Radiofrequency ablation for the treatment of a presumed enchondroma in the flat bones of the pelvis.

Herein, a 30-year-old Caucasian female who presented with a persistent pain in the right pelvic region due to an enchondroma and treated with RF ablation is described. An initial MRI of the pelvis revealed a well-circumscribed lesion in the right inferior ischiopubic ramus with a maximum diameter of 9.5 mm. The final diagnosis was established by a percutaneous CT-guided bone biopsy, which excluded malignancy and revealed an enchondroma. About a month after the biopsy, a percutaneous radiofrequency ablation (RFA) of the lesion was performed. The symptoms resolved completely gradually 2 months after the treatment and a follow-up imaging with MRI showed complete resolution of the pathological enhancement indicating necrosis of the lesion. RFA has not been previously reported as a treatment option of enchondromas found in flat bones of the pelvis and could be a safe alternative minimally invasive treatment option in such cases, avoiding major operations.

MR relaxation times of agar-based tissue-mimicking phantoms.

Agar gels were previously proven capable of accurately replicating the acoustical and thermal properties of real tissue and widely used for the construction of tissue-mimicking phantoms (TMPs) for focused ultrasound (FUS) applications. Given the current popularity of magnetic resonance-guided FUS (MRgFUS), we have investigated the MR relaxation times T1 and T2 of different mixtures of agar-based phantoms. Nine TMPs were constructed containing agar as the gelling agent and various concentrations of silicon dioxide and evaporated milk. An agar-based phantom doped with wood powder was also evaluated. A series of MR images were acquired in a 1.5 T scanner for T1 and T2 mapping. T2 was predominantly affected by varying agar concentrations. A trend toward decreasing T1 with an increasing concentration of evaporated milk was observed. The addition of silicon dioxide decreased both relaxation times of pure agar gels. The proposed phantoms have great potential for use with the continuously emerging MRgFUS technology. The MR relaxation times of several body tissues can be mimicked by adjusting the concentration of ingredients, thus enabling more accurate and realistic MRgFUS studies.

PET/CT imaging of prostate cancer in the era of small molecule prostate specific membrane antigen targeted tracers.

Staging and restaging of prostate cancer is crucial for treatment planning and prognosis. Accurate localization is of high relevance for a tailor-made therapy and an early detection of unknown metastatic spread can lead to a survival benefit. Evidence based guidelines that are currently in use were established using data from conventional imaging (such as magnetic resonance imaging (MRI), computed tomography (CT) and bone scintigraphy). Prostate-specific membrane antigen (PSMA) positron emission tomography (PET) is rapidly evolving with promising results. However, up to now there is little consensus about the usefulness of this method, especially since different guidelines are "biased" depending on the association that shapes them. Firstly, little data exists on the staging of low risk tumors and probably PSMA PET/CT should be avoided in this setup for most patients. On the other hand, it has been recently proven that PSMA PET/CT can replace CT and bone scintigraphy (combined) in staging of advanced prostate cancer. Furthermore, the examination gained general acceptance through its excellent performance in biochemical recurrence, both for castration naïve and castration resistant tumors, and should be implemented where available. It is undisputed that PSMA PET/CT provides a more accurate picture of prostate cancer patients and can lead to both upstaging and downstaging, thus affecting therapeutic management. Though it is not clear yet if the more accurate staging will lead to better therapeutic decisions and improve patient outcomes, PSMA PET/CT appears as the next imaging standard for prostate cancer for the years to come.

Osteoid osteoma of the scaphoid bone associated with flexor carpi radialis calcific tendinitis and treated with CT-guided RF ablation.

Osteoid osteomas of the wrist are relatively rare and the diagnosis is challenging due to atypical clinical features. We describe a case of an osteoid osteoma of the scaphoid bone associated with calcific tendinitis of the adjacent flexor carpi radialis tendon and periarticular soft tissue calcifications in a 21-year-old man presenting with radial-sided wrist pain. The lesion was successfully treated with CT-guided RF ablation. To our knowledge, this is the first description of an osteoid osteoma of the wrist associated with calcific tendinitis and periarthritis. In addition, we discuss the technical details and difficulties of CT-guided RF ablation of scaphoid osteoid osteomas.

