DWI predicts uterine fibroid treatment outcome

Researchers from the University Medical Center Utrecht in the Netherlands have used diffusion-weighted MR imaging (DWI) and apparent diffusion coefficient (ADC) mapping to predict the therapeutic outcome for patients receiving volumetric MR-guided HIFU to treat uterine fibroids. With high cellularity and increased vascularity of uterine fibroids identified as predictors for poor MR-HIFU therapeutic efficacy, the team used pre-treatment DWI to provide information on these factors. The researchers treated 30 symptomatic uterine fibroids (in 25 women) with volumetric MR-HIFU, performing DWI prior to treatment and generating ADC maps for each fibroid.

A treatment efficacy index was defined as the ratio of non-perfused volume (NPV) to fibroid volume. The median NPV was 97 cm3, corresponding to 35% of the fibroid volume treated. Treatment was classified as a success if the index was 0.35 or more. The median pre-treatment ADC value of 13 successfully treated fibroids was 1.993 x 10–3 mm2/s, significantly lower than the 2.271 x 10–3 mm2/s seen for the 17 unsuccessfully treated fibroids. Calculating an index for technical success – the ratio of NPV to treatment-cell volume – revealed that median ADC values were again significantly lower in the successfully treated group. Marlijne Ikink, who presented the results, concluded that DWI with ADC mapping may serve as a predictor for MR-HIFU treatment efficacy of symptomatic uterine fibroids, with higher pre-treatment ADC values suggesting lower NPV after ablation.

FUS opens up blood-brain/blood-tumour barriers

The blood-brain barrier prevents effective drug delivery to tumours, and while brain tumours often have leaky blood vessels, heterogeneous permeability and other factors limit the effective delivery of drugs across the tumour vasculature. Researchers from Harvard Medical School and Brigham and Women's Hospital (Boston, MA) previously demonstrated that a single treatment with focused ultrasound (FUS) and liposomal doxorubicin (DOX) can temporarily disrupt the blood-brain barrier, enhance the blood-tumour barrier permeability and slow tumour growth. The team's latest work, presented by Muna Aryal, shows that multiple sessions can effectively inhibit tumour growth and significantly improve survival in a rat glioma model.

Aryal and colleagues divided 29 rats with 9L gliosarcoma tumours into four treatment groups: control, FUS only, DOX only and FUS+DOX. Animals were treated in three weekly sessions and then monitored weekly with MRI. In the control and FUS only groups, tumours grew rapidly and no animal survived for the third treatment. Tumour growth was also rapid in the DOX group, with only two animals receiving the third treatment. In the FUS+DOX group, tumours shrank after the third treatment, and appeared to be completely resolved in five of the eight animals. Median survival was 46 days, significantly longer than seen for the other groups and a 156% improvement from the controls.

Transcranial treatments for neuropathic pain, Parkinson's

Daniel Jeanmonod from the Center for Ultrasound Functional Neurosurgery in Switzerland presented two studies in which MR-guided focused ultrasound was used for incisionless transcranial brain interventions. Thirteen patients with neuropathic pain received medial thalamic FUS thermocoagulations under MR guidance and MR thermometry, with mean peak temperatures of 49–58 °C. Mean absolute targeting accuracies were 0.4, 0.37 and 0.71 mm for mediolateral, anteroposterior and dorsoventral dimensions, respectively. There were no device or procedure related complications and no post-treatment neurological deficits. At three-month or one-year follow-up, patients had a mean pain relief of 54.8% and a mean improvement in visual analogue scale ratings of 36%. Pain relief of 50% or above was seen in 77% of patients.

In the second study, Jeanmonod and co-workers treated eight patients with Parkinson's disease, performing MR-guided subthalamic FUS thermocoagulations, with mean peak temperatures of 52–59 °C. Again, no complications or post-treatment deficits were observed. Mean absolute targeting accuracies were 0.49, 0.4 and 0.56 mm for mediolateral, anteroposterior and dorsoventral dimensions. At three-month follow-up, four patients had a mean improvement in UPDRS (Unified Parkinson's Disease Rating Scale) of 7.6% and mean global symptom relief of 22.5%. Four further patients who received the same treatment but with final sonications repeated 5–6 times, had a 57.1% mean UPDRS improvement and a mean global symptom relief of 47.5%.

Ultrashort echo-time MRI enables bone thermometry

For HIFU treatment of bone tumours, conventional MR thermometry can map the temperature rise in adjacent soft tissue, but cannot directly detect temperature rise in solid tumour mass or the bone itself. Wilson Miller, from the University of Virginia (Charlottesville, VA), explained how combining the thermal-sonication-induced local increase in T1 relaxation times with ultrashort echo time (UTE) pulse sequence techniques can enable direct visualization of the HIFU-induced temperature rise in cortical bone.

Miller and colleagues used a custom UTE pulse sequence on a 3T whole-body MR scanner to image a section of bone during focused ultrasound ablation. Comparing the 3D UTE image (echo time of 0.03 ms) with a conventional fast gradient-echo MRI scan (2.5 ms echo time) showed that the bone marrow was intact and visible in both images, while the surrounding cortical bone was only visible in the UTE image. Image subtraction suppressed the signal from water and fatty marrow and enhanced bone visualization. UTE images recorded before and during FUS application revealed the focal spot as a dark spot inside the bone margin, with the signal decrease due to the T1 increase with temperature. Miller concluded that it is possible to directly detect a thermal MR signal in bone using UTE pulse sequences, and that further development may enable quantitative thermometry in bone.