Placental differences between uncomplicated and complicated monochorionic diamniotic pregnancies on diffusion and multicompartment Magnetic Resonance Imaging

INTRODUCTION

Twin-twin transfusion syndrome (TTTS) and selective fetal growth restriction (sFGR) are common complications in monochorionic diamniotic (MCDA) pregnancies. The Diffusion-rElaxation Combined Imaging for Detailed Placental Evaluation (DECIDE) model, a placental-specific model, separates the T2 values of the fetal and maternal blood from the background tissue and estimates the fetal blood oxygen saturation. This study investigates diffusion and relaxation differences in uncomplicated MCDA pregnancies and MCDA pregnancies complicated by TTTS and sFGR in mid-pregnancy.

METHODS

This prospective monocentric cohort study included uncomplicated MCDA pregnancies and pregnancies complicated by TTTS and sFGR. We performed MRI with conventional diffusion-weighted imaging (DWI) and combined relaxometry - DWI-intravoxel incoherent motion. DECIDE analysis was used to quantify different parameters within the placenta related to the fetal, placental, and maternal compartments.

RESULTS

We included 99 pregnancies, of which 46 were uncomplicated, 12 were complicated by sFGR and 41 by TTTS. Conventional DWI did not find differences between or within cohorts. On DECIDE imaging, fetoplacental oxygen saturation was significantly lower in the smaller member of sFGR (p = 0.07) and in both members of TTTS (p = 0.01 and p = 0.004) compared to the uncomplicated pairs. Additionally, average T2 relaxation time was significantly lower in the smaller twin of the sFGR (p = 0.004) compared to the uncomplicated twins (p = 0.03).

CONCLUSION

Multicompartment functional MRI showed significant differences in several MRI parameters between the placenta of uncomplicated MCDA pregnancies and those complicated by sFGR and TTTS in mid-pregnancy.

Application of Automatic Segmentation on Super-Resolution Reconstruction MR Images of the Abnormal Fetal Brain

BACKGROUND AND PURPOSE

Fetal brain MR imaging is clinically used to characterize fetal brain abnormalities. Recently, algorithms have been proposed to reconstruct high-resolution 3D fetal brain volumes from 2D slices. By means of these reconstructions, convolutional neural networks have been developed for automatic image segmentation to avoid labor-intensive manual annotations, usually trained on data of normal fetal brains. Herein, we tested the performance of an algorithm specifically developed for segmentation of abnormal fetal brains.

MATERIALS AND METHODS

This was a single-center retrospective study on MR images of 16 fetuses with severe CNS anomalies (gestation, 21-39 weeks). T2-weighted 2D slices were converted to 3D volumes using a super-resolution reconstruction algorithm. The acquired volumetric data were then processed by a novel convolutional neural network to perform segmentations of white matter and the ventricular system and cerebellum. These were compared with manual segmentation using the Dice coefficient, Hausdorff distance (95th percentile), and volume difference. Using interquartile ranges, we identified outliers of these metrics and further analyzed them in detail.

RESULTS

The mean Dice coefficient was 96.2%, 93.7%, and 94.7% for white matter and the ventricular system and cerebellum, respectively. The Hausdorff distance was 1.1, 2.3, and 1.6 mm, respectively. The volume difference was 1.6, 1.4, and 0.3 mL, respectively. Of the 126 measurements, there were 16 outliers among 5 fetuses, discussed on a case-by-case basis.

CONCLUSIONS

Our novel segmentation algorithm obtained excellent results on MR images of fetuses with severe brain abnormalities. Analysis of the outliers shows the need to include pathologies underrepresented in the current data set. Quality control to prevent occasional errors is still needed.

Robustness of T1 and ECV mapping radiomics features: a between-session evaluation in young athletes

Funding Acknowledgements

Type of funding sources: None.

Introduction

Radiomics of cardiac MRI T1, T2 and extracellular volume (ECV) maps has the potential to add biomarkers that can aid in the detection and diagnosis of myocardial diseases. Recently, the feasibility of CMR mapping based radiomics to classify various myocardial diseases was demonstrated [1-6]. However, reproducibility studies have reported sensitivity of radiomics to acquisition parameters and processing steps involved concluding that only a limited number of features may be reproducible [7-8]. As CMR mapping guidelines recommend to use site-specific normal values [9], radiomics features derived likely also need careful site-specific evaluation to benchmark disease-related feature alterations.

Purpose

We aimed to assess the between-session reproducibility of radiomics features in a longitudinal dataset of MOLLI T1 and ECV maps obtained in young athletes at 1.5T.

