Magnetic resonance-guided high-intensity ultrasound ablation of the prostate

OBJECTIVES: This paper describes our work in developing techniques and devices for magnetic resonance (MR)-guided high-intensity ultrasound ablation of the prostate and includes review of relevant literature. METHODS: Catheter-based high-intensity ultrasound applicators, in interstitial and transurethral configurations, were developed to be used under MR guidance. Magnetic resonance thermometry and the relevant characteristics and artifacts were evaluated during in vivo thermal ablation of the prostate in 10 animals. Contrast-enhanced MR imaging (MRI) and diffusion-weighted MRI were used to assess tissue damage and compared with histology. RESULTS: During evaluation of these applicators, MR thermometry was used to monitor the temperature distributions in the prostate in real time. Magnetic resonance-derived maximum temperature thresholds of 52 degrees C and thermal dose thresholds of 240 minutes were used to control the extent of treatment and qualitatively correlated well with posttreatment imaging studies and histology. The directional transurethral devices are selective in their ability to target well-defined regions of the prostate gland and can be rotated in discrete steps to conform treatment to prescribed boundaries. The curvilinear applicator is the most precise of these directional techniques. Multisectored transurethral applicators, with dynamic angular control of heating and no rotation requirements, offer a fast and less complex means of treatment with less selective contouring. CONCLUSIONS: The catheter-based ultrasound devices can produce spatially selective regions of thermal destruction in prostate. The MR thermal imaging and thermal dose maps, obtained in multiple slices through the target volume, are useful for controlling therapy delivery (rotation, power levels, duration). Contrast-enhanced T1-weighted MRI and diffusion-weighted imaging are useful tools for assessing treatment.     

MR-guided interventions for prostate cancer

MR imaging is currently the most effective diagnostic imaging tool for visualizing the anatomy and pathology of the prostate gland. Currently, the practicality and cost effectiveness of transrectal ultrasound dominates image guidance for needle-based prostate interventions. Challenges to the integration of diagnostic and interventional MR imaging have included the lack of real-time feed-back, the complexity of the imaging technique, and limited access to the perineum within the geometric constraints of the MR imaging scanner. Two basic strategies have been explored and clinically demonstrated in the literature: (1) coregistration of previously acquired diagnostic MR imaging to interventional TRUS or open scanner MR images, and (2) stereotactic needle interventions within conventional diagnostic scanners using careful patient positioning or the aid of simple manipulators. Currently, researchers are developing techniques that render MR imaging the method of choice for the direct guidance of many procedures. This article focuses on needle-based interventions for prostate cancer, including biopsy, brachytherapy, and thermal therapy With rapid progress in biologic imaging of the prostate gland, the authors believe that MR imaging guidance will play an increasing role in the diagnosis and treatment of prostate cancer.     

Semi-automatic segmentation for prostate interventions

In this paper we report and characterize a semi-automatic prostate segmentation method for prostate brachytherapy. Based on anatomical evidence and requirements of the treatment procedure, a warped and tapered ellipsoid was found suitable as the a-priori 3D shape of the prostate. By transforming the acquired endorectal transverse images of the prostate into ellipses, the shape fitting problem was cast into a convex problem which can be solved efficiently. The average whole gland error between non-overlapping volumes created from manual and semi-automatic contours from 21 patients was 6.63 ± 0.9%. For use in brachytherapy treatment planning, the resulting contours were modified, if deemed necessary, by radiation oncologists prior to treatment. The average whole gland volume error between the volumes computed from semi-automatic contours and those computed from modified contours, from 40 patients, was 5.82 ± 4.15%. The amount of bias in the physicians' delineations when given an initial semi-automatic contour was measured by comparing the volume error between 10 prostate volumes computed from manual contours with those of modified contours. This error was found to be 7.25 ± 0.39% for the whole gland. Automatic contouring reduced subjectivity, as evidenced by a decrease in segmentation inter- and intra-observer variability from 4.65% and 5.95% for manual segmentation to 3.04% and 3.48% for semi-automatic segmentation, respectively. We characterized the performance of the method relative to the reference obtained from manual segmentation by using a novel approach that divides the prostate region into nine sectors. We analyzed each sector independently as the requirements for segmentation accuracy depend on which region of the prostate is considered. The measured segmentation time is 14 ± 1s with an additional 32 ± 14s for initialization. By assuming 1-3 min for modification of the contours, if necessary, a total segmentation time of less than 4 min is required, with no additional time required prior to treatment planning. This compares favorably to the 5-15 min manual segmentation time required for experienced individuals. The method is currently used at the British Columbia Cancer Agency (BCCA) Vancouver Cancer Centre as part of the standard treatment routine in low dose rate prostate brachytherapy and is found to be a fast, consistent and accurate tool for the delineation of the prostate gland in ultrasound images.     

