Percutaneous Microwave Ablation for Treatment of Retroperitoneal Tumors

Purpose To determine if microwave ablation (MWA) of retroperitoneal tumors can safely provide high rates of local tumor control. Materials and Methods This retrospective study included 19 patients (median age, 65 years [range = 46-78 years]; 13 [68.4%] men and six [31.6%] women) with 29 retroperitoneal tumors treated over 22 MWA procedures. Hydrodissection (0.9% saline with 2% iohexol) was injected in 17 of 22 (77.3%) procedures to protect nontarget anatomy. The primary outcomes evaluated were local tumor progression (LTP) and complication rates. Oncologic outcomes, including overall survival (OS), progression-free survival (PFS), and treatment-free interval (TFI), were examined as secondary outcome measures. Results Median follow-up was 18 months (range = 0.5-113). Hydrodissection was successful in displacing nontarget anatomy in 16 of 17 (94.1%) procedures. The LTP rate was 3.4% (one of 29; 95% CI: 0.1, 17.8) per tumor and 5.3% (one of 19; 95% CI: 0.1, 26.0) per patient. The overall complication rate per patient was 15.8% (three of 19), including two minor complications and one major complication. The OS rate at 1, 2, and 3 years was 81.8%, 81.8%, and 72.7%, respectively, with a median OS estimated at greater than 7 years. There was no evidence of a difference in OS (P = .34) and PFS (P = .56) between patients with renal cell carcinoma (six of 19 [31.6%]) versus other tumors (13 of 19 [68.4%]) and patients treated with no evidence of disease (15 of 22 [68.2%]) versus patients with residual tumors (seven of 22 [31.8%]). Median TFI was 18 months (range = 0.5-108). Conclusion Treatment of retroperitoneal tumors with MWA combined with hydrodissection provided high rates of local control, prolonged systemic therapy-free intervals, and few serious complications. Keywords: Ablation Techniques (ie, Radiofrequency, Thermal, Chemical), Retroperitoneum, Microwave Ablation, Hydrodissection © RSNA, 2024.

Imaging Genomics and Multiomics: A Guide for Beginners Starting Radiomics-Based Research

Radiomics uses advanced mathematical analysis of pixel-level information from radiologic images to extract existing information in traditional imaging algorithms. It is intended to find imaging biomarkers related to the genomics of tumors or disease patterns that improve medical care by advanced detection of tumor response patterns in tumors and to assess prognosis. Radiomics expands the paradigm of medical imaging to help with diagnosis, management of diseases and prognostication, leveraging image features by extracting information that can be used as imaging biomarkers to predict prognosis and response to treatment. Radiogenomics is an emerging area in radiomics that investigates the association between imaging characteristics and gene expression profiles. There are an increasing number of research publications using different radiomics approaches without a clear consensus on which method works best. We aim to describe the workflow of radiomics along with a guide of what to expect when starting a radiomics-based research project.

Using 18F-DCFPyL Prostate-Specific Membrane Antigen-Directed Positron Emission Tomography/Magnetic Resonance Imaging to Define Intraprostatic Boosts for Prostate Stereotactic Body Radiation Therapy

Purpose

The recently reported FLAME trial demonstrated a biochemical disease-free survival benefit to using a focal intraprostatic boost to multiparametric magnetic resonance imaging (mpMRI)-identified lesions in men with localized prostate cancer treated with definitive radiation therapy. Prostate-specific membrane antigen (PSMA)-directed positron emission tomography (PET) may identify additional areas of disease. In this work, we investigated using both PSMA PET and mpMRI in planning focal intraprostatic boosts using stereotactic body radiation therapy (SBRT).

Methods and Materials

We evaluated a cohort of patients (n = 13) with localized prostate cancer who were imaged with 2-(3-(1-carboxy-5-[(6-[18F]fluoro-pyridine-2-carbonyl)-amino]-pentyl)-ureido)-pentanedioic acid (¹⁸F-DCFPyL) PET/MRI on a prospective imaging trial before undergoing definitive therapy. The number of lesions concordant (overlapping) and discordant (no overlap) on PET and MRI was assessed. Overlap between concordant lesions was evaluated using the Dice and Jaccard similarity coefficients. Prostate SBRT plans were created fusing the PET/MRI imaging to computed tomography scans acquired the same day. Plans were created using only MRI-identified lesions, only PET-identified lesions, and the combined PET/MRI lesions. Coverage of the intraprostatic lesions and doses to the rectum and urethra were assessed for each of these plans.

Results

The majority of lesions (21/39, 53.8%) were discordant between MRI and PET, with more lesions seen by PET alone (12) than MRI alone (9). Of lesions that were concordant between PET and MRI, there were still areas that did not overlap between scans (average Dice coefficient, 0.34). Prostate SBRT planning using all lesions to define a focal intraprostatic boost provided the best coverage of all lesions without compromising constraints on the rectum and urethra.

Conclusions

Using both mpMRI and PSMA-directed PET may better identify all areas of gross disease within the prostate. Using both imaging modalities could improve the planning of focal intraprostatic boosts.

Assessment of 18F-DCFPyL PSMA PET/CT and PET/MR quantitative parameters for reference standard organs: Inter-reader, inter-modality, and inter-patient variability

Prostate specific membrane antigen (PSMA)-based radiotracers have shown promise for prostate cancer assessment. Evaluation of quantitative variability and establishment of reference standards are important for optimal clinical and research utility. This work evaluates the variability of PSMA-based [18F]DCFPyL (PyL) PET quantitative reference standards. Consecutive eligible patients with biochemically recurrent prostate cancer were recruited for study participation from August 2016-October 2017. After PyL tracer injection, whole body PET/CT (wbPET/CT) was obtained with subsequent whole body PET/MR (wbPET/MR). Two readers independently created regions of interest (ROIs) including a 40% standardized uptake value (SUV) threshold ROI of the whole right parotid gland and separate spherical ROIs in the superior, mid, and inferior gland. Additional liver (right lobe) and blood pool spherical ROIs were defined. Bland-Altman analysis, including limits of agreement (LOA), as well as interquartile range (IQR) and coefficient of variance (CoV) was used. Twelve patients with prostate cancer were recruited (mean age, 61.8 yrs; range 54-72 years). One patient did not have wbPET/MR and was excluded. There was minimal inter-reader SUVmean variability (bias±LOA) for blood pool (-0.13±0.42; 0.01±0.41), liver (-0.55±0.82; -0.22±1.3), or whole parotid gland (-0.05±0.31; 0.08±0.24) for wbPET/CT and wbPET/MR, respectively. Greater inter-reader variability for the 1-cm parotid gland ROIs was present, for both wbPET/CT and wbPET/MR. Comparing wbPET/CT to the subsequently acquired wbPET/MR, blood pool had a slight decrease in SUVmean. The liver as well as parotid gland showed a slight increase in activity although the absolute bias only ranged from 0.45-1.28. The magnitude of inter-subject variability was higher for the parotid gland regardless of modality or reader. In conclusion, liver, blood pool, and whole parotid gland quantitation show promise as reliable reference normal organs for clinical/research PET applications. Variability with 1-cm parotid ROIs may limit its use.

Contrast-enhanced CT immediately following percutaneous microwave ablation of cT1a renal cell carcinoma: Optimizing cancer outcomes

OBJECTIVE

To evaluate the effect of intra-procedural contrast-enhanced CT (CECT) and same-session repeat ablation (SSRA) on primary efficacy, the complete eradication of tumor after the first ablation session as confirmed on first imaging follow-up, of clinically localized T1a (cT1a) renal cell carcinoma (RCC).

METHODS

398 consecutive patients with cT1a RCC were treated with cryoablation between 10/2003 and 12/2017, radiofrequency (RFA) or microwave ablation (MWA) between 1/2010 and 12/2017. SSRA was performed for residual tumor identified on intra-procedural CECT. Kruskal-Wallis and Pearson's chi-squared tests were performed to assess differences in continuous and categorical variables, respectively. Multivariate linear regression was used to determine predictors for primary efficacy and decline in estimated glomerular filtration rate.

