Percutaneous MR Imaging– guided Radiofrequency Interstitial Thermal Ablation of Tongue Base in Porcine Models: Implications for Obstructive Sleep Apnea Syndrome

Partial Glossectomy Combined With Radiofrequency Ablation for Macroglossia in Beckwith-Wiedemann Syndrome

OBJECTIVE

As the most common feature of Beckwith-Wiedemann syndrome (BWS), macroglossia may influence the quality of life, maxillofacial growth, and speech development of children. The retrospective study aimed to investigate the therapeutic effect of partial glossectomy combined with radiofrequency ablation (RFA) for macroglossia patients in BWS.

METHODS

A retrospective study was conducted in BWS-derived macroglossia patients who underwent partial glossectomy combined with RFA from May 2019 to January 2021. In total, 35 patients consisting of 17 males and 18 females met the inclusion criteria and underwent surgery by the same plastic surgeon. Demographic characteristics, BWS features, operation details, preoperative and postoperative outcomes, satisfaction evaluations, and subgroup analysis were collected and assessed.

RESULTS

Of the 35 patients involved, the average age at the time of surgery was 14.05±8.08 months, and the average surgery duration was 48.17±6.72 minutes. Only 1 patient suffered ventral tongue wound dehiscence, and the rest of the patients did not develop any other complications. The severity and frequency of tongue protrusion, drooling, snoring, and feeding difficulty were significantly ameliorated. The patient's parents showed satisfaction towards the overall surgery, tongue's appearance, and tongue's motor function. Tongue's height decreased from 32.09±1.16 mm before the operation to 29.29±1.33 mm after the operation.

CONCLUSION

The partial glossectomy combined RFA exerts a safe, effective and viable technique to treat BWS-derived macroglossia.

Magnetic Resonance Image-Guided Focal Prostate Ablation

Prostate cancer is the most common cancer (other than skin cancer) in American men, with one in seven men being diagnosed with this disease during his lifetime. The estimated number of new prostate cancer cases in 2016 is 180,890. For the first time, imaging has become the center of the search for contained, intraglandular, small-volume, and unifocal disease, and an increasing number of academic institutions as well as private practices are implementing programs for prostate multiplanar magnetic resonance imaging (MRI) as parts of their routine offerings. This article reviews the role of MRI-guided focal prostate ablation, as well as opportunities for further growth in this minimally invasive therapy of prostate cancer.

Sleep Apnea Research in Animals. Past, Present, and Future

Obstructive sleep apnea (OSA) is a common disorder that describes recurrent collapse of the upper airway during sleep. Animal models have been pivotal to the understanding of OSA pathogenesis, consequences, and treatment. In this review, we highlight the history of OSA research in animals and include the discovery of animals with spontaneous OSA, the induction of OSA in animals, and the emulation of OSA using exposures to intermittent hypoxia and sleep fragmentation.

Osteoid osteoma treated with percutaneous radiofrequency ablation: MR imaging follow-up

PURPOSE

We evaluated follow-up magnetic resonance (MR) images for osteoid osteoma treated with percutaneous radiofrequency ablation (RFA).

MATERIALS AND METHODS

Sixteen patients with osteoid osteoma treated with RFA underwent follow-up MR imaging. The protocol included T1, T2 and contrast-enhanced (CE) T1-weighted images with fat saturation at each visit immediately for 17 months after the treatment. MR images were jointly reviewed by two radiologists, regarding the appearance of treated areas, presence of complications, and the best sequence for visualization of signal intensity (SI) changes. The therapeutic response was evaluated to be a clinical success with the relief of pain.

RESULTS

The treated areas had a target-like appearance on MR images: a central ablated zone (Z1) surrounded by a band (Z2), and a peripheral area (Z3). Z1 was a non-enhancing, hypointense core on T1, T2WI. Z2 was a well-enhancing, hyperintense rim on T2WI. Z3 was less hyperintense and less enhanced than Z2. All nidi were within Z1. This appearance became evident from 1 week to 1 and 2 months. Following up after 2 months, Z2 showed progressive inward enhancement from the periphery, resulting in almost complete enhancement of Z1 and Z2 with a diminishing size. Z3 gradually showed a decrease in signal change and enhancement. No complications were found. CE-T1WI was the best for visualizing SI changes. The clinical success was achieved in all patients except for one patient with a recurrence at 17 months following treatment that had a second ablation.

CONCLUSION

MR imaging demonstrated a characteristic appearance and subsequent changes of treated areas for osteoid osteoma following RFA.