Magnetic resonance imaging--guided breast interventions

The use of breast magnetic resonance imaging (MRI) for screening, diagnosis, staging, and management of breast cancer is rapidly increasing. MRI is highly sensitive for the detection of benign and malignant abnormalities that are occult to physical examination, ultrasound, and mammography. However, the specificity of MRI is moderate. These attributes necessitate methods for MR-guided tissue sampling to determine the histology of MRI detected lesions. This article will review appropriate peer-reviewed data and currently accepted methods for MR-guided tissue sampling. A detailed step-by-step technique for vacuum-assisted MR-guided breast biopsy is included. We also review emerging data for percutaneous and transcutaneous MR-guided breast interventions such as tissue ablation for benign and malignant disease.     

Magnetic resonance-guided biliary drainage in a patient with malignant obstructive jaundice and thrombocytopenia

In a patient suffering from malignant obstructive jaundice and thrombocytopenia, magnetic resonance imaging (MRI) was used to guide percutaneous transhepatic biliary drainage, to avoid blind puncture of the bile ducts using fluoroscopy. The first puncture approach was successful, and an MRI-visible guide wire and drainage catheter were inserted successfully within 35 min. The course after the intervention was uneventful, and the patient's fever and itching improved. MRI guidance facilitated optimal procedure planning and high puncture accuracy.     

Magnetic resonance imaging-guided vascular interventions

Magnetic resonance imaging (MRI), which provides superior soft-tissue imaging and no known harmful effects, has the potential as an alternative modality to guide various medical interventions. This review will focus on MR-guided endovascular interventions and present its current state and future outlook. In the first technical part, enabling technologies such as developments in fast imaging, catheter devices, and visualization techniques are examined. This is followed by a clinical survey that includes proof-of-concept procedures in animals and initial experience in human subjects. In preclinical experiments, MRI has already proven to be valuable. For example, MRI has been used to guide and track targeted cell delivery into or around myocardial infarctions, to guide atrial septal puncture, and to guide the connection of portal and systemic venous circulations. Several investigational MR-guided procedures have already been reported in patients, such as MR-guided cardiac catheterization, invasive imaging of peripheral artery atheromata, selective intraarterial MR angiography, and preliminary angioplasty and stent placement. In addition, MR-assisted transjugular intrahepatic portosystemic shunt procedures in patients have been shown in a novel hybrid double-doughnut x-ray/MRI system. Numerous additional investigational human MR-guided endovascular procedures are now underway in several medical centers around the world. There are also significant hurdles: availability of clinical-grade devices, device-related safety issues, challenges to patient monitoring, and acoustic noise during imaging. The potential of endovascular interventional MRI is great because as a single modality, it combines 3-dimensional anatomic imaging, device localization, hemodynamics, tissue composition, and function.     

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.     

MR to ultrasound registration for image-guided prostate interventions

A deformable registration method is described that enables automatic alignment of magnetic resonance (MR) and 3D transrectal ultrasound (TRUS) images of the prostate gland. The method employs a novel "model-to-image" registration approach in which a deformable model of the gland surface, derived from an MR image, is registered automatically to a TRUS volume by maximising the likelihood of a particular model shape given a voxel-intensity-based feature that represents an estimate of surface normal vectors at the boundary of the gland. The deformation of the surface model is constrained by a patient-specific statistical model of gland deformation, which is trained using data provided by biomechanical simulations. Each simulation predicts the motion of a volumetric finite element mesh due to the random placement of a TRUS probe in the rectum. The use of biomechanical modelling in this way also allows a dense displacement field to be calculated within the prostate, which is then used to non-rigidly warp the MR image to match the TRUS image. Using data acquired from eight patients, and anatomical landmarks to quantify the registration accuracy, the median final RMS target registration error after performing 100 MR-TRUS registrations for each patient was 2.40 mm.     

"MRI Stealth" robot for prostate interventions.