RESULTS

347 consecutive patients (231 M, mean age 67.5 ± 9.1 years) were included. Median tumor diameter was smaller [2.5 vs 2.7 vs 2.6 (p = 0.03)] and RENAL Nephrometry Score (NS) was lower [6 vs 7 vs 7 (p = 0.009] for MWA compared to the RFA and cryoablation cohorts, respectively. Primary efficacy was higher in the MWA cohort [99.4% (170/171)] compared to the RFA [91.4% (85/93)] and cryoablation [92.8% (77/83)] cohorts (p = 0.001). Microwave ablation and SSRA was associated with higher primary efficacy on multivariate linear regression (p = 0.01-0.03).

CONCLUSION

MWA augmented by SSRA, when residual tumor is identified on intra-procedural CECT, may improve primary efficacy for cT1a RCC.

Advanced CT techniques for hepatic microwave ablation zone monitoring and follow-up

PURPOSE

To evaluate utility of advanced CT techniques including HighlY constrained back-projection and dual-energy CT for intra- and post-procedure hepatic microwave ablation zone monitoring.

METHODS

8 hepatic microwave ablations were performed in 4 adult swine (5 min/65 W). Low-dose routine CECT and dual-energy CT images were obtained every 1 min during ablation. Images were reconstructed ± HYPR. Image quality and dose metrics were collected. 21 MWA were performed in 4 adult swine. Immediate post-procedure CECT was performed in the arterial, portal venous, and delayed phases using both routine and DECT imaging with full-dose weight-based IV contrast dosing. An additional 16 MWA were subsequently performed in 2 adult swine. Immediate post-procedure CT was performed with half-dose IV contrast using routine and DECT. 12 patients (10 M/2F, mean age 62.4 yrs) with 14 hepatic tumors (4 HCC, 10 metastatic lesions) treated with MWA were prospectively imaged with DECT 1 month post-procedure. 120 kV equivalent images were compared to DECT [51 keV, iodine material density]. Image quality and dose metrics were collected.

RESULTS

Gas created during MWA led to high CNR in all intraprocedural CT datasets. Optimal CNRs were noted at 4 min with CNR 6.7, 15.5,15.9, and 21.5 on LD-CECT, LD-CECT + HYPR, DECT, and DECT + HYPR, respectively (p < 0.001). Image quality scores at 4 min were 1.8, 2.8, 2.4, and 3, respectively (p < 0.001). Mean radiation dose (CTDI_vol) was eightfold higher for the DECT series. For swine, post-procedural DECT images (IMD/51 keV) showed improved CNR compared to routine CT at all time points with full and with reduced dose contrast (CNR 4.6, 3.2, and 1.5, respectively, at half-contrast dose, p < 0.001). For human subjects, the 51 keV and IMD images showed higher CNRs (5.8, 4.8 vs 4.0, p < 0.001) and SNRs (3.7, 5.9 vs 2.8). Ablation zone sharpness was improved with DECT (routine 3.0 ± 0.7, DECT 3.5 ± 0.5). Diagnostic confidence was higher with DECT (routine 2.3 ± 0.9, DECT 2.6 ± 0.8). Mean DLP for DECT was 905.7 ± 606 mGy-cm, CTDI_vol 37.5 ± 21.2 mGy, and effective dose 13.6 ± 9.1 mSv, slightly higher than conventional CT series.

CONCLUSION

Advanced CT techniques can improve CT image quality in peri-procedural hepatic microwave ablation zone evaluation.

Efficacy of percutaneous image-guided biopsy for diagnosis of intrahepatic cholangiocarcinoma

PURPOSE

To evaluate the efficacy of percutaneous biopsy for diagnosing intrahepatic cholangiocarcinoma (IHCCA).

METHODS

Retrospective review of biopsy and pathology databases from 2006 to 2019 yielded 112 patients (54F/58 M; mean age, 62.9 years; 27 cirrhotic) with IHCCA who underwent percutaneous biopsy. Data regarding the lesion, biopsy procedure technique, and diagnostic yield were collected. If biopsy was non-diagnostic or discordant with imaging, details of repeat biopsy or resection/explant were gathered. A control group of 100 consecutive patients (56F/44 M; mean age, 63 years, 5 cirrhotic) with focal liver lesions > 1 cm was similarly assessed.

RESULTS

Mean IHCCA lesion size was 6.1 ± 3.6 cm, with dominant lesion sampled in 78% (vs. satellite in 22%). 95% (n = 106) were US guided and 96% were core biopsies (n = 108), typically 18G (n = 102, 91%), median 2 passes. 18 patients (16%) had discordant/ambiguous pathology results requiring repeat biopsy, with two patients requiring 3-4 total attempts. A 4.4% minor complication rate was seen. Mean time from initial biopsy to final diagnosis was 60 ± 120 days. Control group had mean lesion size of 2.9 ± 2.5 cm and showed a non-diagnostic rate of 3.3%, both significantly lower than that seen with CCA, with average time to diagnosis of 21 ± 28.8 days (p = 0.002, p = 0.001).

CONCLUSION

IHCCA is associated with lower diagnostic yield at initial percutaneous biopsy, despite larger target lesion size. If a suspicious lesion yields a biopsy result discordant with imaging, the radiologist should recommend prompt repeat biopsy to prevent delay in diagnosis.

Combined mpMRI/US fusion targeted and concurrent standard biopsies in the detection of prostate cancer: a retrospective study

In this retrospective study we compared the PCa detection rates between combined (combined MRI/US fusion targeted biopsy with concurrent standard biopsy) and standard systemic, combined and targeted (component), and targeted (component) and concurrent standard (component) biopsies.

DESIGN

Two cohorts, totaling 735 cases, were selected from the University of Wisconsin Pathology archive. 390 cases (cohort 1) were combined biopsies from 2017-2020 and 345 cases (cohort 2) were part of the standard US-guided systematic biopsies from the same period. PCa was stratified into three categories: low, intermediate, and high risks.

RESULTS

We found that combined biopsy was significantly better than the standard biopsy in detection of PCa (65.4% vs. 51.6%, P<0.01) and intermediate-risk PCa (18.7% vs. 10.4%, P=0.05) but only slightly better at detecting high-risk PCa (26.7% vs. 23.5%, P=0.32). Further examining the biopsy results in cohort 1, we found that combined biopsy was superior to targeted biopsy (65.4% vs. 56.9%, P=0.02) or concurrent standard biopsy (65.4% vs. 52.1%, P=0.0002) in PCa detection. Combined biopsy detected significantly more high-risk PCa than concurrent standard biopsy (26.7% vs. 17.4, P=0.002), but the difference in detecting high-risk PCa between combined and targeted biopsies was not significant (26.7% vs. 22.1%, P=0.133). Similarly, the differences in detecting PCa and high-risk PCa between targeted and concurrent standard biopsies were not significant (56.9% vs. 52.1%, P=0.172 and 22.1% vs. 17.4, P=0.133, respectively). Both targeted and concurrent standard biopsies missed PCa of each risk level.

CONCLUSION

Combined MRI/US fusion targeted plus standard prostate biopsy is a superior technique for the detection of PCa and clinically significant PCa.

Microwave ablation for colorectal cancer metastasis to the liver: a single-center retrospective analysis

Background

The purpose of this study is to evaluate the safety and intermediate-term efficacy of percutaneous microwave (MW) ablation for the treatment of colorectal liver metastases (CRLM) at a single institution.

Methods

A retrospective review was performed of all CRLM treated with MW ablation from 3/2011 to 7/2020 (102 tumors; 72 procedures; 57 patients). Mean age was 60 years (range, 36-88) and mean tumor size was 1.8 cm (range, 0.5-5.0 cm). The patient population included 19 patients with extra-hepatic disease. Chemotherapy (pre- and/or post-ablation) was given in 98% of patients. Forty-five sessions were preceded by other focal CRLM treatments including resection, ablation, radiation, and radioembolization. Kaplan-Meier curves were used to estimate local tumor progression-free survival (LTPFS), disease-free survival (DFS), and overall survival (OS) and multivariate analysis (Cox Proportional Hazards model) was used to test predictors of OS.

