Targeted prostate biopsy and MR-guided therapy for prostate cancer

Prostate cancer is the most commonly diagnosed noncutaneous cancer and second-leading cause of death in men. Many patients with clinically organ-confined prostate cancer undergo definitive treatment of the whole gland including radical prostatectomy, radiation therapy, and cryosurgery. Active surveillance is a growing alternative option for patients with documented low-volume, low-grade prostate cancer. With recent advances in software and hardware of MRI, multiparametric MRI of the prostate has been shown to improve the accuracy in detecting and characterizing clinically significant prostate cancer. Targeted biopsy is increasingly utilized to improve the yield of MR-detected, clinically significant prostate cancer and to decrease in detection of indolent prostate cancer. MR-guided targeted biopsy techniques include cognitive MR fusion TRUS biopsy, in-bore transrectal targeted biopsy using robotic transrectal device, and in-bore direct MR-guided transperineal biopsy with a software-based transperineal grid template. In addition, advances in MR compatible thermal ablation technology allow accurate focal or regional delivery of optimal thermal energy to the biopsy-proved, MRI-detected tumor, utilizing cryoablation, laser ablation, high-intensity focused ultrasound ablation under MR guidance and real-time or near simultaneous monitoring of the ablation zone. Herein we present a contemporary review of MR-guided targeted biopsy techniques of MR-detected lesions as well as MR-guided focal or regional thermal ablative therapies for localized naïve and recurrent cancerous foci of the prostate.     

Contrast-Enhanced Ultrasound for Monitoring Non-surgical Treatments of Uterine Fibroids: A Systematic Review

Non-surgical treatment options for uterine fibroids are uterine artery embolization (UAE), high-intensity focused ultrasound ablation (HIFUA), and percutaneous microwave ablation (PMWA). Magnetic resonance imaging (MRI) is the reference standard imaging method before and after these procedures. Contrast-enhanced ultrasound (CEUS) has been studied as an alternative to MRI for evaluating the fibroids’ characteristics and responses to non-surgical treatments. PubMed, Ovid MEDLINE and Scopus databases were searched for literature published from January 2000 through June 7, 2020, that investigated the application of CEUS as an adjunct to monitor UAE, HIFUA or PMWA in human uterine fibroid treatments. Two independent reviewers analyzed 128 publications, out of which 17 were included. Based on this systematic review, CEUS provides detailed data about fibroid volume and vascularization prior, during and post UAE, and it helps determine the endpoint of the procedure. HIFUA with intra-procedural CEUS has faster volume shrinkage over a shorter time period with less needed energy and provides early detection of residual tissue after HIFUA. CEUS and contrast-enhanced MRI have sufficient agreement to be used interchangeably in the clinic to evaluate the therapeutic effect of PMWA and HIFUA on fibroids.     

Experimental Methods for Improved Spatial Control of Thermal Lesions in Magnetic Resonance-Guided Focused Ultrasound Ablation

Magnetic resonance-guided high-intensity focused ultrasound (MRgHIFU, or MRgFUS) is a hybrid technology that was developed to provide efficient and tolerable thermal ablation of targeted tumors or other pathologic tissues, while preserving the normal surrounding structures. Fast 3-D ablation strategies are feasible with the newly available phased-array HIFU transducers. However, unlike fixed heating sources for interstitial ablation (radiofrequency electrode, microwave applicator, infra-red laser applicator), HIFU uses propagating waves. Therefore, the main challenge is to avoid thermo-acoustical adverse effects, such as energy deposition at reflecting interfaces and thermal drift of the focal lesion toward the near field. We report here our investigations on some novel experimental solutions to solve, or at least to alleviate, these generally known tolerability problems in HIFU-based therapy. Online multiplanar MR thermometry was the main investigational tool extensively used in this study to identify the problems and to assess the efficacy of the tested solutions. We present an improved method to cancel the beam reflection at the exit window (i.e., tissue-to-air interface) by creating a multilayer protection, to dissipate the residual HIFU beam by bulk scattering. This study evaluates selective de-activation of transducer elements to reduce the collateral heating at bone surfaces in the far field, mainly during automatically controlled volumetric ablation. We also explore, using hybrid US/MR simultaneous imaging, the feasibility of using disruptive boiling at the focus, both as a far-field self-shielding technique and as an enhanced ablation strategy (i.e., boiling core controlled HIFU ablation).     

