Transcranial ultrasound neuromodulation of the thalamic visual pathway in a large animal model and the dose-response relationship with MR-ARFI.

Neuromodulation of deep brain structures via transcranial ultrasound stimulation (TUS) is a promising, but still elusive approach to non-invasive treatment of brain disorders. The purpose of this study was to confirm that MR-guided TUS of the lateral geniculate nucleus (LGN) can modulate visual evoked potentials (VEPs) in the intact large animal; and to study the impact on cortical brain oscillations. The LGN on one side was identified with T2-weighted MRI in sheep (all male, n = 9). MR acoustic radiation force imaging (MR-ARFI) was used to confirm localization of the targeted area in the brain. Electroencephalographic (EEG) signals were recorded, and the visual evoked potential (VEP) peak-to-peak amplitude (N70 and P100) was calculated for each trial. Time-frequency spectral analysis was performed to elucidate the effect of TUS on cortical brain dynamics. The VEP peak-to-peak amplitude was reversibly suppressed relative to baseline during TUS. Dynamic spectral analysis demonstrated a change in cortical oscillations when TUS is paired with visual sensory input. Sonication-associated microscopic displacements, as measured by MR-ARFI, correlated with the TUS-mediated suppression of visual evoked activity. TUS non-invasively delivered to LGN can neuromodulate visual activity and oscillatory dynamics in large mammalian brains.

Histologic safety of transcranial focused ultrasound neuromodulation and magnetic resonance acoustic radiation force imaging in rhesus macaques and sheep.

BACKGROUND: Neuromodulation by transcranial focused ultrasound (FUS) offers the potential to non-invasively treat specific brain regions, with treatment location verified by magnetic resonance acoustic radiation force imaging (MR-ARFI). OBJECTIVE: To investigate the safety of these methods prior to widespread clinical use, we report histologic findings in two large animal models following FUS neuromodulation and MR-ARFI. METHODS: Two rhesus macaques and thirteen Dorset sheep were studied. FUS neuromodulation was targeted to the primary visual cortex in rhesus macaques and to subcortical locations, verified by MR-ARFI, in eleven sheep. Both rhesus macaques and five sheep received a single FUS session, whereas six sheep received repeated sessions three to six days apart. The remaining two control sheep did not receive ultrasound but otherwise underwent the same anesthetic and MRI procedures as the eleven experimental sheep. Hematoxylin and eosin-stained sections of brain tissue (harvested zero to eleven days following FUS) were evaluated for tissue damage at FUS and control locations as well as tissue within the path of the FUS beam. TUNEL staining was used to evaluate for the presence of apoptosis in sheep receiving high dose FUS. RESULTS: No FUS-related pre-mortem histologic findings were observed in the rhesus macaques or in any of the examined sheep. Extravascular red blood cells (RBCs) were present within the meninges of all sheep, regardless of treatment group. Similarly, small aggregates of perivascular RBCs were rarely noted in non-target regions of neural parenchyma of FUS-treated (8/11) and untreated (2/2) sheep. However, no concurrent histologic abnormalities were observed, consistent with RBC extravasation occurring as post-mortem artifact following brain extraction. Sheep within the high dose FUS group were TUNEL-negative at the targeted site of FUS. CONCLUSIONS: The absence of FUS-related histologic findings suggests that the neuromodulation and MR-ARFI protocols evaluated do not cause tissue damage.

Multimodality Hyperpolarized C-13 MRS/PET/Multiparametric MR Imaging for Detection and Image-Guided Biopsy of Prostate Cancer: First Experience in a Canine Prostate Cancer Model.