Results

Technical success (complete ablation) was 100% and median follow-up was 42 months (range, 1-112). There was a 4% major complication rate and an overall complication rate of 8%. Local tumor progression (LTP) rate during the entire study period was 4/98 (4%), in which 2 were retreated with MW ablation for a secondary LTP-rate of 2%. LTP-free survival at 1, 3, and 5 years was 93%, 58%, and 39% and median LTP-free survival was 48 months. OS at 1, 3, and 5 years was 96%, 66%, 47% and median OS was 52 months. There were no statistically significant predictors of OS.

Conclusions

MW ablation of hepatic colorectal liver metastases appears safe with excellent local tumor control and prolonged survival compared to historical controls in selected patients. Further comparative studies with other local treatment strategies appear indicated.

Microwave Ablation of Renal Cell Carcinoma

Management options for small renal masses include active surveillance, partial nephrectomy, radical nephrectomy, and thermal ablation. For tumors typically ≤3 cm in size, thermal ablation is a good option for those desiring an alternative to surgery or active surveillance, especially in patients who are considered high surgical risk. We favor microwave ablation because of the more rapid heating, higher temperatures that overcome the heat sink effect of vessels, reproducible cell kill, and a highly visible ablation zone formed by water vapor that corresponds well to the zone of necrosis. For central tumors, we favor cryoablation because of the slower formation of the ablation zone and less likelihood of damage to the collecting system. With microwaves, it is important to monitor the ablation zone in real time (ultrasound is the best modality for this purpose), avoid direct punctures of the collecting system, and to place probes tangential to the collecting system to avoid burning open a persistent tract between the urothelium and extrarenal spaces or causing strictures. The surgical steps described in this video cover our use of high-frequency jet ventilation with general anesthesia to minimize organ motion, initial imaging and targeting, probe insertion, hydrodissection (a technique that enables displacement of adjacent structures), the ablation itself, and finally our dressing. Postoperative cares typically consist of observation with a same-day discharge or an overnight stay. Follow-up includes a magnetic resonance imaging abdomen with and without contrast, chest X-ray, and laboratories (basic metabolic panel, complete blood count, and C-reactive protein) 6 months postablation. Overall, percutaneous microwave ablation is an effective and safe treatment option for renal cell carcinoma in both T1a and T1b tumors in selected patients with multiple studies showing excellent oncologic outcomes when compared with partial and radical nephrectomy.

Differential Imaging of Liver Tumors before and after Microwave Ablation with Electrode Displacement Elastography

Liver cancer is a leading cause of cancer-related deaths; however, primary treatment options such as surgical resection and liver transplant may not be viable for many patients. Minimally invasive image-guided microwave ablation (MWA) provides a locally effective treatment option for these patients with an impact comparable to that of surgery for both cancer-specific and overall survival. MWA efficacy is correlated with accurate image guidance; however, conventional modalities such as B-mode ultrasound and computed tomography have limitations. Alternatively, ultrasound elastography has been used to demarcate post-ablation zones, yet has limitations for pre-ablation visualization because of variability in strain contrast between cancer types. This study attempted to characterize both pre-ablation tumors and post-ablation zones using electrode displacement elastography (EDE) for 13 patients with hepatocellular carcinoma or liver metastasis. Typically, MWA ablation margins of 0.5-1.0 cm are desired, which are strongly correlated with treatment efficacy. Our results revealed an average estimated ablation margin inner quartile range of 0.54-1.21 cm with a median value of 0.84 cm. These treatment margins lie within or above the targeted ablative margin, indicating the potential to use EDE for differentiating index tumors and ablated zones during clinical ablations. We also obtained a high correlation between corresponding segmented cross-sectional areas from contrast-enhanced computed tomography, the current clinical gold standard, when compared with EDE strain images, with r2 values of 0.97 and 0.98 for pre- and post-ablation regions.

Comprehensive non-invasive analysis of lower urinary tract anatomy using MRI

PURPOSE

Anatomic changes that coincide with aging including benign prostatic hyperplasia (BPH) and lower urinary tract symptoms (LUTS) negatively impact quality of life. Use of MRI with its exquisite soft tissue contrast, full field-of-view capabilities, and lack of radiation is uniquely suited for quantifying specific lower urinary tract features and providing comprehensive measurements such as total bladder wall volume (BWV), bladder wall thickness (BWT), and prostate volume (PV). We present a technique for generating 3D anatomical renderings from MRI to perform quantitative analysis of lower urinary tract anatomy.

METHODS

T2-weighted fast-spin echo MRI of the pelvis in 117 subjects (59F;58 M) aged 30-69 (49.5 ± 11.3) without known lower urinary tract symptoms was retrospectively segmented using Materialise software. Virtual 3D models were used to measure BWV, BWT, and PV.

RESULTS

BWV increased significantly between the 30-39 and 60-69 year age group in women (p = 0.01), but not men (p = 0.32). BWV was higher in men than women aged 30-39 and 40-49 (p = 0.02, 0.05, respectively) ,but not 50-59 or 60-69 (p = 0.18, 0.16, respectively). BWT was thicker in men than women across all age groups. Regional differences in BWT were observed both between men and women and between opposing bladder wall halves (anterior/posterior, dome/base, left/right) within each sex in the 50-59 and 60-69 year groups. PV increased from the 30-39 to 60-69 year groups (p = 0.05). BWT was higher in subjects with enlarged prostates (> 40cm³) (p = 0.05).

CONCLUSION

Virtual 3D MRI models of the lower urinary tract reliably quantify sex-specific and age-associated changes of the bladder wall and prostate.

Effect of iodinated contrast material on post-operative eGFR when administered during renal mass ablation

OBJECTIVE

To evaluate the effect of intravenous iodinated contrast on estimated glomerular filtration rate (eGFR) when administered immediately after thermal ablation of clinically localized T1a (cT1a) renal cell carcinoma (RCC).

METHODS

This HIPAA-compliant, dual-center retrospective study was performed under a waiver of informed consent. Three hundred forty-two consecutive patients with cT1a biopsy-proven RCC were treated with percutaneous ablation between January 2010 and December 2017. Immediate post-ablation contrast-enhanced CT was the routine standard of care at one institution (contrast group), but not the other (control group). One-month pre- and 6-month post-ablation eGFR were compared using the Wilcoxon signed-rank test or the Kruskal-Wallis test. Multivariate linear regression was used to determine the effect of contrast on eGFR. A 1:1 propensity score matching was performed for all patients with a logistic model using patient, tumor, and procedural covariates.

RESULTS

In total, 246 patients (158 M; median age 69 years, IQR 62-74) were included. Median tumor diameter (2.4 vs 2.5, p = 0.23) and RENAL nephrometry scores (6 vs 6, p = 0.92), surrogates for ablation zone size, were similar. Baseline kidney function was similar for the control and contrast groups, respectively (median eGFR: 70 vs 74 mL/min/1.73 m², p = 0.29). There was an expected mild decline in eGFR after ablation (control: 70 vs 60 mL/min/1.73 m², p < 0.001; contrast: 75 vs 71 mL/min/1.73 m², p = 0.001). Intravenous iodinated contrast was not associated with a decline in eGFR on multivariate linear regression (1.91, 95% CI - 3.43-7.24, p = 0.46) or 1:1 propensity score-matched model (- 0.33, 95% CI - 6.81-6.15, p = 0.92).

CONCLUSION

Intravenous iodinated contrast administered during ablation of cT1a RCC has no effect on eGFR.

KEY POINTS

• Intravenous iodinated contrast administered during thermal ablation of clinically localized T1a renal cell carcinoma has no effect on kidney function. • Thermal ablation of clinically localized T1a renal cell carcinoma results in a mild decline in kidney function. • A decline in kidney function is similar for radiofrequency and microwave ablation of clinically localized T1a renal cell carcinoma.

Long-Term Outcomes and Prognostic Factors in Kidney Transplant Recipients with Polycystic Kidney Disease

Background

Polycystic kidney disease (PKD) accounts for approximately 15% of kidney transplants, but long-term outcomes in patients with PKD who have received a kidney transplant are not well understood.

