Prolonged heating in nontargeted tissue during MR‐guided focused ultrasound of bone tumors

A review of high-intensity focused ultrasound as a novel and non-invasive interventional radiology technique

High-intensity focused ultrasound (HIFU) is a non-invasive interventional radiology technology, which has been generally accepted in clinical practice for the treatment of benign and malignant tumors. HIFU can cause targeted tissue coagulative necrosis and protein denaturation by thermal or non-thermal effects, guided by diagnostic ultrasound or magnetic resonance imaging, without destruction of the normal adjacent tissue, under sedation or general anesthesia. HIFU has become an important alternative to standard treatments of solid tumors, including surgery, radiation, and medications. The aim of this review is to describe the development, principle, devices, and clinical applications of HIFU.

Musculoskeletal Applications of Magnetic Resonance-Guided Focused Ultrasound

Magnetic resonance-guided focused ultrasound (MRgFUS) is a novel noninvasive therapy that uses focused sound energy to thermally ablate focal pathology within the body. In the United States, MRgFUS is approved by the Food and Drug Administration for the treatment of uterine fibroids, palliation of painful bone metastases, and thalamotomy for the treatment of essential tremor. However, it has also demonstrated utility for the treatment of a wide range of additional musculoskeletal (MSK) conditions that currently are treated as off-label indications. Advantages of the technology include the lack of ionizing radiation, the completely noninvasive technique, and the precise targeting that offer unprecedented control of the delivery of the thermal dose, as well as real-time monitoring capability with MR thermometry. In this review, we describe the most common MSK applications of MRgFUS: palliation of bone metastases, treatment of osteoid osteomas, desmoid tumors, facet arthropathy, and other developing indications.

Interleaved water and fat MR thermometry for monitoring high intensity focused ultrasound ablation of bone lesions

PURPOSE

To demonstrate that interleaved MR thermometry can monitor temperature in water and fat with adequate temporal resolution. This is relevant for high intensity focused uUltrasounds (HIFU) treatment of bone lesions, which are often found near aqueous tissues, as muscle, or embedded in adipose tissues, as subcutaneous fat and bone marrow.

METHODS

Proton resonance frequency shift (PRFS)-based thermometry scans and T1 -based 2D variable flip angle (2D-VFA) thermometry scans were acquired alternatingly over time. Temperature in water was monitored using PRFS thermometry, and in fat by 2D-VFA thermometry with slice profile effect correction. The feasibility of interleaved water/fat temperature monitoring was studied ex vivo in porcine bone during MR-HIFU sonication. Precision and stability of measurements in vivo were evaluated in a healthy volunteer under non-heating conditions.

RESULTS

The method allowed observing temperature change over time in muscle and fat, including bone marrow, during MR-HIFU sonication, with a temporal resolution of 6.1 s. In vivo, the apparent temperature change was stable on the time scale of the experiment: In 7 min the systematic drift was <0.042°C/min in muscle (PRFS after drift correction) and <0.096°C/min in bone marrow (2D-VFA). The SD of the temperature change averaged over time was 0.98°C (PRFS) and 2.7°C (2D-VFA).

CONCLUSIONS

Interleaved MR thermometry allows temperature measurements in water and fat with a temporal resolution high enough for monitoring HIFU ablation. Specifically, combined fat and water thermometry provides uninterrupted information on temperature changes in tissue close to the bone cortex.

MRI-Guided Focused Ultrasound of Osseous Metastases: Treatment Parameters Associated With Successful Pain Reduction

BACKGROUND

A phase 3 multicenter trial demonstrated that magnetic resonance imaging (MRI)-guided focused ultrasound (US) is a safe, noninvasive treatment that alleviated pain from bone metastases. However, outcomes varied among institutions (from 0%-100% treatment success).

PURPOSE

The aim of this study was to identify patient selection, technical treatment, and imaging parameters that predict successful pain relief of osseous metastases after MRI-guided focused US.

MATERIALS AND METHODS

This was a secondary analysis of a phase 3 clinical study that included participants who received MRI-guided focused US treatment for painful osseous metastases. Noncontrast CT was obtained before treatment. T2-weighted and T1-weighted postcontrast MRIs at 1.5 T or 3 T were obtained before, at the time of, and at 3 months after treatment. Numerical Rating Scale pain scores and morphine equivalent daily dose data were obtained over a 3-month follow-up period. At the 3-month endpoint, participants were categorized as pain relief responders or nonresponders based on Numerical Rating Scale and morphine equivalent daily dose data. Demographics, technical parameters, and imaging features associated with pain relief were determined using stepwise univariable and multivariable models. Responder rates between the subgroup of participants with all predictive parameters and that with none of the parameters were compared using Fisher exact test.

RESULTS

The analysis included 99 participants (mean age, 59 ± 14 years; 56 women). The 3 variables that predicted successful pain relief were energy density on the bone surface (EDBS) (P = 0.001), the presence of postprocedural periosteal devascularization (black band, BB+) (P = 0.005), and female sex (P = 0.02). The subgroup of participants with BB+ and EDBS greater than 5 J/mm2 had a larger decrease in mean pain score (5.2; 95% confidence interval, 4.6-5.8) compared with those without (BB-, EDBS ≤ 5 J/mm2) (1.1; 95% confidence interval, 0.8-3.0; P < 0.001). Participants with all 3 predictive variables had a pain relief responder rate of 93% compared with 0% in participants having none of the predictive variables (P < 0.001).

CONCLUSIONS

High EDBS during treatment, postprocedural periosteal devascularization around the tumor site (BB+), and female sex increased the likelihood of pain relief after MRI-guided focused US of osseous metastasis.

Diastasis recti abdominis in adult women based on abdominal computed tomography imaging: Prevalence, risk factors and its impact on life

AIMS AND OBJECTIVES

This study aimed to obtain the incidence of diastasis recti abdominis (DRA) and analyse possible risk factors in adult females. Moreover, the relationships between DRA and lower back pain, pelvic floor function and quality of life were also analysed.

BACKGROUND

Diastasis recti abdominis is a separation of the abdominal muscles at the linea alba. Currently, studies on the prevalence rates, risk factors and consequences of DRA are varied. In particular, reports on DRA among adult women are lacking.

DESIGN

A one-sample questionnaire study design is used following the STROBE checklist.

METHODS

The inter-rectus distance was measured by computed tomography in 644 women. Custom questionnaires, the Oswestry Disability Index, The International Consultation on Incontinence Questionnaire-Urinary Incontinence Short Form and the Medical Outcomes Study 36-Item Short Form Health Survey (SF-36) were used to investigate personal information, the subjects' back pain, pelvic floor function and quality of life, respectively.

RESULTS

The incidence of DRA was 28.4%. Age, the number of pregnancies, BMI and diabetes were influencing factors for DRA. After age stratification, pregnancy and diabetes were found to be risk factors for DRA in young women, and obesity and diabetes were risk factors for DRA in older women. This study showed that the association between DRA and low back pain was highly significant.

CONCLUSIONS

Diastasis recti abdominis is common in adult women. Avoiding multiple pregnancies, preventing diabetes and controlling weight may prevent DRA, which may be beneficial for decreasing low back pain in women.

RELEVANCE TO CLINICAL PRACTICE

The findings have important implications for the health of adult women which can provide the basis for appropriate nursing implementation for DRA patients. The application of specific prevention and intervention measures for the risk factors may reduce the severity of low back pain.