PURPOSE: To assess whether simultaneous hyperpolarized C-13 magnetic resonance spectroscopy (MRS)/positron emission tomography (PET)/multiparametric magnetic resonance (mpMR) imaging is feasible in an orthotopic canine prostate cancer (PCa) model using a clinical PET/MR system and whether the combined imaging datasets can be fused with transrectal ultrasound (TRUS) in real time for multimodal image fusion-guided targeted biopsy of PCa. PROCEDURES: Institutional Animal Care and Use Committee approval was obtained for this study. Canine prostate adenocarcinoma (Ace-1) cells were orthotopically injected into the prostate of four dogs. Once tumor engraftment was confirmed by TRUS, simultaneous hyperpolarized C-13 MRS of [1-13C]pyruvate, PET (2-deoxy-2-[18F]fluoro-D-glucose ([18F]FDG), [68Ga]NODAGA-SCH1), and mpMR (T2W, DWI) imaging was performed using a clinical PET/MR system. Multimodality imaging data sets were then fused with TRUS and image-guided targeted biopsy was performed. Imaging results were then correlated with histological findings. RESULTS: Successful tumor engraftment was histologically confirmed in three of the four dogs (dogs 2, 3, and 4) and simultaneous C-13 MRS/PET/mpMR was feasible in all three. In dog 2, C-13 MRS showed increased lactate signal in the tumor (lactate/totalC = 0.47) whereas mpMR did not show any signal changes. In dog 3, [18F]FDG-PET (SUVmean = 1.90) and C-13 MRS (lactate/totalC = 0.59) showed elevated metabolic activity in the tumor. In dog 4, [18F]FDG (SUVmean = 2.43), [68Ga]NODAGA-SCH1 (SUVmean = 0.75), and C-13 MRS (Lac/totalC = 0.53) showed elevated uptake in tumor compared to control tissue and multimodal image fusion-guided biopsy of the tumor was successfully performed. CONCLUSION: Simultaneous C-13 MRS/PET/mpMR imaging and multimodal image fusion-guided biopsy is feasible in a canine PCa model.

An intravascular magnetic wire for the high-throughput retrieval of circulating tumour cells in vivo.

The detection and analysis of rare blood biomarkers is necessary for early diagnosis of cancer and to facilitate the development of tailored therapies. However, current methods for the isolation of circulating tumour cells (CTCs) or nucleic acids present in a standard clinical sample of only 5-10 ml of blood provide inadequate yields for early cancer detection and comprehensive molecular profiling. Here, we report the development of a flexible magnetic wire that can retrieve rare biomarkers from the subject's blood in vivo at a much higher yield. The wire is inserted and removed through a standard intravenous catheter and captures biomarkers that have been previously labelled with injected magnetic particles. In a proof-of-concept experiment in a live porcine model, we demonstrate the in vivo labelling and single-pass capture of viable model CTCs in less than 10 s. The wire achieves capture efficiencies that correspond to enrichments of 10-80 times the amount of CTCs in a 5-ml blood draw, and 500-5,000 times the enrichments achieved using the commercially available Gilupi CellCollector.

Reduction of Muscle Contractions during Irreversible Electroporation Therapy Using High-Frequency Bursts of Alternating Polarity Pulses: A Laboratory Investigation in an Ex Vivo Swine Model.

PURPOSE: To compare the intensity of muscle contractions in irreversible electroporation (IRE) treatments when traditional IRE and high-frequency IRE (H-FIRE) waveforms are used in combination with a single applicator and distal grounding pad (A+GP) configuration. MATERIALS AND METHODS: An ex vivo in situ porcine model was used to compare muscle contractions induced by traditional monopolar IRE waveforms vs high-frequency bipolar IRE waveforms. Pulses with voltages between 200 and 5,000 V were investigated, and muscle contractions were recorded by using accelerometers placed on or near the applicators. RESULTS: H-FIRE waveforms reduced the intensity of muscle contractions in comparison with traditional monopolar IRE pulses. A high-energy burst of 2-µs alternating-polarity pulses energized for 200 µs at 4,500 V produced less intense muscle contractions than traditional IRE pulses, which were 25-100 µs in duration at 3,000 V. CONCLUSIONS: H-FIRE appears to be an effective technique to mitigate the muscle contractions associated with traditional IRE pulses. This may enable the use of voltages greater than 3,000 V necessary for the creation of large ablations in vivo.

Anatomical Road Mapping Using CT and MR Enterography for Ultrasound Molecular Imaging of Small Bowel Inflammation in Swine.

