Multi-organ Radiomics-Based Prediction of Future Remnant Liver Hypertrophy Following Portal Vein Embolization

BACKGROUND

Portal vein embolization (PVE) is used to induce remnant liver hypertrophy prior to major hepatectomy. The purpose of this study was to evaluate the predictive value of baseline computed tomography (CT) data for future remnant liver (FRL) hypertrophy after PVE.

METHODS

In this retrospective study, all consecutive patients undergoing right-sided PVE with or without hepatic vein embolization between 2018 and 2021 were included. CT volumetry was performed before and after PVE to assess standardized FRL volume (sFRLV). Radiomic features were extracted from baseline CT after segmenting liver (without tumor), spleen and bone marrow. For selecting features that allow classification of response (hypertrophy ≥ 1.33), a stepwise dimension reduction was performed. Logistic regression models were fitted and selected features were tested for their predictive value. Decision curve analysis was performed on the test dataset.

RESULTS

A total of 53 patients with liver tumor were included in this study. sFRLV increased significantly after PVE, with a mean hypertrophy of FRL of 1.5 ± 0.3-fold. sFRLV hypertrophy ≥ 1.33 was reached in 35 (66%) patients. Three independent radiomic features, i.e. liver-, spleen- and bone marrow-associated, differentiated well between responders and non-responders. A logistic regression model revealed the highest accuracy (area under the curve 0.875) for the prediction of response, with sensitivity of 1.0 and specificity of 0.5. Decision curve analysis revealed a positive net benefit when applying the model.

CONCLUSIONS

This proof-of-concept study provides first evidence of a potential predictive value of baseline multi-organ radiomics CT data for FRL hypertrophy after PVE.

Impact of postoperative baseline MRI on diagnostic confidence and performance in detecting local recurrence of soft-tissue sarcoma of the limb

OBJECTIVE

To evaluate the impact of a postoperative baseline (PB) MRI on diagnostic confidence and performance in detecting local recurrence (LR) of soft-tissue sarcoma (STS) of the limb.

MATERIALS AND METHODS

A total of 72 patients (8 with LR, 64 without LR) with primary STS of the limb were included. Routine follow-up MRI (1.5 T) at 6 and approximately 36 months (meanLR: 39.7 months; meanno LR: 34.9 months) after multimodal therapy or at time of LR were assessed by three independent readers using a 5-point Likert scale. Furthermore, the following imaging parameters were evaluated: presence of a mass, signal characteristics at T2- and T1-weighted imaging, contrast enhancement (CE), and in some of the cases signal intensity on the apparent diffusion coefficient (ADC). U-test, McNemar test, and ROC-analysis were applied. Interobserver reliability was calculated using Fleiss kappa statistics. A p value of 0.05 was considered statistically significant.

RESULTS

The presence of a PB MRI significantly improved diagnostic confidence in detecting LR of STS (p < 0.001) and slightly increased specificity (mean specificity without PE 74.1% and with presence of PB MRI 81.2%); however, not to a significant level. The presence of a mass showed highest diagnostic performance and highest interreader agreement (AUC [%]; κ: 73.1-83.6; 0.34) followed by T2-hyperintensity (50.8-66.7; 0.08), CE (52.4-62.5; 0.13), and T1-hypointensity (54.7-77.3; 0.23). ADC showed an AUC of 65.6-96.6% and a κ of 0.55.

CONCLUSION

The presence of a PB MRI increases diagnostic confidence in detecting LR of STS of the limb.

Artifact characterization of Nitinol needles in magnetic resonance imaging-guided musculoskeletal interventions at 3.0 tesla: a phantom study

PURPOSE

To characterize the artifacts of an 18-gauge coaxial nickel-titanium needle using a balanced steady-state free precession sequence in magnetic resonance imaging-guided interventions at 3.0 tesla.

METHODS

The influence of flip angle (FA), bandwidth, matrix, slice thickness (ST), and read-out direction on needle artifact behavior was investigated for different intervention angles (IA). Artifact diameters were rated at predefined positions. Subgroup differences were assessed using Bonferroni-corrected non-parametric tests and correlations between continuous variables were expressed using the Bravais-Pearson coefficient. Interrater reliability was quantified using intraclass correlation coefficients (ICCs), and a contrast-enhanced target lesion to non-enhanced muscle tissue contrast ratio was quantified.

RESULTS

The artifact diameters decreased with an increase in FA for all IAs (P < 0.001) and with an increase in ST for IAs of 45°-90° (all P < 0.05). Tip artifacts occurred at low IAs (0°-45°) and gradually increased in size with a decrease in IA (P = 0.022). The interrater reliability was high (ICC: 0.994-0.999). The contrast-enhanced target lesion to non-enhanced muscle tissue contrast ratio presented positive correlations with increasing FAs and matrices (P < 0.001; P = 0.003) and a negative correlation with increasing STs (P = 0.007).

CONCLUSION

To minimize needle artifacts, it is recommended to use FAs of 40°-60°, a ST of >7 mm, and, if possible, an IA of 45°-60°. The visibility of the target lesion and the needle's artifact behavior must be weighed up against each other when choosing the ST, while higher FAs (40°-60°) and matrices (224 × 224/256 × 256) are associated with low artifacts and sufficient lesion visibility.