Materials and methods

This study included data from 17 healthy subjects (15-20y; informed consent obtained) with data acquired two years apart [10] considered for this purpose as test-retest data since a prior standard analysis showed near identical average T1 (t1: 977±16 ms, t2: 982±20ms) and ECV (t1: 23.4±1.3%, t2: 23.4±1.5%). T1 mapping data was acquired on a 1.5T system (Ingenia, Philips) using MOLLI 5s(3s)3s. After motion correction and T1 and ECV map calculation [11], the left ventricular myocardium was manually delineated by two readers independently (3D Slicer [12]). In total 44 images (short and long axis) were included for each time point. The radiomics analysis resulted in 96 features per image (7 feature families, ‘shape’ excluded; no filters applied; Pyradiomics, [13]). The concordance correlation coefficient (CCC) was calculated to assess reproducibility, and features with CCCs ≥ 0.7 were considered reproducible. A coefficient of variation (CV) below 15% was considered low.

Results

Only a limited number of radiomics features had high CCC (T1: 6/96 ECV 0/96) or a low CV (T1: 32/96, ECV:30/96) in the between-session analysis. The inter-reader evaluation showed that the effect of the delineation on the results was limited. Features that were most robust in the between-session analysis were ‘first order (total)energy’ for T1 maps and ‘glcm_Autocorrelation’ for ECV maps (table 1). These results in young healthy subjects confirm previous test-retest reports [9-10]. Features with low CCC levels or high CV may however still be useful when discriminating between patient with myocardial diseases if the difference is larger than the confidence interval assessed via this reproducibility analysis.

Conclusion

In these healthy subjects, a strong variability in reproducibility of radiomics features of T1 and ECV mapping can be noted. Nonetheless, these variability measures are informative to determine features that are likely most robust when discriminating between health and disease and can be used as a benchmark towards radiomics AI-based diagnostic approaches. Top ranked features for either T1 or ECV

Reliability of MR Imaging-Based Posterior Fossa and Brain Stem Measurements in Open Spinal Dysraphism in the Era of Fetal Surgery

BACKGROUND AND PURPOSE

Fetal MR imaging is part of the comprehensive prenatal assessment of fetuses with open spinal dysraphism. We aimed to assess the reliability of brain stem and posterior fossa measurements; use the reliable measurements to characterize fetuses with open spinal dysraphism versus what can be observed in healthy age-matched controls; and document changes in those within 1 week after prenatal repair.

MATERIALS AND METHODS

Retrospective evaluation of 349 MR imaging examinations took place, including 274 in controls and 52 in fetuses with open spinal dysraphism, of whom 23 underwent prenatal repair and had additional early postoperative MR images. We evaluated measurements of the brain stem and the posterior fossa and the ventricular width in all populations for their reliability and differences between the groups.

RESULTS

The transverse cerebellar diameter, cerebellar herniation level, clivus-supraocciput angle, transverse diameter of the posterior fossa, posterior fossa area, and ventricular width showed an acceptable intra- and interobserver reliability (intraclass correlation coefficient > 0.5). In fetuses with open spinal dysraphism, these measurements were significantly different from those of healthy fetuses (all with P < .0001). Furthermore, they also changed significantly (P value range = .01 to < .0001) within 1 week after the fetal operation with an evolution toward normal, most evident for the clivus-supraocciput angle (65.9 ± 12.5°; 76.6 ± 10.9; P < .0001) and cerebellar herniation level (-9.9 ± 4.2 mm; -0.7 ± 5.2; P < .0001).

CONCLUSIONS

In fetuses with open spinal dysraphism, brain stem measurements varied substantially between observers. However, measurements characterizing the posterior fossa could be reliably assessed and were significantly different from normal. Following a fetal operation, these deviations from normal values changed significantly within 1 week.

CT density measurement and H:H ratio are useful in diagnosing acute cerebral venous sinus thrombosis

BACKGROUND AND PURPOSE

Brain CT is widely used to exclude or confirm acute cerebral venous sinus thrombosis. The purpose of this study was to assess the value of attenuation measurement and the H:H ratio on unenhanced brain CT scans in the diagnosis of acute cerebral venous sinus thrombosis.

MATERIALS AND METHODS

This retrospective study evaluated 20 patients with acute cerebral venous sinus thrombosis and 20 age- and sex-matched control participants without thrombosis. Three experienced observers independently evaluated the unenhanced brain CT scan for the presence of cerebral venous sinus thrombosis and measured the attenuation in the dural sinuses. Interreader differences were examined, as well as densities and H:H ratio between patients with acute cerebral venous sinus thrombosis and control participants.