OBJECTIVES: To evaluate the feasibility and time saving of fusing CT and MR enterography with ultrasound for ultrasound molecular imaging (USMI) of inflammation in an acute small bowel inflammation of swine. METHODS: Nine swine with ileitis were scanned with either CT (n = 3) or MR (n = 6) enterography. Imaging times to load CT/MR images onto a clinical ultrasound machine, fuse them to ultrasound with an anatomical landmark-based approach, and identify ileitis were compared to the imaging times without anatomical road mapping. Inflammation was then assessed by USMI using dual selectin-targeted (MBSelectin) and control (MBControl) contrast agents in diseased and healthy control bowel segments, followed by ex vivo histology. RESULTS: Cross-sectional image fusion with ultrasound was feasible with an alignment error of 13.9 ± 9.7 mm. Anatomical road mapping significantly reduced (P < 0.001) scanning times by 40%. Localising ileitis was achieved within 1.0 min. Subsequently performed USMI demonstrated significantly (P < 0.001) higher imaging signal using MBSelectin compared to MBControl and histology confirmed a significantly higher inflammation score (P = 0.006) and P- and E-selectin expression (P ≤ 0.02) in inflamed vs. healthy bowel. CONCLUSIONS: Fusion of CT and MR enterography data sets with ultrasound in real time is feasible and allows rapid anatomical localisation of ileitis for subsequent quantification of inflammation using USMI. KEY POINTS: • Real-time fusion of CT/MRI with ultrasound to localise ileitis is feasible. • Anatomical road mapping using CT/MRI significantly decreases the scanning time for USMI. • USMI allows quantification of inflammation in swine, verified with ex vivo histology.

Dynamic Measurement of Arterial Liver Perfusion With an Interventional C-Arm System.

PURPOSE: Objective intraprocedural measurement of hepatic blood flow could provide a quantitative treatment end point for locoregional liver procedures. This study aims to validate the accuracy and reproducibility of cone-beam computed tomography perfusion (CBCTp) measurements of arterial liver perfusion (ALP) against clinically available computed tomography perfusion (CTp) measurements in a swine embolization model. METHODS: Triplicate CBCTp measurements using a selective arterial contrast injection were performed before and after complete embolization of the left lobe of the liver in 5 swine. Two CBCTp protocols were evaluated that differed in sweep duration (3.3 vs 4.5 seconds) and the number of acquired projection images (166 vs 248). The mean ALP was measured within identical volumes of interest selected in the embolized and nonembolized regions of the perfusion map generated from each scan. Postembolization CBCTp values were also compared with CTp measurements. RESULTS: The 2 CBCTp protocols demonstrated high concordance correlation (0.90, P < 0.001). Both CBCTp protocols showed higher reproducibility than CTp in the nontarget lobe, with an intraclass correlation of 0.90 or greater for CBCTp and 0.83 for CTp (P < 0.001 for all correlations). The ALP in the embolized lobe was nearly zero and hence excluded for reproducibility. High concordance correlation was observed between the CTp and each CBCTp protocol, with the shorter CBCTp protocol reaching a concordance correlation of 0.75 and the longer achieving 0.87 (P < 0.001 for both correlations). CONCLUSIONS: Dynamic blood flow measurement using an angiographic C-arm system is feasible and produces quantitative results comparable to CTp.

Histologic findings of disc, end plate and neural elements after coblation of nucleus pulposus: an experimental nucleoplasty study.

BACKGROUND CONTEXT: Partial removal of the nucleus has been shown to decompress herniated discs, relieving pressure on nerve roots and, in some cases, offering relief from disc pain. The nucleoplasty technique builds on earlier surgical approaches that helped validate the strategy of intranuclear tissue removal. Nucleoplasty, a new minimally invasive procedure using patented coblation technology, combines coagulation and ablation for partial removal of the nucleus pulposus to decompress the disc. PURPOSE: To determine if histologic changes of the intervertebral discs and surrounding tissues occur after nucleoplasty. STUDY DESIGN: A light microscopic study of intervertebral disc and adjacent neural tissues after disc decompression by nucleoplasty in pig cadavers. METHODS: Light microscopy was used to examine disc and neural tissues in two pig cadaveric specimens (T12 to sacrum). Nucleoplasty was performed by 1) advancing a radiofrequency wand to a predetermined depth in the disc (ablation), and 2) withdrawing the wand to the starting point (coagulation). Discs and adjacent tissues were removed from treated and nontreated segments, and examined under light microscopy. RESULTS: Histologic examination revealed no evidence of direct mechanical or thermal damage to the surrounding tissues. There was clear evidence of coblation channels with clean coagulation borders of the nucleus pulposus. Normal histologic findings of the annulus and end plate, with normal neural elements of the spinal cord and nerve roots at the level of the procedure, were observed. CONCLUSIONS: The histologic findings of this study suggest that the nucleoplasty achieves volumetric removal of target disc tissue without overt thermal or structural damage to the adjacent tissues. Further studies in live animals will be needed to assess the effects of nucleoplasty on the annulus, end plate and neural tissues under physiologic conditions, including assessment of cell viability.