The paper reports an important achievement in MRI instrumentation, a pneumatic, fully actuated robot located within the scanner alongside the patient and operating under remote control based on the images. Previous MRI robots commonly used piezoelectric actuation limiting their compatibility. Pneumatics is an ideal choice for MRI compatibility because it is decoupled from electromagnetism, but pneumatic actuators were hardly controllable. This achievement was possible due to a recent technology breakthrough, the invention of a new type of pneumatic motor, PneuStep 1, designed for the robot reported here with uncompromised MRI compatibility, high-precision, and medical safety. MrBot is one of the "MRI stealth" robots today (the second is described in this issue by Zangos et al.). Both of these systems are also multi-imager compatible, being able to operate with the imager of choice or cross-imaging modalities. For MRI compatibility the robot is exclusively constructed of nonmagnetic and dielectric materials such as plastics, ceramics, crystals, rubbers and is electricity free. Light-based encoding is used for feedback, so that all electric components are distally located outside the imager's room. MRI robots are modern, digital medical instruments in line with advanced imaging equipment and methods. These allow for accessing patients within closed bore scanners and performing interventions under direct (in scanner) imaging feedback. MRI robots could allow e.g. to biopsy small lesions imaged with cutting edge cancer imaging methods, or precisely deploy localized therapy at cancer foci. Our robot is the first to show the feasibility of fully automated in-scanner interventions. It is customized for the prostate and operates transperineally for needle interventions. It can accommodate various needle drivers for different percutaneous procedures such as biopsy, thermal ablations, or brachytherapy. The first needle driver is customized for fully automated low-dose radiation seed brachytherapy. This paper gives an introduction to the challenges of MRI robot compatibility and presents the solutions adopted in making the MrBot. Its multi-imager compatibility and other preclinical tests are included. The robot shows the technical feasibility of MRI-guided prostate interventions, yet its clinical utility is still to be determined.     

Magnetic resonance imaging of the prostate and bladder

Prostate carcinoma is the most common cancer in men and the second most lethal malignancy among the American male population. Nevertheless, it is potentially curable if detected early and treated appropriately. Treatment options vary depending on the extent (stage) of the cancer. MRI has no role as a screening method for prostatic carcinoma because it is expensive, time consuming, and unable to differentiate benign from malignant disease, but it can detect early prostatic cancers in patients with known tumor and can accurately stage these tumors. MRI is becoming the imaging modality of choice for local staging of prostate cancer and is rapidly replacing CT and ultrasonography for this purpose. Treatment protocols for bladder carcinoma also depend on the stage of the tumor. Clinical staging of bladder cancer has been limited. MRI is as good as or better than CT in bladder tumor staging when extravesical tumor involvement is present. MRI also has the potential to become useful in determining the depth of wall invasion in tumors confined to the bladder.     

New clinical applications of magnetic resonance-guided focused ultrasound

Magnetic resonance-guided ultrasound delivers destructive energy into deep body structures with great accuracy and repeatability with an excellent safety profile. The use of this technology for the treatment of uterine fibroids is already becoming widespread. This article reviews the further areas of magnetic resonance-guided focused ultrasound application that are evolving and how they will be applied to other parts of the body.     

护理干预对TURP术后出血的影响

目的探讨护理干预措施对TURP患者术后出血的影响。方法 171例TURP患者,其中观察组86例,对照组85例(回顾分析资料),对他们的术后出血情况进行临床分析,对照组进行常规治疗、护理,观察组在常规治疗、护理的基础上实施系统的护理干预。结果观察组术后近期出血情况,明显低于对照组(P<0.05),术后继发出血情况也明显少于对照组。结论通过对TURP患者术后近期和远期出血的相关影响因素进行护理干预,患者出血量明显减少,减轻患者痛苦,促进康复。     

护理干预对前列腺电切除术后膀胱痉挛的影响

经尿道前列腺电切除术(TURP)是治疗良性前列腺增生(BPH)的金标准,疗效显著,治愈率高,虽然手术创伤小,但术后留置导尿[1]、造瘘管刺激、术后膀胱冲洗以及术后病人主观焦虑情绪等因素仍存在,膀胱痉挛成为TURP术后最常见的并发症之一,病人痛苦较大.2006年1月-2006年12月,我科对87例行TURP病人除进行常规护理外,加强了对病人认知、情绪、行为的护理干预,取得了较好的效果.现报道如下.     

Clinical use of a nonferromagnetic needle for magnetic resonance-guided biopsy

Five patients who had liver lesions detected by magnetic resonance (MR) and/or computed tomography (CT) were biopsied using MR guidance with a specially designed nonferromagnetic needle. The 20-gauge needle was constructed from Type 316 stainless steel in order to maximize needle visibility and minimize needle-tip artifact. In all cases adequate tissue was obtained for diagnosis and no side effects were observed during the biopsy or on clinical follow-up despite the fact that the needle was within the patient in MR for an average of 30 min.     

Acoustic characterization of Thiel liver for magnetic resonance-guided focused ultrasound treatment

Background: The purpose of this work was to measure the essential acoustic parameters, i.e., acoustic impedance, reflection coefficient, attenuation coefficient, of Thiel embalmed human and animal liver. The Thiel embalmed tissue can be a promising, pre-clinical model to study liver treatment with Magnetic Resonance-guided Focused Ultrasound (MRgFUS).

Material and methods: Using a single-element transducer and the contact pulse-echo method, the acoustic parameters, i.e., acoustic impedance, reflection coefficient and attenuation coefficient of Thiel embalmed human and animal liver were measured.

Results: The Thiel embalmed livers had higher impedance, similar reflection and lower attenuation compared to the fresh tissue.