Optimized visualization of focal liver lesions and vascular structures in real-time T1-weighted gradient echo sequences for magnetic resonance-guided liver procedures

PURPOSE

This study aimed to determine the optimal sequence parameters of a real-time T1-weighted (T1w) gradient echo (GRE) sequence for magnetic resonance (MR)-guided liver interventions.

METHODS

We included 94 patients who underwent diagnostic liver MR imaging (MRI) and acquired additional real-time T1w GRE sequences with a closed 1.5-T MRI scanner 20 min after a liver-specific contrast agent was injected. In four measurement series, one of the following four sequence parameters was changed, and repeated scans with different values for this parameter were acquired: flip angle (FA) (10-90°), repetition time (TR) (5.47-8.58 ms), bandwidth (BW) (300-700 Hz/pixel), and matrix (96 × 96-256 × 256). Two readers rated the visualizations of the target and risk structures (7-point Likert scale) and the extent of artifacts (6-point Likert scale); they also quantified the lesion-liver contrast ratio, the lesion-liver contrast-to-noise ratio (CNR), and the liver signal-to-noise ratio (SNR). Substratification analyses were performed for differences in overall visual and quantitative assessments depending on the lesion size, type, and the presence of cirrhosis.

RESULTS

For the utilized FAs and matrix sizes, significant differences were found in the visual assessments of the conspicuity of target lesions, risk structures, and the extent of artifacts as well as in the quantitative assessments of lesion-liver contrast ratios and liver SNRs (all P < 0.001). No differences were observed for modified TR and BW. Significantly increased conspicuity of the target and vascular structures was observed for both higher FAs and matrix sizes, while the ghosting artifacts increased and decreased, respectively. For primary liver tumors compared with metastatic lesions, and for cirrhotic livers compared with normal liver parenchyma, significantly decreased conspicuity of the target lesions (P = 0.005, P = 0.005), lesion-liver CNRs (P = 0.005, P = 0.032), and lesion-liver contrast ratios (P = 0.015, P = 0.032) were found. All results showed no significant correlation with lesion size.

CONCLUSION

We recommend an FA of 30°-45° and a matrix size of 128 × 128-192 × 192 for MR-guided liver interventions with real-time T1w sequences to provide a balance between good visualizations of target and risk structures, high signal intensities, and low ghosting artifacts. The visualization of the target lesion may vary due to clinical conditions, such as lesion type or associated chronic liver disease.

Artifact reduction of coaxial needles in magnetic resonance imaging-guided abdominal interventions at 1.5 T: a phantom study

Needle artifacts pose a major limitation for MRI-guided interventions, as they impact the visually perceived needle size and needle-to-target-distance. The objective of this agar liver phantom study was to establish an experimental basis to understand and reduce needle artifact formation during MRI-guided abdominal interventions. Using a vendor-specific prototype fluoroscopic T1-weighted gradient echo sequence with real-time multiplanar acquisition at 1.5 T, the influence of 6 parameters (flip angle, bandwidth, matrix, slice thickness, read-out direction, intervention angle relative to B₀) on artifact formation of 4 different coaxial MR-compatible coaxial needles (Nitinol, 16G–22G) was investigated. As one parameter was modified, the others remained constant. For each individual parameter variation, 2 independent and blinded readers rated artifact diameters at 2 predefined positions (15 mm distance from the perceived needle tip and at 50% of the needle length). Differences between the experimental subgroups were assessed by Bonferroni-corrected non-parametric tests. Correlations between continuous variables were expressed by the Bravais–Pearson coefficient and interrater reliability was quantified using the intraclass classification coefficient. Needle artifact size increased gradually with increasing flip angles (p = 0.002) as well as increasing intervention angles (p < 0.001). Artifact diameters differed significantly between the chosen matrix sizes (p = 0.002) while modifying bandwidth, readout direction, and slice thickness showed no significant differences. Interrater reliability was high (intraclass correlation coefficient 0.776–0.910). To minimize needle artifacts in MRI-guided abdominal interventions while maintaining optimal visibility of the coaxial needle, we suggest medium-range flip angles and low intervention angles relative to B₀.

Mosaic RASopathy due to KRAS variant G12D with segmental overgrowth and associated peripheral vascular malformations

Oncogenic RAS variants lead to constitutive overactivation and increased signal transduction into downstream pathways. They are found as somatic driver events in various types of human cancer. In a somatic mosaic status, the same RAS variants have been associated with a wide spectrum of focal or segmental tissue dysplasia and overgrowth including various types of congenital nevi, vascular malformations, and other changes (mosaic RASopathies). We present a 3-year-old male patient with segmental overgrowth of the subcutaneous fatty tissue of the right lower extremity with colocalized arteriovenous and capillary malformations and dysplastic draining veins in combination with talipes equinovarus of the right foot. In tissue biopsies of the affected extremity, we identified a mosaic KRAS variant, c.35G>A (p.Gly12Asp), while this variant was absent in the DNA extracted from a biopsy of the normal extremity. This report provides further evidence for the wide clinical and phenotypic variability associated with mosaic KRAS variants. The described pattern confirms that the combination of segmental overgrowth and vascular anomalies in the form of arteriovenous and capillary malformations is a possible manifestation of a mosaic RASopathy. The accurate genetic diagnosis is crucial for molecular-targeted therapy, which might be a future therapeutic target for mosaic RASopathies.