MR thermometry imaging for low intensity focused ultrasound modulation of spinal nervous tissue.

OBJECTIVES: Previously in rodent and swine models, we have shown that external low intensity focused ultrasound (liFUS) can be used to modulate pain responses. To ensure no adverse heating events occur with liFUS modulation in a non-invasive manner, we perform initial work in swine to show that magnetic resonance thermometry imaging (MRTI) is capable of measuring <2.0 °C changes at the L5 DRG. Further, we show that our device can be constructed in an MR-compatible fashion to minimize artifact. METHODS: Three MRTI techniques (referenceless, corrected proton resonance frequency shift (PRFS), and PRFS) were applied to assess accuracy of detecting thermal changes at the L5 DRG in unheated euthanized swine. A region of interest (ROI) that includes the L5 DRG was delineated, within which MRTI temperature changes were spatially averaged (ground truth 0 °C). In separate experiments with phantoms, B0 field-inhomogeneity, RF transmit (B1+) and fast gradient echo (fSPGR) magnitude images were acquired to downselect liFUS device materials that produce the least MRI artifacts. RESULTS: Referenceless, corrected PRFS, and PRFS MRTI resulted in temperature measurements of 0.8 ± 1.1 °C, 1.1 ± 1.3 °C and 5.2 ± 5 °C, respectively. Both materials caused B0 perturbation but minimal B1+ and MRTI artifacts. The presence of imaging artifacts did not preclude thermal imaging of the region. SIGNIFICANCE: We provide preliminary data suggesting that referenceless MRTI can adequately detect small thermal changes at the DRG that may occur with neuromodulation, which is one of the first steps in creating a table of safe parameters for liFUS therapy in humans.

The effects of low intensity focused ultrasound on neuronal activity in pain processing regions in a rodent model of common peroneal nerve injury.

BACKGROUND: Non-invasive, external low intensity focused ultrasound (liFUS) offers promise for treating neuropathic pain when applied to the dorsal root ganglion (DRG). OBJECTIVE: We examine how external liFUS treatment applied to the L5 DRG affects neuronal changes in single-unit activity from the primary somatosensory cortex (SI) and anterior cingulate cortex (ACC) in a common peroneal nerve injury (CPNI) rodent model. METHODS: Male Sprague Dawley rats were divided into two cohorts: CPNI liFUS and CPNI sham liFUS. Baseline single-unit activity (SUA) recordings were taken 20 min prior to treatment and for 4 h post treatment in 20 min intervals, then analyzed for frequency and compared to baseline. Recordings from the SI and ACC were separated into pyramidal and interneurons based on waveform and principal component analysis. RESULTS: Following CPNI surgery, all rats (n = 30) displayed a significant increase in mechanical sensitivity. In CPNI liFUS rats, there was a significant increase in pyramidal neuron spike frequency in the SI region compared to the CPNI sham liFUS animals beginning at 120 min following liFUS treatment (p < 0.05). In the ACC, liFUS significantly attenuated interneuron firing beginning at 80 min after liFUS treatment (p < 0.05). CONCLUSION: We demonstrate that liFUS changed neuronal spiking in the SI and ACC regions 80 and 120 min after treatment, respectively, which may in part correlate with improved sensory thresholds. This may represent a mechanism of action how liFUS attenuates neuropathic pain. Understanding the impact of liFUS on pain circuits will help advance the use of liFUS as a non-invasive neuromodulation option.

Low Intensity Focused Ultrasound Increases Duration of Anti-Nociceptive Responses in Female Common Peroneal Nerve Injury Rats.