RESULTS

A significant difference in the average sinus attenuation was found between patients with acute cerebral venous sinus thrombosis (73.9 ± 9.2 HU) and the control group (52.8 ± 6.7 HU; P < .0001). A similar difference was found for the H:H ratio (1.91 ± 0.32 vs 1.33 ± 0.12 in patients with and without cerebral venous sinus thrombosis, respectively; P < .0001). Optimal thresholds of 62 HU and 1.52 lead to accuracies of 95% for average sinus attenuation and 97.5% for the H:H ratio, respectively.

CONCLUSIONS

Hyperattenuation and the H:H ratio in the dural sinuses on unenhanced brain CT scans have a high accuracy in the detection of acute cerebral venous sinus thrombosis.

Diffusion-weighted MRI in lungs of normal fetuses and those with congenital diaphragmatic hernia

OBJECTIVE

To prospectively determine apparent diffusion coefficient (ADC) values of normally developing fetal lungs over gestation, as obtained by diffusion-weighted (DW) magnetic resonance imaging (MRI) and to investigate its potential application in fetuses with congenital diaphragmatic hernia (CDH).

METHODS

Informed consent was obtained for this cross-sectional study of 93 fetuses with normal lungs and 14 with isolated left-sided CDH, assessed between 18 and 40 weeks of gestation. MRI delineation of left and right lungs was performed on the native DW image, b0, and three values of ADC, corresponding to the overall value (ADC(avg)), and values for low and high values of b (ADC(low) and ADC(high), respectively) were calculated. Regression analysis was used to assess the relationship between gestational age and b0-values as well as calculated ADC values. The b0 and ADC values of normal and CDH fetuses were compared with normal ranges using the Mann-Whitney U-test.

RESULTS

In fetuses with normal lungs, there was a negative correlation between gestational age and b0 values as well as with ADC(high), a positive correlation with ADC(low) but no correlation with ADC(avg). When measurable, ADC(high) values were lower in CDH as compared to fetuses with normal lungs and ADC(low) values were higher. ADC(low) was unrelated to lung volume.

CONCLUSIONS

There is a significant relationship between ADC(low) and ADC(high) values and gestational age in normal fetal lungs. This relationship is most probably explained by developmental changes during the last three stages of lung development, which involve intense peripheral growth of airways and vessels as well as maturation. In CDH, measurement of ADC(low) might be useful as a predictor of postnatal outcome that is independent of lung volume.

Can apparent diffusion coefficient discriminate ischemic from nonischemic livers? A pilot experimental study

PURPOSE

Using magnetic resonance imaging, the apparent diffusion coefficient (ADC) is an indicator to assess cerebral ischemia. The aim of this porcine study was to evaluate whether ADC assessed hepatic ischemia during ex vivo hypothermic machine perfusion (HMP) as well as in vivo.

METHODS

Ex vivo: ADC of normal versus warm ischemic (WI) livers was assessed during HMP and subsequent rewarming to mimic ischemia-reperfusion injury. As the preservation solution, we used either an acellular solution or diluted blood. WI was induced in the left lobe or in the whole liver and compared 2-hour WI and non-WI. In vivo: One liver was scanned with the left lobe vessels occluded for 2-hour WI and subsequently for 3 hour reperfusion to compare with the right lobe without WI. Aspartate aminotransferase (AST) in the perfusate and morphology were used as surrogates of WI.

RESULTS

In all WI livers, AST reached high levels and histology showed severe injury. Ex vivo ADC during acellular perfusion showed negligible differences between the livers with versus without WI, namely, 0.75 x 10(-3) or 0.88 x 10(-3) mm(2)/s during HMP. Ex vivo ADC using sanguineous perfusion showed 1.11 x 10(-3) or 0.83 x 10(-3) mm(2)/s during HMP in regions with versus without WI, respectively, a difference that remained stable during the whole experiment. ADC in vivo decreased from the physiological level of 1.07 x 10(-3) mm(2)/s to 0.75 x 10(-3) mm(2)/s in the first 30 minutes of WI, whereas ADC in the non-WI liver remained constant.

CONCLUSION

ADC in vivo decreased during hepatic ischemia, as previously seen in cerebral ischemia. However, the effect of WI on ADC was less clear during ex vivo HMP.

