiological studies, with limited information on pain-related behaviours among adolescents, including medicine use. The aims of this study were (1) to examine the prevalence of recurrent pain among 15-year-old adolescents internationally; (2) to investigate the association between recurrent pain and medicine use behaviours among boys and girls; and (3) to evaluate the consistency of these associations across countries.

METHODS

The World Health Organization (WHO) collaborative international Health Behaviour in School-aged Children 2009/2010 study collects data about self-reported aches and medicine use from 36,762 15-year-old adolescents from 22 countries/regions in Europe and the United States. Multi-level multivariate logistic regression, stratified by gender, was used to analyse the association between recurrent pain and medicine use for headache, stomachache, nervousness and difficulties in getting to sleep.

RESULTS

More than 30% of adolescents reported recurrent headache, almost 30% recurrent backache and approximately 20% recurrent stomachache. Although pain prevalence and medicine use for aches were much higher for girls, the association between pain and medicine use was similarly strong for both genders. Adolescents with recurrent pain are more likely to use medicines also for non-corresponding pain, nervousness and difficulties in getting to sleep. The association between recurrent pain and medicine use was consistent across countries despite large-country differences in the prevalence of recurrent pain and medicine use.

CONCLUSIONS

Recurrent pain in adolescence is common cross-nationally. Adolescents with recurrent pain are more likely to use medicine in general. Recurrent pain and medicine use should be addressed in adolescent health policies.

Changes in physical activity in pre-schoolers and first-grade children: longitudinal study in the Czech Republic

BACKGROUND

The transition from kindergarten to first year at school is associated with a variety of psychosocial changes in children. The aim of this longitudinal study was to identify the changes in children's physical activity (PA) upon entry to first year at school; and to identify the days of the school week that exhibit low PA.

METHODS

We monitored the PA levels of 176 children twice: initially in kindergarten and again in first-year classes at school. The age (mean +/- standard deviation) of children at kindergarten was 5.7 +/- 0.5 years and 6.7 +/- 0.5 years at the first year of elementary school. We evaluated PA employing the activity energy expenditure (AEE - kcal/kg/day) from Caltrac accelerometer and daily amount of steps (STEPS) from Yamax pedometer. Participants were monitored over 7 days to include a weekend.

RESULTS

The mean AEE was 11.5 in pre-school girls and 12.9 kcal/kg/day in boys; and STEPS were 9923 steps/day in girls and 11 864 in boys on weekdays. At weekends, it was 11.5 kcal/kg/day in girls and 12.7 kcal/kg/day in boys and 10 606 steps/day in girls and 11 182 steps/day in boys. The mean AEE and STEPS in first-grade girls and boys was 9.9 and 9.8 kcal/kg/day respectively, and 7911 and 8252 steps/day respectively on weekdays, and 8.8 and 9.0 kcal/kg/day and 6872 and 7194 steps/day respectively at weekends. First-grade school children had significantly lower PA than pre-school children on weekdays (P < 0.0001) and at weekends (P < 0.0001). Decline in PA on weekdays was during time spent at school (P < 0.0001) and not during after-school children's leisure time.

CONCLUSION

The parts of the week when first-grade school children show low PA are the times spent in lessons and in after-school nursery and at weekends. PA needs to be promoted using intervention programmes mainly during the after-school nursery programmes and at weekends.