磁共振声辐射力成像技术研究进展

磁共振声辐射力成像（MR-ARFI）将声辐射力与MRI技术相结合,作为一种新兴的高强度聚焦超声（HIFU）治疗监控技术,能够通过探测组织内的微小位移而间接反映组织弹性,具有安全、简便、无需其他激励装置等优点。本文对MR-ARFI的原理、相关序列及其在生物医学方面的应用进展进行综述。     

Diffusion-weighted MRI and liver metastases

Liver metastases are the most frequently encountered malignant liver lesions in the Western countries. Accurate diagnosis of liver metastases is essential for appropriate management of these patients. Multiple imaging modalities, including ultrasound, CT, positron emission tomography, and MRI, are available for the evaluation of patients with suspected or known liver metastases. Contrast-enhanced MRI has a high accuracy for detection and characterization of liver lesions. Additionally, diffusion-weighted MRI (DWI) has been gaining increasing attention. It is a noncontrast technique that is easy to perform, could be incorporated in routine clinical protocols, and has the potential to provide tissue characterization. This article discusses the basic principles of DWI and discusses its emerging role in the detection of liver metastases in patients with extrahepatic malignancies.     

前列腺癌多参数MRI应用现状及进展

MRI是目前公认的前列腺癌最佳影像检查技术。随着影像技术的发展,各种磁共振功能成像技术不断问世并应用于临床,如体素内不相干运动扩散加权成像、扩散张量成像、扩散峰度成像、磁共振波谱、灌注加权成像等,为前列腺癌的早期诊断及临床个体化治疗提供更多的影像学依据。随着研究的深入,多中心、大样本研究的进展及扫描参数的进一步优化,多参数MRI检查将在前列腺癌的早期诊断中发挥越来越重要的作用。     

热消融治疗肿瘤的研究进展

随着现代医学成像技术的快速发展,影像引导热消融技术在越来越多的肿瘤治疗中发挥着不可替代的作用。本文就五种最常见的热消融技术,即射频消融、微波消融、冷冻消融、高强度聚焦超声、激光消融,并对各自的基本原理和优缺点进行综述,以期指导临床热消融技术的进一步推广和应用。     

Thermal Fixation of Swine Liver Tissue after Magnetic Resonance-Guided High-Intensity Focused Ultrasound Ablation

The aim of this study was to investigate experimental conditions for efficient and controlled in vivo liver tissue ablation by magnetic resonance (MR)-guided high-intensity focused ultrasound (HIFU) in a swine model, with the ultimate goal of improving clinical treatment outcome. Histological changes were examined both acutely (four animals) and 1 wk after treatment (five animals). Effects of acoustic power and multiple sonication cycles were investigated. There was good correlation between target size and observed ablation size by thermal dose calculation, post-procedural MR imaging and histopathology, when temperature at the focal point was kept below 90°C. Structural histopathology investigations revealed tissue thermal fixation in ablated regions. In the presence of cavitation, mechanical tissue destruction occurred, resulting in an ablation larger than the target. Complete extra-corporeal MR-guided HIFU ablation in the liver is feasible using high acoustic power. Nearby large vessels were preserved, which makes MR-guided HIFU promising for the ablation of liver tumors adjacent to large veins.     