Spinal osteoid osteoma progressed to osteoblastoma with paraspinal soft tissue mass: a unique presentation.

Osteoid osteoma and osteoblastoma are rare benign bone-forming tumors with very similar histological features. They are nowadays considered as two distinct entities. Progression of an osteoid osteoma to osteoblastoma is considered very rare with only a few cases reported in the literature. Herein we describe a case of an osteoid osteoma of the thoracic spine in a 29-year-old woman that was initially treated conservatively and progressed to osteoblastoma 5 years following the initial diagnosis. Imaging revealed an increase in the size of the spinal lesion that was surrounded by extensive paraspinal abnormal soft tissue that raised suspicion for sarcomatous transformation. The final diagnosis was established by CT-guided biopsy of both the bone lesion and the paraspinal soft tissue, which excluded malignancy and revealed an osteoblastoma surrounded by plasma cell-rich chronic inflammation. The patient then underwent wide surgical excision of the lesion and paraspinal soft tissue component that confirmed the diagnosis. Follow-up with MRI over the next 12 months was unremarkable, with no signs of recurrence or spinal instability. This unique presentation of an osteoblastoma has not been previously described. This case also demonstrates the importance of follow-up of osteoid osteomas that are treated conservatively.

MRI compatibility testing of commercial high intensity focused ultrasound transducers.

PURPOSE: The study aimed to compare the performance of eight commercially available single-element High Intensity Focused Ultrasound (HIFU) transducers in terms of Magnetic Resonance Imaging (MRI) compatibility. METHODS: Imaging of an agar-based MRI phantom was performed in a 3 T MRI scanner utilizing T2-Weighted Fast Spin Echo (FSE) and Fast low angle shot (FLASH) sequences, which are typically employed for high resolution anatomical imaging and thermometry, respectively. Reference magnitude and phase images of the phantom were compared with images acquired in the presence of each transducer in terms of the signal to noise ratio (SNR), introduced artifacts, and overall image quality. RESULTS: The degree of observed artifacts highly differed among the various transducers. The transducer whose backing material included magnetic impurities showed poor performance in the MRI, introducing significant susceptibility artifacts such as geometric distortions and signal void bands. Additionally, it caused the most significant SNR drop. Other transducers were shown to exhibit high level of MRI compatibility as the resulting images closely resembled the reference images with minimal to no apparent artifacts and comparable SNR values. CONCLUSIONS: The study findings may facilitate researchers to select the most suitable transducer for their research, simultaneously avoiding unnecessary testing. The study further provides useful design considerations for MRI compatible transducers.

Tumor phantom model for MRI-guided focused ultrasound ablation studies.

BACKGROUND: The persistent development of focused ultrasound (FUS) thermal therapy in the context of oncology creates the need for tissue-mimicking tumor phantom models for early-stage experimentation and evaluation of relevant systems and protocols. PURPOSE: This study presents the development and evaluation of a tumor-bearing tissue phantom model for testing magnetic resonance imaging (MRI)-guided FUS (MRgFUS) ablation protocols and equipment based on MR thermometry. METHODS: Normal tissue was mimicked by a pure agar gel, while the tumor simulator was differentiated from the surrounding material by including silicon dioxide. The phantom was characterized in terms of acoustic, thermal, and MRI properties. US, MRI, and computed tomography (CT) images of the phantom were acquired to assess the contrast between the two compartments. The phantom's response to thermal heating was investigated by performing high power sonications with a 2.4 MHz single element spherically focused ultrasonic transducer in a 3T MRI scanner. RESULTS: The estimated phantom properties fall within the range of literature-reported values of soft tissues. The inclusion of silicon dioxide in the tumor material offered excellent tumor visualization in US, MRI, and CT. MR thermometry revealed temperature elevations in the phantom to ablation levels and clear evidence of larger heat accumulation within the tumor owing to the inclusion of silicon dioxide. CONCLUSION: Overall, the study findings suggest that the proposed tumor phantom model constitutes a simple and inexpensive tool for preclinical MRgFUS ablation studies, and potentially other image-guided thermal ablation applications upon minimal modifications.