Methods

In primary recipients of kidney transplants at our center (1994-2014), we compared outcomes of underlying PKD (N=619) with other native diseases (non-PKD, N=4312). Potential factors influencing outcomes in PKD were evaluated using Cox proportional-hazards regression and a rigorous multivariable model.

Results

Patients with PKD were older and were less likely to be sensitized or to experience delayed graft function (DGF). Over a median follow-up of 5.6 years, 1256 of all recipients experienced death-censored graft failure (DCGF; 115 patients with PKD) and 1617 died (154 patients with PKD). After adjustment for demographic, dialysis, comorbid disease, surgical, and immunologic variables, patients with PKD had a lower risk of DCGF (adjusted hazard ratio [aHR], 0.73; 95% CI, 0.57 to 0.93; P=0.01) and death (aHR, 0.62; 95% CI, 0.51 to 0.75; P<0.001). In our multiadjusted model, calcineurin-inhibitor (CNI) use was associated with lower risk of DCGF (aHR, 0.45; 95% CI, 0.26 to 0.76; P=0.003), whereas HLA mismatch of five to six antigens (aHR, 2.1; 95% CI, 1.2 to 3.64; P=0.009) was associated with higher likelihood of DCGF. Notably, both pretransplant coronary artery disease (CAD) and higher BMI were associated with increased risk of death (CAD, aHR, 2.5; 95% CI, 1.69 to 3.71; P<0.001; per 1 kg/m² higher BMI, aHR, 1.07; 95% CI, 1.04 to 1.11; P<0.001), DCGF, and acute rejection. Nephrectomy at time of transplant and polycystic liver disease were not associated with DCGF/death. Incidence of post-transplant diabetes mellitus was similar between PKD and non-PKD cohorts.

Conclusions

Recipients with PKD have better long-term graft and patient survival than those with non-PKD. Standard practices of CNI use and promoting HLA match are beneficial in PKD and should continue to be promoted. Further prospective studies investigating the potential benefits of CNI use and medical/surgical interventions to address CAD and the immunologic challenges of obesity are needed.

Podcast

This article contains a podcast at https://dts.podtrac.com/redirect.mp3/www.asn-online.org/media/podcast/K360/2021_02_25_KID0001182019.mp3.

CT and MR imaging surveillance of stage 1 renal cell carcinoma after microwave ablation

OBJECTIVE

To describe the CT and MR imaging findings after microwave ablation of clinical stage 1 renal cell carcinoma (RCC).

METHODS

This single-center retrospective study was performed under a waiver of informed consent. 49 patients (38 M/11F, mean age 66 ± 9.0) with 52 cT1a RCC and 19 patients (10M/9F, mean age 67 ± 9.7) with 19 cT1b RCC were treated with percutaneous microwave ablation between January 2012 and June 2014. The size and volume of the RCC and ablation zone were measured and the kidney, ablation zones and retroperitoneum were assessed at immediate post-procedure CT and surveillance CT and MRI.

RESULTS

Median imaging follow-up was 18 months (IQR 12-28). Ablation zones were heterogeneously hyperintense on T1W and hypointense on T2W MRI and hyperdense at CT. Thin peripheral, but no internal enhancement after contrast administration signified successful ablation zones. Ablation zones decreased in size, but did not resolve during surveillance. Immediate post-procedure subcapsular gas and hematoma (5/71, 7%) resolved prior to first follow-up. Focal, enhancing soft tissue within the ablation zone, invariably along the renal margin, signified local recurrence. Local recurrence rates were higher for T1b (2/19, 11%) compared to T1a (1/52, 2%). Urinomas (4/71, 6%) decreased in size and resolved during surveillance. Retroperitoneal fat necrosis (6/71, 9%), with opposed-phase loss of T1W MRI signal, was confirmed at histology after percutaneous biopsy.

CONCLUSION

CT and MR imaging features after microwave ablation of renal cell carcinoma are predictable and reliably demonstrate treatment success, early and delayed complications, and local recurrences that can guide patient management.

Phase II trial of neoadjuvant chemohormonal therapy (NAC) in prostate cancer (PC) with response assessment using PSMA PET/MRI

334

Background: Previous studies have shown that addition of docetaxel to androgen deprivation therapy (ADT) significantly improves progression-free survival (PFS) and overall survival (OS) in men with metastatic hormone-sensitive PC. Removal of the primary may also improve outcomes by reducing tumor self-seeding. We are conducting a phase II trial in men with PC to examine the feasibility of NAC, response using PSMA PET/MRI imaging and molecular mechanisms of resistance. Methods: This is an open-label, single-arm trial. Thirty patients with newly diagnosed very high risk localized, locally advanced or oligometastatic PC will receive ADT/docetaxel for three cycles before prostatectomy. The primary endpoint is rate of complete pathologic response. Key secondary objectives include PSA recurrence at month 12 after surgery. Exploratory objectives include tumor response and response heterogeneity in primary and metastatic tumors before and after treatment assessed by PSMA PET/MRI and evaluation of gene expression signatures in cancer cells, prostate stroma, bone marrow microenvironment and circulating tumor cells. Results: To date, 26 of 30 patients have enrolled and completed treatment. Mean age was 61 and mean PSA at time of diagnosis was 32.1 ng/dl. All patients had multi-focal prostate cancer with 23/26 patients with Gleason Grade Group 5. Metastatic disease by conventional imaging was identified in 6/26 patients (5 in lymph nodes [LN] and bone, 1 in LN only). Treatment was overall well tolerated. All patients had multi-focal primary prostate cancer detected on PSMA PET/MRI. All patients had a decline in PSMA PET SUVmax in at least one intraprostatic lesion. Two patients had an increase in SUVmax in at least one intraprostatic lesion that correlated with a resistant tumor focus on histopathology. Conclusions: NAC prior to surgery generates high rates of local tumor control with a heterogeneous response between foci. Primary resistance, identified by increasing PSMA PET SUVmax, is uncommon, however incomplete responses were observed in nearly all patients, suggesting that more cycles of treatment would improve response. PSMA PET/MRI can be used to monitor response and resistance in PC. Clinical trial information: NCT03358563.

Stimulated-echo diffusion-weighted imaging with moderate b values for the detection of prostate cancer

OBJECTIVES

Conventional spin-echo (SE) DWI leads to a fundamental trade-off depending on the b value: high b value provides better lesion contrast-to-noise ratio (CNR) by sacrificing signal-to-noise ratio (SNR), image quality, and quantitative reliability. A stimulated-echo (STE) DWI acquisition is evaluated for high-CNR imaging of prostate cancer while maintaining SNR and reliable apparent diffusion coefficient (ADC) mapping.

METHODS

In this prospective, IRB-approved study, 27 patients with suspected prostate cancer (PCa) were scanned with three DWI sequences (SE b = 800 s/mm², SE b = 1500 s/mm², and STE b = 800 s/mm²) after informed consent was obtained. ROIs were drawn on biopsy-confirmed cancer and non-cancerous tissue to perform quantitative SNR, CNR, and ADC measurements. Qualitative metrics (SNR, CNR, and overall image quality) were evaluated by three experienced radiologists. Metrics were compared pairwise between the three acquisitions using a t test (quantitative metrics) and Wilcoxon rank test (qualitative metrics).

RESULTS

Quantitative measurements showed that STE DWI at b = 800 s/mm² has significantly better SNR compared to SE DWI at b = 1500 s/mm² (p < 0.0001) and comparable CNR to high-b value SE DWI at b = 1500 s/mm² (p < 0.05) in the peripheral zone. Qualitative assessment showed preference to STE b = 800 s/mm² in SNR and SE b = 1500 s/mm² in CNR. The overall image quality and lesion detectability among most readers showed no significant preference between STE b = 800 s/mm² and SE b = 1500 s/mm². Further, STE DWI had similar ADC contrast between lesion and normal tissue as SE DWI at b = 800 s/mm² (p = 0.90).

CONCLUSION

STE DWI has the potential to provide high-SNR, high-CNR imaging of prostate cancer while also enabling reliable ADC mapping.