前列腺中央腺体偶发癌的MRI初步研究

目的探讨前列腺中央腺体偶发癌的常规MRI表现、MR波谱（MRS）代谢特征及其在扩散加权成像（DWI）上的表现。方法对9例行尿道前列腺切除术（TURP）的前列腺中央腺体偶发癌患者做回顾性分析,观察其常规MR表现及其在MRS和DWI上的表现,测量中央腺体的（胆碱＋肌酸）/枸橼酸盐[（Cho＋Cre）/Cit,CC/C]比值、中央腺体表观扩散系数（apparent diffusion coefficient,ADC）值及最小ADC值。结果前列腺中央腺体偶发癌的CC/C值平均为1.04±0.28,范围为0.65～1.45;中央腺体ADC值平均为（1.48±0.18）×10-3mm2/s,范围为（1.16～1.67）×10-3mm2/s;最小ADC值平均为（1.15±0.10）×10-3mm2/s,范围为（0.99～1.25）×10-3mm2/s。结论 MRS和DWI对于前列腺中央腺体偶发癌的诊断具有一定的局限性。-     

MR-guided interventions of the prostate gland.

In recent years MR imaging has played an increasingly important role in the diagnosis and treatment of prostate cancer. MR imaging of the prostate allows a clear delineation of the anatomic structures and prostate tumors when performing interventions such as biopsies, brachytherapy or thermal therapy of the prostate gland. MRI robotic assistance will improve the accuracy of the interventions. Due to the advantages of MR imaging MR-guided prostate interventions will play an increasing role in future.     

Pelvic applications of MR-guided high intensity focused ultrasound

MR-guided high intensity focused ultrasound (MRg HIFU) is a novel method of tissue ablation that incorporates high energy focused ultrasound for tissue heating and necrosis within an MR scanner that provides simultaneous stereotactic tissue targeting and thermometry. To date, MRg HIFU has been used primarily to treat uterine fibroids, but many additional applications in the pelvis are in development. This article reviews the basic technology of MRg HIFU, and the use of MRg HIFU to treat uterine fibroids, adenomyosis, and prostate cancer.     

Diffusion and perfusion MR imaging of the prostate

Conventional anatomic MR imaging has evolved to a superior modality in the evaluation of prostate carcinoma and is now a widely established technique in the detection and staging of this disease, aiding in clinical decision making on treatment and therapy evaluation. Recent improvements in functional MR techniques, such as diffusion-weighted MR imaging and dynamic contrast-enhanced MR imaging, have greatly increased the impact of MR imaging in prostate cancer. The combination of T2-weighted imaging, diffusion-weighted MR imaging, and dynamic contrast-enhanced MR imaging may overcome the limitations of conventional T2-weighted MR imaging of the prostate and may be able accurately to detect, localize, stage, and grade prostate carcinoma and guide biopsies.     

Prostate cancer detection: magnetic resonance (MR) spectroscopic imaging

Magnetic resonance spectroscopic imaging (MRSI) represents a noninvasive technique to extend the diagnostic evaluation of prostatic cancer, beyond the morphologic information provided by MR imaging throughout the detection of cellular metabolites (choline and citrate). MRSI combined with the anatomical information provided by MRI can improve the assessment cancer location and extent within the prostate, extracapsular spread and cancer aggressiveness; both before and after treatment. We review the performance of MRI with MRSI and the role in the detection, localization, staging and management of the patient pre- and posttherapy for prostate cancer.     

Renal complex cysts in adults: contrast-enhanced ultrasound

Contrast-enhanced ultrasound (CEUS) has been proved to be a useful imaging modality to characterize complex renal cysts using the Bosniak classification in a similar way as Computed Tomography (CT). CEUS helps not only in the characterization of complex cysts detected on baseline US but also in the characterization of indeterminate cystic lesions on CT or Magnetic Resonance (MR).     

MRI-powered biomedical devices

Magnetic resonance imaging (MRI) is beneficial for imaging-guided procedures because it provides higher resolution images and better soft tissue contrast than computed tomography (CT), ultrasound, and X-ray. MRI can be used to streamline diagnostics and treatment because it does not require patients to be repositioned between scans of different areas of the body. It is even possible to use MRI to visualize, power, and control medical devices inside the human body to access remote locations and perform minimally invasive procedures. Therefore, MR conditional medical devices have the potential to improve a wide variety of medical procedures; this potential is explored in terms of practical considerations pertaining to clinical applications and the MRI environment. Recent advancements in this field are introduced with a review of clinically relevant research in the areas of interventional tools, endovascular microbots, and closed-loop controlled MRI robots. Challenges related to technology and clinical feasibility are discussed, including MRI based propulsion and control, navigation of medical devices through the human body, clinical adoptability, and regulatory issues. The development of MRI-powered medical devices is an emerging field, but the potential clinical impact of these devices is promising.     