Phantom-based assessment of motion and needle targeting accuracy of robotic devices for magnetic resonance imaging-guided needle biopsy.

BACKGROUND: The current study proposes simple methods for assessing the performance of robotic devices intended for Magnetic Resonance Imaging (MRI)-guided needle biopsy. METHODS: In-house made agar-based breast phantoms containing biopsy targets served as the main tool in the evaluation process of an MRI compatible positioning device comprising a needle navigator. The motion accuracy of mechanical stages was assessed by calliper measurements. Laboratory evaluation of needle targeting included a repeatability phantom test and a laser-based method. The accuracy and repeatability of needle targeting was also assessed by MRI. RESULTS: The maximum error of linear motion for steps up to 10 mm was 0.1 mm. Needle navigation relative to the phantom and alignment with the various biopsy targets were performed successfully in both the laboratory and MRI settings. The proposed biopsy phantoms offered tissue-like signal in MRI and good haptic feedback during needle insertion. CONCLUSIONS: The proposed methods could be valuable in the process of validating the accuracy of MRI-guided biopsy robotic devices in both laboratory and real environments.

Challenges regarding MR compatibility of an MRgFUS robotic system.

Numerous challenges are faced when employing Magnetic Resonance guided Focused Ultrasound (MRgFUS) hardware in the Magnetic Resonance Imaging (MRI) setting. The current study aimed to provide insights on this topic through a series of experiments performed in the framework of evaluating the MRI compatibility of an MRgFUS robotic device. All experiments were performed in a 1.5 T MRI scanner. The main metric for MRI compatibility assessment was the signal to noise ratio (SNR). Measurements were carried out in a tissue mimicking phantom and freshly excised pork tissue under various activation states of the system. In the effort to minimize magnetic interference and image distortion, various set-up parameters were examined. Significant SNR degradation and image distortion occurred when the FUS transducer was activated mainly owing to FUS-induced target and coil vibrations and was getting worse as the output power was increased. Proper design and stable positioning of the imaged phantom play a critical role in reducing these vibrations. Moreover, isolation of the phantom from the imaging coil was proven essential for avoiding FUS-induced vibrations from being transferred to the coil during sonication and resulted in a more than 3-fold increase in SNR. The use of a multi-channel coil increased the SNR by up to 50 % compared to a single-channel coil. Placement of the electronics outside the coil detection area increased the SNR by about 65 %. A similar SNR improvement was observed when the encoders' counting pulses were deactivated. Overall, this study raises awareness about major challenges regarding operation of an MRgFUS system in the MRI environment and proposes simple measures that could mitigate the impact of noise sources so that the monitoring value of MR imaging in FUS applications is not compromised.

Simple methods to test the accuracy of MRgFUS robotic systems.

BACKGROUND: Robotic-assisted diagnostic and therapeutic modalities require a highly accurate performance to be certified for clinical application. In this paper, three simple methods for assessing the accuracy of motion of magnetic resonance-guided focused ultrasound (MRgFUS) robotic systems are presented. METHODS: The accuracy of motion of a 4 degrees of freedom robotic system intended for preclinical use of MRgFUS was evaluated by calliper-based and magnetic resonance imaging (MRI) methods, as well as visually by performing multiple ablations on a plastic film. RESULTS: The benchtop results confirmed a highly accurate motion in all axes of operation. The spatial positioning errors estimated by MRI evaluation were defined by the size of the imaging pixels. Lesions arrangement in discrete and overlapping patterns confirmed satisfactory alignment of motion trajectories. CONCLUSIONS: We believe the methods presented here should serve as a standard for evaluating the accuracy of motion of MRgFUS robotic systems.

MRI-guided frameless biopsy robotic system with the inclusion of unfocused ultrasound transducer for brain cancer ablation.