OBJECTIVE: Chronic pain affects 7%-10% of Americans, occurs more frequently and severely in females, and available treatments have been shown to have less efficacy in female patients. Preclinical models addressing sex-specific treatment differences in the treatment of chronic pain have been limited. Here we examine the sex-specific effects of low intensity focused ultrasound (liFUS) in a modified sciatic nerve injury (SNI) model. MATERIALS AND METHODS: A modified SNI performed by ligating the common peroneal nerve (CPN) was used to measure sensory, behavioral pain responses, and nerve conduction studies in female and male rats, following liFUS of the L5 dorsal root ganglion. RESULTS: Using the same dose of liFUS in females and males of the same weight, CPN latency immediately after treatment was increased for 50 min in females compared to 25 min in males (p < 0.001). Improvements in mechanical pain thresholds after liFUS lasted significantly longer in females (seven days; p < 0.05) compared to males (three days; p < 0.05). In females, there was a significant improvement in depression-like behavior as a result of liFUS (N = 5; p < 0.01); however, because males never developed depression-like behavior there was no change after liFUS treatment. CONCLUSIONS: Neuromodulation with liFUS has a greater effect in female rats on CPN latency, mechanical allodynia duration, and depression-like behavior. In order to customize neuromodulatory techniques for different patient phenotypes, it is essential to understand how they may alter sex-specific pathophysiologies.

Effects of external low intensity focused ultrasound on inflammatory markers in neuropathic pain.

BACKGROUND: Changes in inflammatory cytokine levels contribute to the induction and maintenance of neuropathic pain. We have shown that external low intensity focused ultrasound (liFUS) reduces allodynia in a common peroneal nerve injury (CPNI). Here, we investigate an underlying mechanism of action for this treatment and measure the effect of liFUS on inflammatory markers. METHODS: Male rats were divided into four groups: CPNI/liFUS, CPNI/shamliFUS, shamCPNI/liFUS, and shamCPNI/shamliFUS. Mechanical nociceptive thresholds were measured using Von Frey filaments (VFF) to confirm the absence/presence of allodynia at baseline, after CPNI, and after liFUS. Commercial microarray and ELISA assays were used to assess cytokine expression in the treated L5 dorsal root ganglion (DRG) and dorsal horn (DH) tissue 24 and 72 h after liFUS. RESULTS: VFF thresholds were significantly reduced following CPNI in both groups that received the injury (p < 0.001). After liFUS, only the CPNI/liFUS cohort showed a significant increase in mechanical thresholds (p < 0.001). CPNI significantly increased TNFa, IL6, CNTF, IL1b (p < 0.05 for all) levels in the DRG and DH, compared to baseline, consistent with previous work in sciatic nerve injury. LiFUS in CPNI rats resulted in a decrease in these cytokines in DRG 72 h post-therapy (TNFa, IL6, CNTF and IL1b, p < 0.001). In the DH, IL1b, CNTF, and TNFa (p < 0.05 for all) decreased 72 h after liFUS. CONCLUSION: We have demonstrated that liFUS modifies inflammatory cytokines in both DRG and DH in CPNI rats. These data provide evidence that liFUS, reverses the allodynic phenotype, in part, by altering inflammatory cytokine pathways.

Pilot study on the effects of low intensity focused ultrasound in a swine model of neuropathic pain.

OBJECTIVE: The authors' laboratory has previously demonstrated beneficial effects of noninvasive low intensity focused ultrasound (liFUS), targeted at the dorsal root ganglion (DRG), for reducing allodynia in rodent neuropathic pain models. However, in rats the DRG is 5 mm below the skin when approached laterally, while in humans the DRG is typically 5-8 cm deep. Here, using a modified liFUS probe, the authors demonstrated the feasibility of using external liFUS for modulation of antinociceptive responses in neuropathic swine. METHODS: Two cohorts of swine underwent a common peroneal nerve injury (CPNI) to induce neuropathic pain. In the first cohort, pigs (14 kg) were iteratively tested to determine treatment parameters. liFUS penetration to the L5 DRG was verified by using a thermocouple to monitor tissue temperature changes and by measuring nerve conduction velocity (NCV) at the corresponding common peroneal nerve (CPN). Pain behaviors were monitored before and after treatment. DRG was evaluated for tissue damage postmortem. Based on data from the first cohort, a treatment algorithm was developed, parameter predictions were verified, and neuropathic pain was significantly modified in a second cohort of larger swine (20 kg). RESULTS: The authors performed a dose-response curve analysis in 14-kg CPNI swine. Specifically, after confirming that the liFUS probe could reach 5 cm in ex vivo tissue experiments, the authors tested liFUS in 14-kg CPNI swine. The mean ± SEM DRG depth was 3.79 ± 0.09 cm in this initial cohort. The parameters were determined and then extrapolated to larger animals (20 kg), and predictions were verified. Tissue temperature elevations at the treatment site did not exceed 2°C, and the expected increases in the CPN NCV were observed. liFUS treatment eliminated pain guarding in all animals for the duration of follow-up (up to 1 month) and improved allodynia for 5 days postprocedure. No evidence of histological damage was seen using Fluoro-Jade and H&E staining. CONCLUSIONS: The results demonstrate that a 5-cm depth can be reached with external liFUS and alters pain behavior and allodynia in a large-animal model of neuropathic pain.