KEY POINTS

• Quantitative analysis showed that STE DWI at b = 800 s/mm²is able to achieve simultaneously high CNR, high SNR, and reliable ADC mapping, compared to SE b = 800 s/mm²and SE b = 1500 s/mm². • Qualitative assessment by three readers showed that STE DWI at b = 800 s/mm²has significantly higher SNR than SE b = 1500 s/mm². No preference between SE b = 1500 s/mm²and STE b = 800 s/mm²was determined in terms of CNR with no missed lesions were found in both acquisitions. • A single STE DWI acquisition at moderate b value (800-1000 s/mm²) may provide sufficient image quality and quantitative reliability for prostate cancer imaging within a shorter scan time, in place of two DWI acquisitions (one with moderate b value and one with high b value).

Pharmacokinetics of Ferumoxytol in the Abdomen and Pelvis: A Dosing Study with 1.5- and 3.0-T MRI Relaxometry

Background The off-label use of ferumoxytol (FE), an intravenous iron preparation for iron deficiency anemia, as a contrast agent for MRI is increasing; therefore, it is critical to understand its pharmacokinetics. Purpose To evaluate the pharmacokinetics of FE in the abdomen and pelvis, as assessed with quantitative 1.5- and 3.0-T MRI relaxometry. Materials and Methods R2*, an MRI technique used to estimate tissue iron content in the abdomen and pelvis, was performed at 1.5 and 3.0 T in 12 healthy volunteers between April 2015 and January 2016. Volunteers were randomly assigned to receive an FE dose of 2 mg per kilogram of body weight (FE_2mg) or 4 mg/kg (FE_4mg). MRI was repeated at 1.5 and 3.0 T for each volunteer at five time points: days 1, 2, 4, 7, and 30. A radiologist experienced in MRI relaxometry measured R2* in organs of the mononuclear phagocyte system (MPS) (ie, liver, spleen, and bone marrow), non-MPS anatomy (kidney, pancreas, and muscle), inguinal lymph nodes (LNs), and blood pool. A paired Student t test was used to compare changes in tissue R2*. Results Volunteers (six female; mean age, 44.3 years ± 12.2 [standard deviation]) received either FE_{2 mg} (n = 5) or FE_{4 mg} (n = 6). Overall R2* trend analysis was temporally significant (P < .001). Time to peak R2* in the MPS occurred on day 1 for FE_2mg and between days 1 and 4 for FE_4mg (P < .001 to P < .002). Time to peak R2* in non-MPS anatomy, LNs, and blood pool occurred on day 1 for both doses (P < .001 to P < .09). Except for the spleen (at 1.5 T) and liver, MPS R2* remained elevated through day 30 for both doses (P = .02 to P = .03). Except for the kidney and pancreas, non-MPS, LN, and blood pool R2* returned to baseline levels between days 2 and 4 at FE_2mg (P = .06 to P = .49) and between days 4 and 7 at FE_4mg (P = .06 to P = .63). There was no difference in R2* change between non-MPS and LN R2* at any time (range, 1-71 sec^-1 vs 0-50 sec^-1; P = .06 to P = .97). Conclusion The pharmacokinetics of ferumoxytol in lymph nodes are distinct from those in mononuclear phagocyte system (MPS) organs, parallel non-MPS anatomy, and the blood pool. © RSNA, 2019 Online supplemental material is available for this article.

Salt bridge impact on global rigidity and thermostability in thermophilic citrate synthase

It has been suggested that structural rigidity is connected to thermostability, e.g. in enzymes from thermophilic microorganisms. We examine the importance of correctly handling salt bridges, and interactions which we term 'strong polars', when constructing the constraint network for global rigidity analysis in these systems. Through a comparison of rigidity in citrate synthases, we clarify the relationship between rigidity and thermostability. In particular, with our corrected handling of strong polar interactions, the difference in rigidity between mesophilic and thermophilic structures is detected more clearly than in previous studies. The increase in rigidity did not detract from the functional flexibility of the active site in all systems once their respective temperature range had been reached. We then examine the distribution of salt bridges in thermophiles that were previously unaccounted for in flexibility studies. We show that in hyperthermophiles these have stabilising roles in the active site; occuring in close proximity to key residues involved in catalysis and binding of the protein.

Mri-based cancer lesion analysis with 3d printed patient specific prostate cutting guides

Purpose: MRI methods have improved diagnosis and treatment planning for prostate cancer. However, validation and standardization is needed to encourage widespread adoption of these methods. The purpose of this study was to improve validation methods by creating a prostate cutting guide and to develop a method for 3D comparison between MRI data and post-prostatectomy histological tissue slices. Methods: Prostate Specific Membrane Antigen (PSMA) Positron Emission Tomography (PET)/MRI was performed on 10 patients with prostate cancer before and after chemohormonal treatment. Post-treatment images were used to design patient-specific prostate cutting guides that were used to create uniform thickness sections of surgically removed prostates. The thickness of the prostate tissue slices matched the imaging slice thickness so that comparisons could be made between MRI results and histopathological study results. A method was also developed to compare post-slicing prostate bulk geometry with the predicted MRI prostate geometry. Results: The prostate cutting guides were used to successfully section the prostate for histopathogical evaluation and slice-by-slice MRI comparison. Surface comparison results displayed an average dimensional difference of 1.99 ± 3.19 mm between MRI and post-prostatectomy slice reconstruction prostate geometries. Conclusion: MRI-based prostate cutting guides were designed, fabricated, and implemented in a study examining the utility and accuracy of MRI for the detection of prostate cancer. Furthermore, a three-dimensional part comparison method was developed, which can be used for validation of MRI with pathological and histological data. Future work will analyze more subjects to examine the effectiveness of these guides for histopathological prostate analysis with MRI and PET/MRI.

Bosniak Classification of Cystic Renal Masses, Version 2019: An Update Proposal and Needs Assessment

Cystic renal cell carcinoma (RCC) is almost certainly overdiagnosed and overtreated. Efforts to diagnose and treat RCC at a curable stage result in many benign neoplasms and indolent cancers being resected without clear benefit. This is especially true for cystic masses, which compared with solid masses are more likely to be benign and, when malignant, less aggressive. For more than 30 years, the Bosniak classification has been used to stratify the risk of malignancy in cystic renal masses. Although it is widely used and still effective, the classification does not formally incorporate masses identified at MRI or US or masses that are incompletely characterized but are highly likely to be benign, and it is affected by interreader variability and variable reported malignancy rates. The Bosniak classification system cannot fully differentiate aggressive from indolent cancers and results in many benign masses being resected. This proposed update to the Bosniak classification addresses some of these shortcomings. The primary modifications incorporate MRI, establish definitions for previously vague imaging terms, and enable a greater proportion of masses to enter lower-risk classes. Although the update will require validation, it aims to expand the number of cystic masses to which the Bosniak classification can be applied while improving its precision and accuracy for the likelihood of cancer in each class.

Tumor location does not impact oncologic outcomes for percutaneous microwave ablation of clinical T1a renal cell carcinoma

OBJECTIVE

To evaluate the impact of anterior tumor location on oncologic efficacy, complication rates, and procedure duration for 151 consecutive biopsy-proven clinical T1a renal cell carcinoma (RCC) treated with percutaneous microwave (MW) ablation.

METHODS

This single-center retrospective study was performed under a waiver of informed consent. One hundred forty-eight consecutive patients (103 M/45 F; median age 67 years, IQR 61-73) with 151 cT1a biopsy-proven RCC (median diameter 2.4 cm, IQR 1.9-3.0) were treated with percutaneous MW ablation between March 2011 and August 2017. Patient and procedural data collected included Charlson comorbidity index (CCI), RENAL nephrometry score (NS), use of hydrodisplacement, MW antennas/generator output/time, and procedure time (PT). Data were stratified by anterior, posterior, and midline tumor location and compared with the Kruskal-Wallis or chi-squared tests. The Kaplan-Meier method was used for survival analyses.