Perfusion-and diffusion-weighted imaging of hepatocellular carcinoma

Improved surgical and non-surgical treatment for hepatocellular carcinoma in cirrhosis requires an adaptation of diagnostic strategies towards the characterization and follow-up of treatment response. Except of morphology, existing radiological techniques provide little information concerning tissue characterization, hampering the differentiation of small cirrhotic nodules and the assessment of treatment induced necrosis. The tumoral vasculature and cellular microstructure offer attractive diagnostic targets for functional imaging techniques. The aim of this paper is to discuss the potential applications of perfusion- and diffusion-imaging in the diagnosis and treatment follow-up of hepatocellular carcinoma.

A diffusion-weighted template for gestational age-related apparent diffusion coefficient values in the developing fetal brain

OBJECTIVE

To determine the pattern of apparent diffusion coefficient (ADC) values in the normal fetal brain obtained with diffusion-weighted images (DWI) on magnetic resonance imaging (MRI) as a template for normal brain development throughout gestation.

METHODS

This was a prospective study of 46 fetuses without suspicion of brain pathology undergoing a total of 66 ultrasound examinations between 17 and 37 weeks of gestation. At T2-weighted MRI, four left and four right brain regions were delineated on transverse slices of the native DWI using a b-value of 0 s/mm2 (b0 images). We examined native b-value images and calculated ADC(avg), ADC(low) and ADC(high) in the basal ganglia, cerebellar hemisphere, frontal parenchyma and occipital parenchyma. Linear regression analysis was used to assess the relationship between gestational age and b0 values as well as the calculated ADC values.

RESULTS

Delineations were successful in all fetuses for all regions except for the cerebellar hemispheres in four fetuses. There was a negative correlation between gestational age and b0 values in all examined anatomical regions (P<0.002). For ADC(avg), there were no significant changes in the basal ganglia with increasing gestational age, a positive correlation in the frontal (P<0.0001) and occipital (P=0.03) parenchyma and a negative correlation in the cerebellar hemispheres (P=0.01). For ADC(low), there was a negative correlation between gestational age and the cerebellum (P=0.0002) and basal ganglia (P=0.047), but no correlation for the frontal or occipital parenchyma. For ADC(high), there was a positive correlation with gestational age for the frontal parenchyma (P=0.004), occipital parenchyma (P=0.02) and basal ganglia (P=0.03) but there was no correlation for the cerebellum.

CONCLUSIONS

DWI b0 values decreased in the left and right basal ganglia, cerebellar hemisphere, frontal parenchyma and occipital parenchyma between 17 and 37 weeks of gestation and ADC(avg) values increased in two out of four cerebral regions. It remains to be determined to what extent these observations differ in fetuses with suspicion of brain anomalies and whether such measurements will be useful and more predictive of outcome compared with standard MRI sequences.

Magnetization transfer analysis of cartilage repair tissue: a preliminary study

PURPOSE

To evaluate the magnetization transfer ratio (MTR) after two different cartilage repair procedures, and to compare these data with the MTR of normal cartilage.

DESIGN AND PATIENTS

Twenty-seven patients with a proven cartilage defect were recruited: 13 were treated with autologous chondrocyte implantation (ACI) and 14 were treated with the microfracture technique (MFR). All patients underwent MRI examinations with MT-sequences before the surgical treatment, after 12 months (26 patients) and after 24 months (11 patients). Eleven patients received a complete follow-up study at all three time points (five of the ACI group and six of the MFR group). All images were transferred to a workstation to calculate MTR images. For every MT image set, different ROIs were delineated by two radiologists. Means were calculated per ROI type in the different time frames and in both groups of cartilage repair. The data were analyzed with unpaired t- and ANOVA tests, and by calculating Pearson's correlation coefficient.

RESULTS

No significant differences were found in the MTR of fatty bone marrow, muscle and normal cartilage in the different time frames. There was a significant but small difference between the MTR of normal cartilage and the cartilage repair area after 12 months for both procedures. After 24 months, the MTR of ACI repaired cartilage (0.31+/-0.07) was not significantly different from normal cartilage MTR (0.34+/-0.05). The MTR of MFR repaired cartilage (0.28+/-0.02), still showed a significant difference from normal cartilage.

CONCLUSION

The differences between damaged and repaired cartilage MTR are too small to enable MT-imaging to be a useful tool for postoperative follow-up of cartilage repair procedures. There is, however, an evolution towards normal MTR-values in the cartilage repair tissue (especially after ACI repair).