子宫肌瘤超声消融后子宫浆肌层损伤早期MRI影像学特征及临床意义

目的探究子宫肌瘤超声消融后子宫浆肌层损伤早期MRI影像学特征及其临床意义。方法回顾性分析2019年9月~2020年9月在本院接受高强度聚焦超声（HIFU）消融术治疗的150例子宫肌瘤患者的临床资料,所有患者均于手术前后接受MR检查,影像学资料完整。比较手术前后患者的MRI信号改变情况,根据MRI图像特征确定术后患者子宫浆肌层损伤情况,将患者分为损伤组（n=43）和无损伤组（n=107）,观察损伤组患者的MRI形态特征,比较两组患者的超声消融情况及术后不良反应发生情况。结果术前,子宫肌瘤在T1WI上表现为低、等或高信号,在T2WI上表现为低或高低混杂信号、等信号或高信号,增强扫描均显示强化;术后肌瘤T1WI信号增高,T2WI信号变化无明显规律,增强扫描均显示无强化。超声消融后,子宫浆肌层损伤率为28.67%（43/150）,子宫浆肌层损伤的MRI表现为：T2WI序列显示肌瘤周边肌层信号连续,边界清晰;动态增强扫描显示子宫浆肌层呈环状强化,局部灌注缺损,前壁肌瘤的宫浆肌层损伤率最高为31.40%。损伤组的辐照时间、消融总剂量和肌瘤体积消融率均高于无损伤组（P < 0.05）,术后两组患者均出现一定不良反应,且损伤组患者阴道排液发生率高于无损伤组（P < 0.05）。结论子宫肌瘤患者接受HIFU消融术治疗后,早期会出现子宫浆肌层损伤,治疗期间的辐照时间长、消融总剂量及肌瘤体积消融率高会增加患者子宫浆肌层损伤的风险,使患者术后出现不良反应,通过MRI检查可有效评估患者的子宫浆肌层损伤情况。     

磁共振引导聚焦超声:现状与前景

磁共振引导聚焦超声是近年出现的肿瘤热消融技术, 利用超声束可穿过软组织并聚焦于靶区的特点, 使靶区产生高温, 致使组织凝固坏死, 并通过磁共振实时监控治疗范围及靶区内温度变化, 从而保证治疗效果及安全性。这种技术的优势在于完全无创、无须住院治疗、无须麻醉(仅需少量镇静剂)、无离子辐射, 目前已广泛应用于子宫肌瘤/腺肌症、骨肿瘤、前列腺癌、功能性神经疾病、乳腺癌等的临床治疗, 成为国内外研究的热点。     

Hepatocellular nodules in liver cirrhosis: MR evaluation

Liver cirrhosis is a major public health problem worldwide. Common causes of cirrhosis include hepatitis C virus, hepatitis B virus, alcohol consumption, and nonalcoholic steatohepatitis. Cirrhotic livers are characterized by advanced hepatic fibrosis and the development of hepatocellular nodules such as regenerative nodules, dysplastic or neoplastic nodules. Cirrhosis is the strongest predisposing factor for hepatocellular carcinoma (HCC). For example, viral hepatitis is the main risk factor for cirrhosis and is associated with the increased incidence (1%–4% per year) of HCC after development of cirrhosis. Currently, a variety of imaging modalities, including ultrasound (US), computed tomography (CT), magnetic resonance imaging (MRI), and positron-emission tomography (PET) are used in noninvasive evaluation of patients with chronic liver disease and suspected HCC. With technological development of MR scanners, MR imaging has emerged as an important imaging modality for assessing cirrhosis and its complications such as HCC. The recent advance in MR is the introduction of faster sequences which have allowed high-quality imaging of the entire liver with high intrinsic soft-tissue contrast, and also multiphasic dynamic MRI that is essential for the detection and characterization of HCC. In addition, functional MRI including diffusion-weighted MRI, MR elastography, and new MR contrast agent with dual function have been investigated for the clinical utility of detection and characterization of HCCs. In this article, we provide an overview of the state-of-the-art MR imaging techniques being used for noninvasive assessment of hepatocellular nodules including conventional dynamic imaging, liver-specific contrast-enhanced MR imaging, diffusion-weighted imaging, MR spectroscopy, and MR elastography.     