RESULTS

Tumor size, NS, and use/volume of hydrodisplacement were similar for posterior and anterior tumors (p > 0.05). Patients with anterior tumors had a higher CCI (3 vs 4, p = 0.001). Median PT for posterior and anterior tumors was similar (100 vs 108 min, p = 0.26). Single session technical success and primary efficacy were achieved for all 151 tumors including 61 posterior and 67 anterior tumors. The 4 (3%) Clavien III-IV complications and 6 (4%) local recurrences were not associated with tumor location (p > 0.05). Three-year RFS, CSS, and OS were 95% (95% CI 0.87, 0.98), 100% (95% CI 1.0, 1.0), and 96% (95% CI 0.89, 0.98), respectively.

CONCLUSIONS

The safety and efficacy of percutaneous microwave ablation for anterior and posterior RCC are similar.

KEY POINTS

• The safety profile for percutaneous microwave ablation of anterior and posterior T1a renal cell carcinoma is equivalent. • Percutaneous microwave ablation of T1a renal cell carcinoma provides durable oncologic control regardless of tumor location. • Placement of additional microwave antennas and use of hydrodisplacement are associated with longer procedure times.

Comparison of Displacement Tracking Algorithms for in Vivo Electrode Displacement Elastography

Hepatocellular carcinoma and liver metastases are common hepatic malignancies presenting with high mortality rates. Minimally invasive microwave ablation (MWA) yields high success rates similar to surgical resection. However, MWA procedures require accurate image guidance during the procedure and for post-procedure assessments. Ultrasound electrode displacement elastography (EDE) has demonstrated utility for non-ionizing imaging of regions of thermal necrosis created with MWA in the ablation suite. Three strategies for displacement vector tracking and strain tensor estimation, namely coupled subsample displacement estimation (CSDE), a multilevel 2-D normalized cross-correlation method, and quality-guided displacement tracking (QGDT) have previously shown accurate estimations for EDE. This paper reports on a qualitative and quantitative comparison of these three algorithms over 79 patients after an MWA procedure. Qualitatively, CSDE presents sharply delineated, clean ablated regions with low noise except for the distal boundary of the ablated region. Multilevel and QGDT contain more visible noise artifacts, but delineation is seen over the entire ablated region. Quantitative comparison indicates CSDE with more consistent mean and standard deviations of region of interest within the mass of strain tensor magnitudes and higher contrast, while Multilevel and QGDT provide higher CNR. This fact along with highest success rates of 89% and 79% on axial and lateral strain tensor images for visualization of thermal necrosis using the Multilevel approach leads to it being the best choice in a clinical setting. All methods, however, provide consistent and reproducible delineation for EDE in the ablation suite.

Society of Abdominal Radiology disease-focused panel on renal cell carcinoma: update on past, current, and future goals

The disease-focused panel (DFP) program was created by the Society of Abdominal Radiology (SAR) as a mechanism to "improve patient care, education, and research" in a "particular disease or a particular aspect of a disease". The DFP on renal cell carcinoma (RCC) was proposed in 2014 and has been functional for 4 years. Although nominally focused on RCC, the scope of the DFP has included indeterminate renal masses because many cannot be assigned a specific diagnosis when detected. Since its founding, the DFP has been active in a variety of clinical, research, and educational projects to optimize the care of patients with known or suspected RCC. The DFP is utilizing multi-institutional and cross-disciplinary collaboration to differentiate benign from malignant disease, optimize the management of early stage RCC, and ultimately to differentiate indolent from aggressive cancers. Several additional projects have worked to develop a quantitative biomarker that predicts metastatic RCC response to anti-angiogenic therapy. While disease focus is the premise by which all DFPs are created, it is likely that in the future the RCC DFP will need to expand or create new panels that will focus on other specific aspects of RCC-a result that the program's founders envisioned. New knowledge creates a need for more focus.

Combination transarterial chemoembolization and microwave ablation improves local tumor control for 3- to 5-cm hepatocellular carcinoma when compared with transarterial chemoembolization alone

PURPOSE

To compare transarterial chemoembolization (TACE) monotherapy to combination TACE and microwave ablation (MWA) for local control of 3- to 5-cm hepatocellular carcinoma (HCC).

METHODS

Patients with HCC between 3 and 5 cm treated with TACE monotherapy or combination TACE + MWA at a single institution between 2007 and 2016 were retrospectively reviewed. Twenty-four HCCs (median diameter 3.8 cm) in 16 patients (13 males; median age 64 years) were treated using TACE monotherapy. Combination TACE + MWA was used to treat 23 HCCs (median diameter 4.2 cm) in 22 patients (18 males; median age 61 years). Microwave ablation was performed at a target time of two weeks following TACE. Individual tumors were followed by serial contrast-enhanced CT or MR. Response to treatment was evaluated on a tumor-by-tumor basis using mRECIST criteria with the primary outcome being local tumor progression (LTP). Data were analyzed using Fisher's exact test for categorical variables and Wilcoxon rank sum test for continuous variables. Time to LTP was estimated with the Kaplan-Meier method.

RESULTS

Relative to TACE monotherapy, TACE + MWA provided a trend toward both a lower rate of LTP (34.8% vs. 62.5%, p = 0.11) and a higher complete response rate (65.2% vs. 37.5%; p = 0.12). Time to LTP (22.3 months vs. 4.2 months; p = 0.001) was significantly longer in the TACE + MWA group compared to TACE monotherapy.

CONCLUSIONS

Combination therapy with TACE and microwave ablation improves local control and increases time to LTP for 3-5 cm HCC.

Stimulated echo based mapping (STEM) of T1 , T2 , and apparent diffusion coefficient: validation and protocol optimization

PURPOSE

To present a stimulated-echo based mapping (STEM) approach for simultaneous T₁ , T₂ , and ADC mapping.

METHODS

Diffusion-weighted stimulated-echo images with various combinations of mixing time (TM), TE, and b-value were acquired to enable simultaneous mapping of T₁ , T₂ , and ADC. The proposed STEM method was performed by densely sampling the TM-TE-b space in a phantom and in brain and prostate of healthy volunteers. T₁ , T₂ , and ADC from STEM were compared to reference mapping methods. Additionally, protocol optimization was performed to enable rapid STEM acquisition within 2 min by sparsely sampling the TM-TE-b space. The T₁ , T₂ , and ADC measurements from rapid acquisitions were compared to the densely sampled STEM for evaluation. Finally, a patient with biopsy-proven high-risk prostate cancer was imaged to demonstrate the ability of STEM to differentiate cancer and healthy tissues.

RESULTS

Relative to the reference measurements, densely sampled STEM provided accurate quantitative T₁ , T₂ , and ADC mapping in phantoms (R²  = 0.999, slope between 0.97-1.03), as well as in brain and prostate. Further, the T₁ , T₂ , and ADC measurements from the optimized rapid STEM acquisitions agreed closely with densely sampled STEM. Finally, STEM showed decreased T₂ and ADC in prostate cancer compared to healthy prostate tissue.

CONCLUSION

STEM provides accurate simultaneous mapping of T₁ , T₂ , and ADC. This method may enable rapid and accurate multi-parametric tissue characterization for clinical and research applications.

Renal mass biopsy and thermal ablation: should biopsy be performed before or during the ablation procedure?

PURPOSE

To determine if renal mass biopsy should be performed before or during the ablation procedure with emphasis on complications and rate of ablation for renal cell carcinomas (RCC), benign tumors, and small renal masses without a histologic diagnosis.

METHODS

This HIPAA-compliant, single-center retrospective study was performed under a waiver of informed consent from the institutional review board. Two hundred eighty-four consecutive patients with a small renal mass (≤4.0 cm) treated with percutaneous thermal ablation between January 2001 and January 2015 were included. Two cohorts were identified based upon the timing of renal mass biopsy: separate session two weeks prior to ablation and same session obtained immediately preceding ablation. Clinical and pathologic data were collected including risk factors for non-diagnostic biopsy. Two-sided t test, χ ² test or Fischer's exact tests were used to evaluate differences between cohorts. Univariate and multivariate logistic regression models were constructed.

