BACKGROUND AND PURPOSE: Controversy exists as to whether ADC histograms are capable to distinguish human papillomaviruspositive (HPV1) from human papillomavirus-negative (HPV-) oropharyngeal squamous cell carcinoma. We investigated how the choice of b-values influences the capability of ADC histograms to distinguish between the two tumor types.MATERIALS AND METHODS: Thirty-four consecutive patients with histologically proved primary oropharyngeal squamous cell carcinoma (11 HPV1 and 23 HPV-) underwent 3T MR imaging with a single-shot EPI DWI sequence with 6 b-values (0, 50, 100, 500, 750, 1000 s/mm 2 ). Monoexponentially calculated perfusion-sensitive (including b¼0 s/mm 2 ) and perfusion-insensitive/true diffusion ADC maps (with b $ 100 s/mm 2 as the lowest b-value) were generated using Matlab. The choice of b-values included 2 b-values (ADC b0-1000 , ADC b100-1000 , ADC b500-1000 , ADC b750-1000 ) and 3-6 b-values (ADC b0-750-1000 , ADC b0-500-750-1000 , ADC b0-50-100-1000 , ADC b0-50-100-750-1000 , ADC b0-50-100-500-750-1000 ). Readers blinded to the HPV-status contoured all tumors. ROIs were then copied onto ADC maps, and their histograms were compared.RESULTS: ADC histogram metrics in HPV1 and HPV-oropharyngeal squamous cell carcinoma changed significantly depending on the b-values. The mean ADC was lower, and skewness was higher in HPV1 than in HPV-oropharyngeal squamous cell carcinoma only for ADC b0-1000, ADC b0-750-1000 , and ADC b0-500-750-1000 (P , .05), allowing distinction between the 2 tumor types. Kurtosis was significantly higher in HPV1 versus HPV-oropharyngeal squamous cell carcinoma for all b-value combinations except 2 perfusioninsensitive maps (ADC b500-1000 and ADC b750-1000 ). Among all b-value combinations, kurtosis on ADC b0-1000 had the highest diagnostic performance to distinguish HPV1 from HPV-oropharyngeal squamous cell carcinoma (area under the curve ¼ 0.893; sensitivity ¼ 100%, specificity ¼ 82.6%). Acquiring multiple b-values for ADC calculation did not improve the distinction between HPV1 and HPV-oropharyngeal squamous cell carcinoma. CONCLUSIONS:The choice of b-values significantly affects ADC histogram metrics in oropharyngeal squamous cell carcinoma. Distinguishing HPV1 from HPV-oropharyngeal squamous cell carcinoma is best possible on the ADC b0-1000 map.ABBREVIATIONS: AJCC ¼ American Joint Committee on Cancer; AUC ¼ area under the curve; HNSCC ¼ head and neck squamous cell carcinoma; HPV1 ¼ human papillomavirus positive; HPV-¼ human papillomavirus negative; OPSCC ¼ oropharyngeal squamous cell carcinoma

PurposeHigh-intensity focused ultrasound (HIFU) is challenging in the liver due to the respiratory motion and risks of near-/far-field burns, particularly on the ribs. We implemented a novel design of a HIFU phased-array transducer, dedicated to transcostal hepatic thermo-ablation. Due to its large acoustic window and strong focusing, the transducer should perform safely for this application.Material and MethodsThe new HIFU transducer is composed of 256 elements distributed on 5 concentric segments of a specific radius (either 100, 111, or 125 mm). It has been optimally shaped to fit the abdominal wall. The shape and size of the acoustic elements were optimized for the largest emitting surface and the lowest symmetry. Calibration tests have been conducted on tissue-mimicking gels under 3-T magnetic resonance (MR) guidance. In-vivo MR-guided HIFU treatment was conducted in two pigs, aiming to create thermal ablation deep in the liver without significant side effects. Imaging follow-up was performed at D0 and D7. Sacrifice and post-mortem macroscopic examination occurred at D7, with the ablated tissue being fixed for pathology.ResultsThe device showed −3-dB focusing capacities in a volume of 27 × 46 × 50 mm3 as compared with the numerical simulation volume of 18 × 48 × 60 mm3. The shape of the focal area was in millimeter-range agreement with the numerical simulations. No interference was detected between the HIFU sonication and the MR acquisition. In vivo, the temperature elevation in perivascular liver parenchyma reached 28°C above physiological temperature, within one breath-hold. The lesion was visible on Gd contrast-enhanced MRI sequences and post-mortem examination. The non-perfused volume was found in pig #1 and pig #2 of 8/11, 6/8, and 7/7 mm along the LR, AP, and HF directions, respectively. No rib burns or other near-field side effects were visually observed on post-mortem gross examination. High-resolution contrast-enhanced 3D MRI indicated a minor lesion on the sternum.ConclusionThe performance of this new HIFU transducer has been demonstrated in vitro and in vivo. The transducer meets the requirement to perform thermal lesions in deep tissues, without the need for rib-sparing means.

Background: HIFU ablation of liver malignancies is particularly challenging due to respiratory motion, high tissue perfusion and the presence of the rib cage. Based on our previous development of a super-convergent phased-array transducer, we aimed to further investigate, in vivo, its applicability to deep intrahepatic targets. Methods: In a series of six pigs, a pseudo-tumor model was used as target, visible both on intra-operatory MRI and post-mortem gross pathology. The transcostal MRgHIFU ablation was prescribed coplanar with the pseudo-tumor, either axial or sagittal, but deliberately shifted 7 to 18 mm to the side. No specific means of protection of the ribs were implemented. Post-treatment MRI follow-up was performed at D7, followed by animal necropsy and gross pathology of the liver. Results: The pseudo-tumor was clearly identified on T1w MR imaging and subsequently allowed the MRgHIFU planning. The peak temperature at the focal point ranged from 58–87 °C. Gross pathology confirmed the presence of the pseudo-tumor and the well-delineated MRgHIFU ablation at the expected locations. Conclusions: The specific design of the transducer enabled a reliable workflow. It demonstrated a good safety profile for in vivo transcostal MRgHIFU ablation of deep-liver targets, graded as challenging for standard surgery.

Design, embodiment, and experimental study of a novel concept of extracorporeal phased array ultrasound transducer for prostate cancer regional deep hyperthermia treatments using a transperineal acoustic window is presented. An optimized design of hyperthermia applicator was derived from a modelling software where acoustic and thermal fields were computed based on anatomical data. Performance tests have been experimentally conducted on gel phantoms and tissues, under 3T MRI guidance using PRFS thermometry. Feedback controlled hyperthermia (ΔT = 5 °C during 20min) was performed on two ex vivo lamb carcasses with prostate mimicking pelvic tissue, to demonstrate capability of spatio-temporal temperature control and to assess potential risks and side effects. Our optimization approach yielded a therapeutic ultrasound transducer consisting of 192 elements of variable shape and surface, pseudo randomly distributed on 6 columns, using a frequency of 700 kHz. Radius of curvature was 140 mm and active water circulation was included for cooling. The measured focusing capabilities covered a volume of 24 × 50 × 60 mm3. Acoustic coupling of excellent quality was achieved. No interference was detected between sonication and MR acquisitions. On ex vivo experiments the target temperature elevation of 5 °C was reached after 5 min and maintained during another 15 min with the predictive temperature controller showing 0.2 °C accuracy. No significant temperature rise was observed on skin and bonny structures. Reported results represent a promising step toward the implementation of transperineal ultrasound hyperthermia in a pilot study of reirradiation in prostate cancer patients.