Real time monitoring of radiofrequency ablation based on MR thermometry and thermal dose in the pig liver in vivo

To evaluate the feasibility and accuracy of MR thermometry based on the thermal dose (TD) concept for monitoring radiofrequency (RF) ablations, 13 RF ablations in pig livers were performed under continuous MR thermometry at 1.5 T with a filtered clinical RF device. Respiratory gated fast gradient echo images were acquired simultaneously to RF deposition for providing MR temperature maps with the proton resonant frequency technique. Residual motion, signal to noise ratio (SNR) and standard deviation (SD) of MR temperature images were quantitatively analyzed to detect and reject artifacted images in the time series. SD of temperature measurement remained under 2 degrees C. Macroscopic analysis of liver ablations showed a white zone (Wz) surrounded by a red zone (Rz). A detailed histological analysis confirmed the ongoing nature of the coagulation necrosis in both Wz and Rz. Average differences (+/-SD) between macroscopic size measurements of Wz and Rz and TD predictions of ablation zones were 4.1 (+/-1.93) mm and -0.71 (+/-2.47) mm, respectively. Correlation values between TD and Wz and TD and Rz were 0.97 and 0.99, respectively. MR thermometry monitoring based on TD is an accurate method to delineate the size of the ablation zone during the RF procedure and provides a clinical endpoint.

Cognitive effects of head-movements in stray fields generated by a 7 Tesla whole-body MRI magnet

The study investigates the impact of exposure to the stray magnetic field of a whole-body 7 T MRI scanner on neurobehavioral performance and cognition. Twenty seven volunteers completed four sessions, which exposed them to approximately 1600 mT (twice), 800 mT and negligible static field exposure. The order of exposure was assigned at random and was masked by placing volunteers in a tent to hide their position relative to the magnet bore. Volunteers completed a test battery assessing auditory working memory, eye-hand co-ordination, and visual perception. During three sessions the volunteers were instructed to complete a series of standardized head movements to generate additional time-varying fields ( approximately 300 and approximately 150 mT.s(-1) r.m.s.). In one session, volunteers were instructed to keep their heads as stable as possible. Performance on a visual tracking task was negatively influenced (P<.01) by 1.3% per 100 mT exposure. Furthermore, there was a trend for performance on two cognitive-motor tests to be decreased (P<.10). No effects were observed on working memory. Taken together with results of earlier studies, these results suggest that there are effects on visual perception and hand-eye co-ordination, but these are weak and variable between studies. The magnitude of these effects may depend on the magnitude of time-varying fields and not so much on the static field. While this study did not include exposure above 1.6 T, it suggests that use of strong magnetic fields is not a significant confounder in fMRI studies of cognitive function. Future work should further assess whether ultra-high field may impair performance of employees working in the vicinity of these magnets.

Characterization of acute and subacute radiofrequency ablation lesions with nonenhanced magnetic resonance imaging

BACKGROUND

Magnetic resonance imaging (MRI) has the potential to visualize radiofrequency (RF) ablations, which have become the preferred strategy for treatment of many arrhythmias. However, MRI patterns after RF ablation have not been well investigated.

OBJECTIVE

The purpose of this study was to define the characteristic appearance and the effect of time and energy on noncontrast-enhanced MRI of RF ablation.

METHODS

Using a power-controlled, cooled-tip ablation system, RF ablation lesions (5-50 W for 45 seconds) were created on the right ventricular epicardium in 10 mongrel dogs. T1- and T2-weighted MR images were obtained during 12-hour follow-up and compared with gross anatomy and histopathology.

RESULTS

Lesions were successfully visualized with T2- and T1-weighted images 30 minutes to 12 hours after RF ablation. T2 images were more consistent and displayed a characteristic elliptical, high-signal core (contrast-to-noise-ratio [CNR] = 18.9 +/- 8.4) with a surrounding 0.5-mm low-intensity rim that on histopathology corresponded to the central tissue necrosis and the transition zone, respectively. T1 images showed a less remarked increase in signal intensity (CNR = 9.6 +/- 7.4) without a surrounding rim. Lesion size and appearance were well defined and unchanged during the 12-hour follow-up (analysis of variance). CNR was independent of applied RF energy and allowed accurate assessment of RF ablation at all time points (r = 0.87 and r = 0.83 for T2 and T1 images, respectively). Transmural lesions, interlesional gaps, and intralesional pathology could be reliably predicted in >90%.

CONCLUSION

Noncontrast-enhanced MRI allows accurate assessment of RF ablation and its intralesional pathology during 12-hour follow-up. This finding confirms a possible role of MRI in guiding and evaluating RF application during electrophysiologic ablation procedures.

Radiofrequency Tongue Reduction Through a Cervical Approach: A Pilot Study

OBJECTIVE/HYPOTHESIS

The objective of this prospective cohort study was to determine the feasibility, safety, and efficacy of radiofrequency tongue base reduction through a cervical approach in patients with obstructive sleep apnea syndrome (OSAS).

METHODS

Patients with moderate to severe OSAS and predominant tongue base obstruction by physical examination were included at our institution from 1999 to 2003. A sonogram was obtained to identify the lingual arteries, and an electrode was inserted through the neck and into the tongue under fluoroscopic guidance. Adverse events were recorded as well as efficacy on snoring (visual analog scale), daytime sleepiness (Epworth score), and polysomnography.