Effects of external low intensity focused ultrasound on electrophysiological changes in vivo in a rodent model of common peroneal nerve injury.

Non-invasive treatment methods for neuropathic pain are lacking. We assess how modulatory low intensity focused ultrasound (liFUS) at the L5 dorsal root ganglion (DRG) affects behavioral responses and sensory nerve action potentials (SNAPs) in a common peroneal nerve injury (CPNI) model. Rats were assessed for mechanical and thermal responses using Von Frey filaments (VFF) and the hot plate test (HPT) following CPNI surgery. Testing was repeated 24 h after liFUS treatment. Significant increases in mechanical and thermal sensory thresholds were seen post-liFUS treatment, indicating a reduction in sensitivity to pain (p < 0.0001, p = 0.02, respectively). Animals who received CPNI surgery had significant increases in SNAP latencies compared to sham CPNI surgery animals (p = 0.0003) before liFUS treatment. LiFUS induced significant reductions in SNAP latency in both CPNI liFUS and sham CPNI liFUS cohorts, for up to 35 min post treatment. No changes were seen in SNAP amplitude and there was no evidence of neuronal degeneration 24 h after liFUS treatment, showing that liFUS did not damage the tissue being modulated. This is the first in vivo study of the impact of liFUS on peripheral nerve electrophysiology in a model of chronic pain. This study demonstrates the effects of liFUS on peripheral nerve electrophysiology in vivo. We found that external liFUS treatment results in transient decreased latency in common peroneal nerve (CPN) sensory nerve action potentials (SNAPs) with no change in signal amplitude.

Low Intensity Focused Ultrasound Modulation of Vincristine Induced Neuropathy.

Previously, we showed internal low intensity focused ultrasound (liFUS) improves nociceptive thresholds in rats with vincristine-induced neuropathy (VIN) for 48-h post-treatment. Here, we perform more rigorous behavioral testing with the internal device and introduce external liFUS treatment. Behavioral testing confirmed VIN (Von Frey fibers, VFF; hot plate, HPT; locomotion, OFT). This was followed by internal or external liFUS treatment (2.5 W or 8 W, for 3 min, respectively) to the left L5 dorsal root ganglia (DRG). A thermocouple placed at the DRG documented temperature changes during treatment, to confirm the modulatory nature of our treatment. Behavioral testing was performed pre-liFUS, and for five consecutive days post-liFUS. Groups included: (1) VIN/liFUS, (2) saline/liFUS, (3) VIN/sham liFUS, and (4) saline/sham liFUS. Significant improvements in mechanical (VFF) and thermal (HPT) nociceptive thresholds were seen in the VIN/liFUS group following both internal and external treatment. Hematoxylin and Eosin, and Fluorojade staining showed no histological damage to the DRG. Internal liFUS treatment produced a mean temperature rise of 3.21 ±â€¯0.30 °C, whereas external liFUS resulted in a mean temperature rise of 1.78 °C ±â€¯0.21 °C. We demonstrate that, in a VIN rat model, external liFUS treatment of the L5 DRG significantly reduces nociceptive sensitivity thresholds without causing tissue damage.