BACKGROUND: A magnetic resonance image (MRI) guided robotic system dedicated for brain biopsy was developed. The robotic system carries a biopsy needle and a small rectangular unfocused, single element, planar ultrasonic transducer which can be potentially utilized to ablate small and localized brain cancer. MATERIALS AND METHODS: The robotic device includes six computer-controlled axes. An agar-based phantom was developed which included an olive that mimics brain target. A rectangular ultrasonic transducer operated at 4 MHz was used. RESULTS: The functionality of the robotic system was assessed by means of ultrasound imaging, MRI imaging, and MR thermometry, demonstrating effective targeting. The heating capabilities of the ultrasonic transducer were also evaluated. CONCLUSIONS: A functional MRI-guided robotic system was produced which can perform frameless brain biopsy. In the future, if a tumour is proven malignant, the needle can be pulled-out and a small ultrasonic transducer can be inserted to ablate the tumour.

MRI-compatible breast/rib phantom for evaluating ultrasonic thermal exposures.

INTRODUCTION: The target of this study was the development of a magnetic resonance imaging (MRI) compatible breast phantom for focused ultrasound which includes plastic (ABS) ribs. The objective of the current study was the evaluation of a focused ultrasound procedure using the proposed phantom that eliminates rib heating. MATERIAL AND METHODS: The proposed phantom was evaluated using two different focused ultrasound exposures. The surrounding breast tissue was mimicked using an agar-silica-evaporation milk gel (2% w/v - 2% w/v - 40% v/v). RESULTS: The attenuation of the ABS was similar to that of ribs. MR thermometry of focused ultrasound exposures were acquired using the breast/rib phantom. In one exposure focused ultrasound was applied with far-field targeting of the ribs. In the other exposure, the transducer was positioned laterally, thus avoiding exposure of the rib to focused ultrasound. CONCLUSIONS: Due to growing interest in using MRI guided focused ultrasound (MRgFUS) for patients with breast cancer, the proposed breast/rib phantom can be utilized as a very useful tool for evaluating ultrasonic protocols.

MRI guided focused ultrasound robotic system for animal experiments.

BACKGROUND: In this paper an MRI-guided focused ultrasound (MRgFUS) robotic system was developed that can be used for conducting experiments in small animals.The target for this robotic system regarding motion was to move a therapeutic ultrasound transducer in two Cartesian axes. METHODS: A single element spherically focused transducer of 3 cm diameter, focusing at 7 cm and operating at 0.4 MHz was used. The positioning device incorporates only MRI compatible materials. The propagation of ultrasound is a bottom to top approach. The 2-D positioning device is controlled by custom-made software and a custom-made electronic system which controls the two piezoelectric motors. RESULTS: The system was tested successfully in agar/silica/evaporated milk phantom for various tasks (robot motion, MR compatibility, and MR thermometry). The robotic system is capable of moving the focused ultrasound transducer to perform MR-guided focused ultrasound experiments in small animals. CONCLUSIONS: This system has the potential to be deployed as a cost effective solution for performing experiments in small animals.

MRI-compatible bone phantom for evaluating ultrasonic thermal exposures.

OBJECTIVE: The goal of the proposed study was the development of a magnetic resonance imaging (MRI) compatible bone phantom suitable for evaluating focused ultrasound protocols. MATERIALS AND METHODS: High resolution CT images were used to segment femur bone. The segmented model was manufactured with (Acrylonitrile Butadiene Styrene) ABS plastic using a 3-D printer. The surrounding skeletal muscle tissue was mimicked using an agar-silica-evaporated milk gel (2% w/v-2% w/v-40% v/v). MR thermometry was used to evaluate the exposures of the bone phantom to focused ultrasound. RESULTS: The estimated agar-silica-evaporated milk gel's T1 and T2 relaxation times in a 1.5T magnetic field were 776ms and 66ms respectively. MR thermometry maps indicated increased temperature adjacent to the bone, which was also shown in situations of real bone/tissue interfaces. CONCLUSION: Due to growing interest of using MRI guided Focused Ultrasound Surgery (MRgFUS) in palliating bone cancer patients at terminal stages of the disease, the proposed bone phantom can be utilized as a very useful tool for evaluating ultrasonic protocols, thus minimizing the need for animal models. The estimated temperature measured and its distribution near the bone phantom/agar interface which was similar to temperatures recorded in real bone ablation with FUS, confirmed the phantom's functionality.