RESULTS

The 10 patients received a mean of 14,288 +/- 3,251 J per session. No cases of tongue palsy or infection occurred. During the first 7 days, mean pain score (0-10 scale) was 1.3 +/- 1.5. Snoring volume (0-10 scale) decreased from 6.2 +/- 2.3 to 3.9 +/- 2.6 (P = .017) and sleepiness (0-24 scale) from 8.7 +/- 5.6 to 4.7 +/- 3.3 (P = .011). The respiratory disturbance index (events/hour) decreased from 52.0 +/- 19.6 to 33.6 +/- 24.4 (P = .016). Mean minimal oxygen saturation (%) increased from 64.2 +/- 13.0 to 75.8 +/- 10.3 (P = .003). Sleep architecture improved although not significantly.

CONCLUSION

Radiofrequency tongue base reduction through a cervical approach proved feasible and safe despite the large energy doses used. Fluoroscopic guidance enables to place the electrode at the desired site of treatment. Although OSAS improved in nine of 10 patients, greater efficacy might be achieved in patients with less severe OSAS at baseline. Studies are needed to correlate objective clinical efficacy with the dose per lesion site and the number of lesion sites per session.

Pulsed cavitational ultrasound therapy for controlled tissue homogenization

Methods were investigated to acoustically control the extent to which cavitation-mediated tissue homogenization is responsible for lesion formation in vitro. These results may guide potential therapeutic procedures that induce damage predominantly via mechanical disruption and, thereby, avoid limitations associated with thermal ablative modalities. Porcine myocardium was insonified at 750 kHz using pulse sequences consisting of high-amplitude pulses (22 MPa Pr) interleaved with variable-amplitude "sustaining" pulses (e.g., 6.9 MPa Pr), which were intended to provide sufficient acoustic input to maintain cavitation activity between primary pulses, but to increase the spatial peak temporal average intensity (I(SPTA)) only marginally. Using modest temporal-average intensities (e.g., I(SPTA) approximately 200 W/cm2), approximately 0.5 cm3 lesions were produced consisting of homogenate that could be irrigated away to reveal smooth cavities. The prevalence of homogenate in a given lesion was sensitive to both pulse-repetition frequency and sustaining pulse amplitude, suggesting the existence of optimum acoustic parameters for producing homogenized lesions largely via mechanical perturbation.

Radiofrequency Thermal Ablation: The Role of MR Imaging in Guiding and Monitoring Tumor Therapy

Performing RFA procedures under MR imaging involves two distinct processes: interactive guidance of the RF electrode into the targeted tumor and monitoring the effect of therapy. The justification for using MR imaging for electrode guidance is quite similar to its use to guide biopsy and aspiration procedures, where MR imaging offers advantages related to superior soft tissue contrast, multiplanar capabilities, and high vascular conspicuity that facilitate safe and accurate guidance in selected lesions. The major contribution of MR imaging to thermal ablation procedures is its ability to monitor tissue changes associated with the heating process instantaneously, an attribute that is not paralleled by any other currently available imaging modality. Such ability facilitates a controlled approach to ablation by helping to detect inadequately treated tumor foci for subsequent interactive repositioning of the RF electrode during therapy. As such, MR imaging guidance and monitoring enable treatment of the entire tumor on a single-visit basis while avoiding undue overtreatment and preserving often critically needed organ function. Although knowledge of interventional MR imaging concepts and familiarity with its technology and with the related safety issues are indispensable for interventional radiologists attempting thermal ablation procedures in the MR imaging environment, understanding the tissue basis of necrosis imaging is becoming an essential part of the knowledge base for the larger sector of general radiologists who are required to interpret the follow-up MR imaging scans of the increasing number of thermal ablation patients.

Static magnetic field effects on human subjects related to magnetic resonance imaging systems

GOAL

This paper reviews recent studies evaluating human subjects for physiologic or neuro-cognitive function adverse effects resulting from exposure to static magnetic fields of magnetic resonance imaging systems.

MATERIALS AND METHODS

The results of three studies are summarized. Two studies evaluated exposure to a maximum of 8 Tesla (T). The first series studied 25 normal human subjects' sequential vital signs (heart rate, blood pressure, blood oxygenation, core temperature, ECG, respiratory rate) measured at different magnetic field strengths to a maximum of 8 T. A second series of 25 subjects were studied at 0.05 and 8 T (out and in the bore of the magnet), performing 12 different standardized neuro-psychological tests and auditory-motor reaction times. The subjects' comments were recorded immediately following the study and after a three-month interval. The third study contained 17 subjects, placed near the bore of a 1.5 T magnet, and it used six different cognitive, cognitive-motor, or sensory tests.

RESULTS

There were no clinically significant changes in the subjects' physiologic measurements at 8 T. There was a slight increase in the systolic blood pressure with increasing magnetic field strength. There did not appear to be any adverse effect on the cognitive performance of the subjects at 8 T. A few subjects commented at the time of initial exposure on dizziness, metallic taste in the mouth, or discomfort related to the measurement instruments or the head coil. There were no adverse comments at 3 months. The 1.5 T study had two of the four neuro-behavioral domains exhibiting adverse effects (sensory and cognitive-motor).

CONCLUSIONS

These studies did not demonstrate any clinically relevant adverse effects on neuro-cognitive testing or vital sign changes. One short-term memory, one sensory, and one cognitive-motor test demonstrated adverse effects, but the significance is not clear.