Conclusions: Embalming liver with Thiel fluid affects its acoustic properties. During MRgFUS sonication of a Thiel organ, more focused ultrasound (FUS) will be backscattered by the organ, and higher acoustic powers are required to reach coagulation levels (temperatures >56?°C).     

Preclinical evaluation of an MRI-compatible pneumatic robot for angulated needle placement in transperineal prostate interventions

Purpose

To evaluate the targeting accuracy of a small profile MRI-compatible pneumatic robot for needle placement that can angulate a needle insertion path into a large accessible target volume.

Methods

We extended our MRI-compatible pneumatic robot for needle placement to utilize its four degrees-of-freedom (4-DOF) mechanism with two parallel triangular structures and support transperineal prostate biopsies in a closed-bore magnetic resonance imaging (MRI) scanner. The robot is designed to guide a needle toward a lesion so that a radiologist can manually insert it in the bore. The robot is integrated with navigation software that allows an operator to plan angulated needle insertion by selecting a target and an entry point. The targeting error was evaluated while the angle between the needle insertion path and the static magnetic field was between ?5.7° and 5.7° horizontally and between ?5.7° and 4.3° vertically in the MRI scanner after sterilizing and draping the device.

Results

The robot positioned the needle for angulated insertion as specified on the navigation software with overall targeting error of 0.8 ± 0.5mm along the horizontal axis and 0.8 ± 0.8mm along the vertical axis. The two-dimensional root-mean-square targeting error on the axial slices as containing the targets was 1.4mm.

Conclusions

Our preclinical evaluation demonstrated that the MRI-compatible pneumatic robot for needle placement with the capability to angulate the needle insertion path provides targeting accuracy feasible for clinical MRI-guided prostate interventions. The clinical feasibility has to be established in a clinical study.     

Nursing interventions to improve the health of men with prostate cancer undergoing radiotherapy: a review.

The aim of this study was to investigate what nurses do to improve the health of men who are receiving radiotherapy treatment due to prostate cancer. The method was a literature review using a systematic approach. The Cochrane Library, Medline and CINAHL databases were used in a search that covered the period from January 1994 to April 2006. The screening of 200 abstracts resulted in 14 articles corresponding to the research question, which were assessed according to scientific quality. Two independent reviewers performed the screening and quality assessment process using specific protocols. Two themes emerged: nurse-led care related to radiotherapy treatment and patients' experiences of radiotherapy treatment. The results show that there is strong scientific support for nurse-led follow-up care aimed at assisting patients by means of providing information on how to manage side effects (evidence grade A). In addition, there is moderate scientific support for the need to ensure that this information is structured, objective and concrete and that it can be provided by means of audiotapes or over the phone (evidence grade B) as well as weak scientific support for reporting patients' experiences of radiotherapy treatment (evidence grade C).     

氯化锰标记前列腺癌细胞株的体外MRI研究

目的 初步探索使用氯化锰（MnCl2）标记前列腺癌细胞株（PC-3）行体外MRI的可行性和安全性.方法 将PC-3进行复苏、培养和扩增.在细胞培养箱中,PC-3与8组含不同MnCl2浓度的F-12 HAM＇S培养基共同培养1h,收集已标记的PC-3并行MRI.另对不同细胞数量级和不同时间点的MnCl2标记的PC-3行MRI.用含维拉帕米的培养基培养MnCl2标记的PC-3 4 h,在不同时间点取标记后的PC-3行MRI.用WST-8法测定氯化锰标记的PC-3活性.结果 MnCl2标记的PC-3在T1WI显示为高信号,其信号强度与未标记的PC-3形成明显差异（P＜0.01）,以1.0 mmol /L MnCl2为标记浓度时信号强度最强.1.0mmol/L MnCl2标记的PC-3在细胞数量为0.5×106时可呈高信号.在体外培养的条件下,标记后24 h的PC-3信号强度明显下降,标记后72 h基本恢复至未标记的PC-3信号强度水平.维拉帕米可延长MnCl2标记的PC-3有效成像时间至72 h.标记后4 h,除0.1 mmol/L MnCl2对PC-3的活性没有影响（P ＞ 0.05）外,其余各浓度组（＞ 0.1mmol/L）的MnCl2对PC-3的活性均有不同程度的影响（P ＜ 0.05）;标记后24h,0.5 ～ 1.0 mmol/L MnCl2对细胞的活性影响不明显（P ＞ 0.05）.结论 MnCl2可以有效标记PC-3,并能在T1WI以高信号成像且具有一定灵敏度.在浓度低于或等于1.0 mmol/L时,标记PC-3有一定的安全性,但标记维持时间较短.钙离子通道阻滞剂（维拉帕米）可适当延长PC-3的MnCl2标记维持时间.