The use of focused ultrasound for the treatment of cutaneous allodynia associated with chronic migraine.

Chronic migraines (CM) are the third most common disease and are refractory to medical treatment in 15% of patients. Currently, temporary relief is achieved with steroid blocks or pulsed radiofrequency ablation, which have short-term benefits. Our project aims to develop a non-invasive treatment for medically refractory chronic migraine, which does not require a permanent implant. This project investigates the safety and effectiveness of pulsed focused ultrasound (FUS) in a validated rodent headache model of cutaneous allodynia associated with chronic migraine (CM) as compared to sumatriptan and ablative lesioning. We demonstrate a significant reduction in mechanical thresholds as measured through Von Frey filaments in CM in the forepaw and periorbital region (p < 0.001). Sumatriptan and pulsed FUS both significantly improve thresholds at day 3 after treatment in the periorbital region. Ablative lesioning has no effect. This study provides initial evidence that FUS may provide an important therapeutic option for patients suffering from CM.

External focused ultrasound treatment for neuropathic pain induced by common peroneal nerve injury.

Neuropathic pain caused by nerve injury or compressive lesions is a debilitating condition lacking effective, long-term treatments. Our objective was to assess the effects of external focused ultrasound on sensory thresholds utilizing a common peroneal injury rat model. CPNI was induced by ligating the CPN of the left hind paw. Neuropathic phenotype was confirmed using the Von Frey Fibers (VFF) with a 50% mechanical detection threshold below 4.0. The Place Escape Avoidance Paradigm (PEAP) was employed as a behavioral correlate. External FUS treatment was applied to the left L4,5 DRG at 8 W for 3-min. There were two treatment groups; one received a single FUS treatment, while the other received two. Control groups consisted of one sham CPNI group that received FUS treatment and a CPNI group that received sham FUS treatment. Behavioral tests were conducted pre-CPNI surgery, 1-week post-surgery, and for 1-week post-FUS treatment(s). CPNI surgery resulted in lower VFF mechanical thresholds in the left hind paw compared to baseline (p < 0.0001) and increased proportion of time spent on bright side compared to baseline values on PEAP (p = 0.0473), indicating neuropathic state. FUS treatment increased VFF thresholds after 24-hours (p < 0.0001), 48-h (p = 0.0079), and 72-h (p = 0.0164). VFF returned to baseline values from day 4-7. Following a second FUS treatment on day 8, increased mechanical thresholds were similarly observed after 24-h (p = 0.0021), 48-h (p < 0.0001), and 72-h (p = 0.0256). Control group analysis showed (1) CPNI rats experienced no change in mechanical thresholds following sham FUS treatment and (2) Sham CPNI rats receiving FUS did not experience significantly different mechanical thresholds compared to baseline and post-CPNI values. Post-FUS histological analysis demonstrated healthy ganglion cells without chromatolysis. Our results demonstrate changes in VFF and PEAP in rats who underwent CPNI. Single and multiple doses of external FUS increase mechanical thresholds without inducing histological damage. Based on our results, we have demonstrated the potential of FUS to serve as a non-pharmacological and non-ablative neuromodulatory approach for the treatment of allodynia and neuropathic pain.

High-Intensity Ultrasound Treatment for Vincristine-Induced Neuropathic Pain.