RESULTS

A histologic diagnostic was achieved more frequently in the separate session cohort [210/213 (98.6%) vs. 60/71 (84.3%), p < 0.0001]. The rate of ablation of RCC was higher in the separate session group [201/213 (94.4%) vs. 46/61 (64.7%), p = 0.001]. The rate of ablation for benign tumors [14/71 (19.7%) vs. 6/213 (2.8%), p < 0.0001] and small renal masses without a histologic diagnosis [3/213 (1.4%) vs. 11/71 (15.5%), p < 0.0001] was higher in the same session cohort. There were no high-grade complications in either cohort.

CONCLUSION

Performing renal mass biopsy prior to the day of ablation is safe, increases the rate of histologic diagnosis, and reduces the rate of ablation for benign tumors and small renal masses without a histologic diagnosis.

Effect of Tumor Complexity and Technique on Efficacy and Complications after Percutaneous Microwave Ablation of Stage T1a Renal Cell Carcinoma: A Single-Center, Retrospective Study

Purpose To evaluate the effects of tumor complexity and technique on early and midterm oncologic efficacy and rate of complications for 100 consecutive biopsy-proved stage T1a renal cell carcinomas (RCCs) treated with percutaneous microwave ablation. Materials and Methods This HIPAA-compliant, single-center retrospective study was approved by the institutional review board. The requirement to obtain informed consent was waived. Ninety-six consecutive patients (68 men, 28 women; mean age, 66 years ± 9.4) with 100 stage T1a N0M0 biopsy-proved RCCs (median diameter, 2.6 cm ± 0.8) underwent percutaneous microwave ablation between March 2011 and June 2015. Patient and procedural data were collected, including body mass index, comorbidities, tumor histologic characteristics and grade, RENAL nephrometry score, number of antennas, generator power, and duration of ablation. Technical success, local tumor progression, and presence of complications were assessed at immediate and follow-up imaging. The Kaplan-Meier method was used for survival analyses. Results Technical success was achieved for all 100 tumors (100%), including 47 moderately and five highly complex RCCs. Median clinical and imaging follow-up was 17 months (range, 0-48 months) and 15 months (range, 0-44 months), respectively. No change in estimated glomerular filtration rate was noted after the procedure (P = .49). There were three (3%) procedure-related complications and six (6%) delayed complications, all urinomas. One case of local tumor progression (1%) was identified 25 months after the procedure. Three-year local progression-free survival, cancer-specific survival, and overall survival were 88% (95% confidence interval: 0.52%, 0.97%), 100% (95% confidence interval: 1.0%, 1.0%), and 91% (95% confidence interval: 0.51%, 0.99%), respectively. Conclusion Percutaneous microwave ablation is an effective and safe treatment option for stage T1a RCC, regardless of tumor complexity. Long-term follow-up is needed to establish durable oncologic efficacy and survival relative to competing ablation modalities and surgery. ^© RSNA, 2017.

Post-Procedure Evaluation of Microwave Ablations of Hepatocellular Carcinomas Using Electrode Displacement Elastography

Microwave ablation has been used clinically as an alternative to surgical resection. However, lack of real-time imaging to assess treated regions may compromise treatment outcomes. We previously introduced electrode displacement elastography (EDE) for strain imaging and verified its feasibility in vivo on porcine animal models. In this study, we evaluated EDE on 44 patients diagnosed with hepatocellular carcinoma, treated using microwave ablation. The ablated region was identified on EDE images for 40 of the 44 patients. Ablation areas averaged 13.38 ± 4.99 cm² on EDE, compared with 7.61 ± 3.21 cm² on B-mode imaging. Contrast and contrast-to-noise ratios obtained with EDE were 232% and 98%, respectively, significantly higher than values measured on B-mode images (p < 0.001). This study indicates that EDE is feasible in patients and provides improved visualization of the ablation zone compared with B-mode ultrasound.

Hepatic Tumor Ablation

Tumor ablation is a safe and effective treatment available in the multidisciplinary care of the surgical oncology patient. The role of ablation is well established in the treatment of hepatocellular carcinoma and is becoming more accepted in the treatment of various malignancies metastatic to the liver, in particular colorectal cancer. Understanding the underlying technology, achieving appropriate applicator placement, using maximum energy delivery to create margins, and performing necessary adjunctive maneuvers are all required for successful tumor ablation.

Percutaneous microwave ablation of T1a and T1b renal cell carcinoma: short-term efficacy and complications with emphasis on tumor complexity and single session treatment

PURPOSE

To update the oncologic outcomes and safety for microwave (MW) ablation of T1a (≤4.0 cm) and T1b (4.1-7.0 cm) renal cell carcinoma (RCC) with emphasis on tumor complexity and single session treatment.

MATERIALS AND METHODS

Retrospective review of 29 consecutive patients (30 tumors) with localized (NOMO) RCC (23 T1a; 7 T1b) treated with percutaneous MW ablation between 3/2013 and 6/2014. Primary outcomes investigated were technical success, local tumor progression (LTP), and complications. Technical success was assessed with contrast-enhanced computed tomography (CECT) immediately after MW ablation. Presence of LTP was assessed with CECT or contrast-enhanced magnetic resonance at 6-month target intervals for the first two years and annually thereafter. Complications were categorized using the Clavien-Dindo classification system.

RESULTS

Median tumor diameter was 2.8 cm [IQR 2.1-3.3] for T1a and 4.7 cm [IQR 4.1-5.7] for T1b tumors. Median RENAL nephrometry score was 7 [IQR 4-8] for T1a tumors and 9 [IQR 6.25-9.75] for T1b tumors. Technical success was achieved for 22 T1a (96%) and 7 T1b (100%) tumors. There were no LTP during a median imaging follow-up of 12.0 months [IQR 6-18] for the 23 patients (24 tumors) with greater than 6 months of follow-up. There were three Clavien-Dindo grade I-II complication (10%) and no Clavien-Dindo grade III-V complications (0%). All but two patients (93%) are alive without metastatic disease; two patients died after 12-month follow-up of causes unrelated to the MW ablation.

CONCLUSION

Percutaneous MW ablation appears to be a safe and effective treatment option for low, moderate, and highly complex T1a and T1b RCC in early follow-up.

Percutaneous biopsy in the abdomen and pelvis: a step-by-step approach

Percutaneous abdominal biopsies provide referring physicians with valuable diagnostic and prognostic information that guides patient care. All biopsy procedures follow a similar process that begins with the preprocedure evaluation of the patient and ends with the postprocedure management of the patient. In this review, a step-by-step approach to both routine and challenging abdominal biopsies is covered with an emphasis on the differences in biopsy devices and imaging guidance modalities. Adjunctive techniques that may facilitate accessing a lesion in a difficult location or reduce procedure risk are described. An understanding of these concepts will help maintain the favorable safety profile and high diagnostic yield associated with percutaneous biopsies.

Microwave versus Radiofrequency Ablation Treatment for Hepatocellular Carcinoma: A Comparison of Efficacy at a Single Center

PURPOSE

To compare efficacy and major complication rates of radiofrequency (RF) and microwave (MW) ablation for treatment of hepatocellular carcinoma (HCC).

MATERIALS AND METHODS

This retrospective single-center study included 69 tumors in 55 patients treated by RF ablation and 136 tumors in 99 patients treated by MW ablation between 2001 and 2013. RF and MW ablation devices included straight 17-gauge applicators. Overall survival and rates of local tumor progression (LTP) were evaluated using Kaplan-Meier techniques with Cox proportional hazard ratio (HR) models and competing risk regression of LTP.

RESULTS

RF and MW cohorts were similar in age (P = .22), Model for End-Stage Liver Disease score (P = .24), and tumor size (mean 2.4 cm [range, 0.6-4.5 cm] and 2.2 cm [0.5-4.2 cm], P = .09). Median length of follow-up was 31 months for RF and 24 months for MW. Rate of LTP was 17.7% with RF and 8.8% with MW. Corresponding HR from Cox and competing risk models was 2.17 (95% confidence interval [CI], 1.04-4.50; P = 0.04) and 2.01 (95% CI, 0.95-4.26; P = .07), respectively. There was improved survival for patients treated with MW ablation, although this was not statistically significant (Cox HR, 1.59 [95% CI, 0.91-2.77; P = .103]). There were few major (≥ grade C) complications (2 for RF, 1 for MW; P = .28).