常规MRI在子宫肌瘤超声消融疗效评价及随访中的价值

目的 探讨常规MRI在评价超声消融治疗子宫肌瘤疗效及随访中的价值。方法 回顾性分析158例经超声消融治疗后6个月内接受MR检查的子宫肌瘤患者。所有患者均接受FS TSE T2W序列及增强前后T1W VIBE FS序列成像。分析超声消融后肌瘤的MR平扫图像信号改变,并与增强图像进行比较,观察信号变化规律,计算信号变化区域的体积及其相关性。结果 超声消融治疗后, VIBE FS T1WI上子宫肌瘤高信号区域与增强后所测坏死区域一致,二者间体积差异无统计学意义。单变量分析发现平扫VIBE FS T1WI上高信号区域的体积与增强图像上坏死区域的体积呈高度相关(r=0.99,P<0.001)。FS TSE T2WI可以确定子宫肌瘤的边界、大小。结论 常规MR平扫可准确评价超声消融治疗子宫肌瘤的疗效,T2WI可确定子宫肌瘤的边界、大小,T1WI可准确测量肌瘤坏死区域的体积。     

Image-based 3D modeling and validation of radiofrequency interstitial tumor ablation using a tissue-mimicking breast phantom

Purpose

Minimally invasive treatment of solid cancers, especially in the breast and liver, remains clinically challenging, despite a variety of treatment modalities, including radiofrequency ablation (RFA), microwave ablation or high-intensity focused ultrasound. Each treatment modality has advantages and disadvantages, but all are limited by placement of a probe or US beam in the target tissue for tumor ablation and monitoring. The placement is difficult when the tumor is surrounded by large blood vessels or organs. Patient-specific image-based 3D modeling for thermal ablation simulation was developed to optimize treatment protocols that improve treatment efficacy.

Methods

A tissue-mimicking breast gel phantom was used to develop an image-based 3D computer-aided design (CAD) model for the evaluation of a planned RF ablation. First, the tissue-mimicking gel was cast in a breast mold to create a 3D breast phantom, which contained a simulated solid tumor. Second, the phantom was imaged in a medical MRI scanner using a standard breast imaging MR sequence. Third, the MR images were converted into a 3D CAD model using commercial software (ScanIP, Simpleware), which was input into another commercial package (COMSOL Multiphysics) for RFA simulation and treatment planning using a finite element method (FEM). For validation of the model, the breast phantom was experimentally ablated using a commercial (RITA) RFA electrode and a bipolar needle with an electrosurgical generator (DRE ASG-300). The RFA results obtained by pre-treatment simulation were compared with actual experimental ablation.

Results

A 3D CAD model, created from MR images of the complex breast phantom, was successfully integrated with an RFA electrode to perform FEM ablation simulation. The ablation volumes achieved both in the FEM simulation and the experimental test were equivalent, indicating that patient-specific models can be implemented for pre-treatment planning of solid tumor ablation.

Conclusion

A tissue-mimicking breast gel phantom and its MR images were used to perform FEM 3D modeling and validation by experimental thermal ablation of the tumor. Similar patient-specific models can be created from preoperative images and used to perform finite element analysis to plan radiofrequency ablation. Clinically, the method can be implemented for pre-treatment planning to predict the effect of an individual??s tissue environment on the ablation process, and this may improve the therapeutic efficacy.