BACKGROUND: Vincristine is a commonly used chemotherapeutic agent that results in debilitating untreatable peripheral neuropathy. OBJECTIVE: To determine the effects of pulsed high-intensity focused ultrasound (HIFU) on sensory thresholds in a validated vincristine-induced neuropathy (VIN) rodent model. METHODS: VIN was induced and mechanical allodynia was confirmed by nociceptive testing. von Frey fibers and Randall-Sellito test were used as measures of innocuous and noxious mechanical thresholds, respectively, and the hot plate test for thermal thresholds. Tests were performed before VIN, after 2 wk of vincristine, at 24, 48, 72, and 120 h after HIFU applied to the left L5 dorsal root ganglia at 3 Watts for 3 min. Comparisons were made between a VIN cohort who underwent HIFU, a VIN cohort who underwent sham HIFU, and naïve rodents who underwent HIFU. RESULTS: VIN HIFU rats had significantly increased mechanical thresholds at 24 h (P < .001), 48 h (P = .008), 72 h (P = .003), and 120 h (P = .03) after treatment, when compared to pre-HIFU thresholds. Furthermore, at 24 and 48 h following treatment, VIN HIFU rats had significantly higher innocuous and noxious mechanical thresholds and thermal thresholds than VIN sham HIFU rats (P < .001). Thresholds were not altered in naïve rodents who underwent HIFU. Histological data of L5 dorsal root ganglia of VIN HIFU rats suggest that transient cellular edema resolves by 48 h. CONCLUSION: Our data suggest that HIFU increases mechanical and thermal thresholds in VIN rodents. Whether HIFU can preclude the development of reduced thresholds in the VIN model warrants further study.

C-arm pose estimation in prostate brachytherapy by registration to ultrasound.

In prostate brachytherapy, transrectal ultrasound (TRUS) is used to visualize the anatomy, while implanted seeds can be seen in C-arm fluoroscopy. Intra-operative dosimetry optimization requires reconstruction of the implanted seeds from multiple C-arm fluoroscopy images, which in turn requires estimation of the C-arm poses. We estimate the pose of the C-arm by two-stage registration between the 2D fluoroscopy images to a 3D TRUS volume. As single-view 2D/3D registration tends to yield depth error, we first estimate the depth from multiple 2D fluoro images and input this to a single-view 2D/3D registration. A commercial phantom was implanted with seeds and imaged with TRUS and CT. Ground-truth registration was established between the two by radiographic fiducials. Synthetic ground-truth fluoro images were created from the CT volume and registered to the 3D TRUS. The average rotation and translation errors were 1.0 degrees (STD = 2.3 degrees) and 0.7 mm (STD = 1.9 mm), respectively. In data from a human patient, the average rotation and lateral translation errors were 0.6 degrees (STD = 3.0 degrees) and 1.5 mm (STD = 2.8 mm), respectively, relative to the ground-truth established by a radiographic fiducial. Fully automated image-based C-arm pose estimation was demonstrated in prostate brachytherapy. Accuracy and robustness was excellent on phantom. Early result in human patient data appears clinically adequate.

FTRAC--a robust fluoroscope tracking fiducial.

C-arm fluoroscopy is ubiquitous in contemporary surgery, but it lacks the ability to accurately reconstruct three-dimensional (3D) information. A major obstacle in fluoroscopic reconstruction is discerning the pose of the x-ray image, in 3D space. Optical/magnetic trackers tend to be prohibitively expensive, intrusive and cumbersome in many applications. We present single-image-based fluoroscope tracking (FTRAC) with the use of an external radiographic fiducial consisting of a mathematically optimized set of ellipses, lines, and points. This is an improvement over contemporary fiducials, which use only points. The fiducial encodes six degrees of freedom in a single image by creating a unique view from any direction. A nonlinear optimizer can rapidly compute the pose of the fiducial using this image. The current embodiment has salient attributes: small dimensions (3 x 3 x 5 cm); need not be close to the anatomy of interest; and accurately segmentable. We tested the fiducial and the pose recovery method on synthetic data and also experimentally on a precisely machined mechanical phantom. Pose recovery in phantom experiments had an accuracy of 0.56 mm in translation and 0.33 degrees in orientation. Object reconstruction had a mean error of 0.53 mm with 0.16 mm STD. The method offers accuracies similar to commercial tracking systems, and appears to be sufficiently robust for intraoperative quantitative C-arm fluoroscopy. Simulation experiments indicate that the size can be further reduced to 1 x 1 X 2 cm, with only a marginal drop in accuracy.