CONCLUSIONS

Treating HCC percutaneously with RF or MW ablation was associated with high primary efficacy and durable response, with lower rates of LTP after MW ablation.

Liver Ablation: Best Practice

Tumor ablation in the liver has evolved to become a well-accepted tool in the management of increasing complex oncologic patients. At present, percutaneous ablation is considered first-line therapy for very early and early hepatocellular carcinoma and second-line therapy for colorectal carcinoma liver metastasis. Because thermal ablation is a treatment option for other primary and secondary liver tumors, an understanding of the underlying tumor biology is important when weighing the potential benefits of ablation. This article reviews ablation modalities, indications, patient selection, and imaging surveillance, and emphasizes technique-specific considerations for the performance of percutaneous ablation.

X-ray, spectroscopic and normal-mode dynamics of calexcitin: structure-function studies of a neuronal calcium-signalling protein

The protein calexcitin was originally identified in molluscan photoreceptor neurons as a 20 kDa molecule which was up-regulated and phosphorylated following a Pavlovian conditioning protocol. Subsequent studies showed that calexcitin regulates the voltage-dependent potassium channel and the calcium-dependent potassium channel as well as causing the release of calcium ions from the endoplasmic reticulum (ER) by binding to the ryanodine receptor. A crystal structure of calexcitin from the squid Loligo pealei showed that the fold is similar to that of another signalling protein, calmodulin, the N- and C-terminal domains of which are known to separate upon calcium binding, allowing interactions with the target protein. Phosphorylation of calexcitin causes it to translocate to the cell membrane, where its effects on membrane excitability are exerted and, accordingly, L. pealei calexcitin contains two protein kinase C phosphorylation sites (Thr61 and Thr188). Thr-to-Asp mutations which mimic phosphorylation of the protein were introduced and crystal structures of the corresponding single and double mutants were determined, which suggest that the C-terminal phosphorylation site (Thr188) exerts the greatest effects on the protein structure. Extensive NMR studies were also conducted, which demonstrate that the wild-type protein predominantly adopts a more open conformation in solution than the crystallographic studies have indicated and, accordingly, normal-mode dynamic simulations suggest that it has considerably greater capacity for flexible motion than the X-ray studies had suggested. Like calmodulin, calexcitin consists of four EF-hand motifs, although only the first three EF-hands of calexcitin are involved in binding calcium ions; the C-terminal EF-hand lacks the appropriate amino acids. Hence, calexcitin possesses two functional EF-hands in close proximity in its N-terminal domain and one functional calcium site in its C-terminal domain. There is evidence that the protein has two markedly different affinities for calcium ions, the weaker of which is most likely to be associated with binding of calcium ions to the protein during neuronal excitation. In the current study, site-directed mutagenesis has been used to abolish each of the three calcium-binding sites of calexcitin, and these experiments suggest that it is the single calcium-binding site in the C-terminal domain of the protein which is likely to have a sensory role in the neuron.

Effect of hepatocyte-specific gadolinium-based contrast agents on hepatic fat-fraction and R2(⁎)

The purpose of this work was to investigate the effect of a hepatocyte-specific gadolinium based contrast agent (GBCA) on quantitative hepatic fat-fraction (FF) and R2* measurements. Fifty patients were imaged at 1.5T, using chemical-shift encoded water-fat MRI with low (5°) and high (15°) flip angles (FA), both before and after administration of a hepatocyte-specific GBCA (gadoxetic acid). Low and high FA, pre- and post-contrast FF and R2* values were measured for each subject. Available serum laboratory studies related to liver disease were also recorded. Linear regression and Bland-Altman analysis were performed to compare measurements. Hepatic FF was unaffected by GBCA at low FA (slope=1.02±0.02, p=0.32). FF was overestimated at high FA pre-contrast (slope=1.33±0.03, p<10(-10)), but underestimated post-contrast (slope=0.81±0.02, p<10(-10)). Hepatic R2* was unaffected by FA (mean difference±95% CI pre-contrast:2.2±4.9s(-1), post-contrast:2.8±3.6s(-1)), but increased post-contrast in patients with total bilirubin <2.5mg/dL (ΔR2*=13.4±12.7s(-1)). Regression analysis of serum values demonstrated a correlation of post-contrast change in R2* with total bilirubin (p<0.01) and model for end-stage liver disease (MELD) score (p≈0.01). In conclusion, GBCA has no effect on hepatic FF at low FA due to a lack of T1-weighting, potentially allowing flexibility for FF imaging with hepatobiliary imaging protocols. Hepatic R2* increased significantly after GBCA administration, particularly in the biliary tree. Therefore, R2* maps should be obtained prior to contrast administration.

Microwave ablation of giant hepatic cavernous hemangiomas

PURPOSE

This study was designed to explore the safety and efficacy of percutaneous microwave (MW) ablation as an alternative treatment for symptomatic giant hepatic hemangiomas.

METHODS

Patients (n = 7; 6 females, 1 male; mean age = 44 years) with symptomatic, giant hemangiomas (n = 8) were treated with ultrasound-guided percutaneous MW ablation and followed for a mean of 18 months. Patient pain was recorded both before and after the procedure according to the 10-point visual analog scale. All patients were treated using one or three gas-cooled 17-gauge antennas powered by a 2.4-GHz generator (Neuwave Medical, Madison, WI). Mean ablation time was 11.6 min. Four patients received hydrodissection to protect the abdominal wall, colon, or gallbladder (5 % dextrose in water, mean volume 900 mL). Immediate postablation biphasic CT of the abdomen was performed, and four of seven patients have undergone delayed follow-up imaging.

RESULTS

All ablations were technically successful with no major or minor complications. Average pain score decreased from 4.6 to 0.9 (p < 0.05), and six of seven patients report resolution or improvement of symptoms at 18-month average follow-up (range 1-33 months). Immediately postablation, mean tumor diameter decreased 25 % (from 7.3 to 5.5 cm, p < 0.05) and volume decreased 62 % (from 301 to 113 cm(3), p < 0.05).

DISCUSSION

In this series, percutaneous MW ablation was safe, well-tolerated, and effective in markedly shrinking large hepatic hemangiomas and improving symptoms in most patients.

Inhibition of HIV-1 protease: the rigidity perspective

MOTIVATION

HIV-1 protease is a key drug target due to its role in the life cycle of the HIV-1 virus. Rigidity analysis using the software First is a computationally inexpensive method for inferring functional information from protein crystal structures. We evaluate the rigidity of 206 high-resolution (2 Å or better) X-ray crystal structures of HIV-1 protease and compare the effects of different inhibitors binding to the enzyme.

RESULTS

Inhibitor binding has little effect on the overall rigidity of the protein homodimer, including the rigidity of the active site. The principal effect of inhibitor binding on rigidity is to constrain the flexibility of the β-hairpin flaps, which move to allow access to the active site of the enzyme. We show that commercially available antiviral drugs which target HIV-1 protease can be divided into two classes, those which significantly affect flap rigidity and those which do not. The non-peptidic inhibitor tipranavir is distinctive in its consistently strong effect on flap rigidity.

CONTACT

jack.heal@warwick.ac.uk; r.roemer@warwick.ac.uk

SUPPLEMENTARY INFORMATION

Supplementary data are available at Bioinformatics online.

Rapid simulation of protein motion: merging flexibility, rigidity and normal mode analyses

Protein function frequently involves conformational changes with large amplitude on timescales which are difficult and computationally expensive to access using molecular dynamics. In this paper, we report on the combination of three computationally inexpensive simulation methods--normal mode analysis using the elastic network model, rigidity analysis using the pebble game algorithm, and geometric simulation of protein motion--to explore conformational change along normal mode eigenvectors. Using a combination of ElNemo and First/Froda software, large-amplitude motions in proteins with hundreds or thousands of residues can be rapidly explored within minutes using desktop computing resources. We apply the method to a representative set of six proteins covering a range of sizes and structural characteristics and show that the method identifies specific types of motion in each case and determines their amplitude limits.