A porcine model for endolaparoscopic abdominal aortic repair and endoscopic training.

OBJECTIVES: The goals of this laboratory model were to evaluate the performance of the surgical team and endolaparoscopic techniques in the porcine model of infrarenal abdominal aortic repair. METHODS: Twenty-four pigs underwent full endolaparoscopic aorto-aortic graft implantation with voice-activated computerized robotics. The first group of 10 pigs (acute) was sacrificed while under anesthesia at 0.5 hours (5 animals) and 2 hours (5 animals). The second group of 14 pigs (survival) were recovered from anesthesia and maintained for 7 hours (5 pigs) and 7 days (9 pigs) prior to sacrifice. Survival animals were observed for evidence of hind limb dysfunction. All grafts were visually inspected at autopsy. RESULTS: All animals survived the operation. All grafts were successfully implanted, and all were patent with intact anastomoses at autopsy. Mean aortic clamp time for each group was as follows: acute, 92.9 +/- 28.04 minutes; survival, 59.6 +/- 13.8 minutes; P=0.0008. Total operative time for each group was as follows: acute, 179 +/- 39.6 minutes; survival, 164.6 +/- 48 minutes; P=0.44 ns. Estimated blood loss for each group was as follows: acute, 214 -/+ 437.8 mL; survival 169.2 +/- 271 mL; P=0.76 ns. from respiratory arrest; 1 animal suffered motor sensory dysfunction of the hind limbs (spinal cord ischemia); significant bleeding occurred in 6 of 24 pigs; 8 of the 9 seven-day survivors required minimal pain medication and had normal hind limb function. CONCLUSIONS: The reduction in aortic clamp time, total operative time, and blood loss as the study progressed indicate the feasibility of this surgical protocol and the maturation of the learning process, which is paramount in prevention of 2 main sources of morbidity: bleeding and spinal cord ischemia. The reduction in aortic clamp time between the acute and survival groups was dramatic and statistically significant. An intensive formal training program combining dry and live surgical laboratories is deemed essential for the development of endoscopic skill sets necessary for this challenging procedure.

Endoscopic selective neck dissection in a porcine model.

OBJECTIVE: To investigate the feasibility of accomplishing a selective neck dissection (SND) endoscopically. STUDY DESIGN: Prospective, nonrandomized experimental investigation in a porcine model. METHODS: Unilateral endoscopic SNDs were performed in Yorkshire pigs. A spacious operative pocket was developed using a combination of hernia balloon expansion followed by low-pressure (4 mm Hg) carbon dioxide insufflation. The sternomastoid muscle, thymus, submandibular gland, lymph nodes, and fibrofatty tissue were removed in a procedure approximating a human SND. Data (operative time, blood loss, arterial blood gas values, weight of the specimen, and complications) were prospectively recorded. The specimens were analyzed by a pathologist, and the number and size of lymph nodes were recorded. RESULTS: Fourteen endoscopic SNDs were successfully performed. No conversions to open surgery were necessary. The median operative time was 131 minutes (range, 95-235 minutes). The median estimated blood loss was 4 mL (range, 0-150 mL). The mean +/- SD specimen weight was 42.9 +/- 8.3 g; the mean number +/- SD of nodes retrieved from the neck specimen was 4.8 +/- 2.2, and the mean +/- SD maximal nodal dimension was 2.4 +/- 0.5 cm. The arterial PCO2 increased by an average of only 3.9 mm Hg from the beginning to the end of the surgery; correspondingly, the pH fell by only 0.02. There were no major complications, and no animals had to be euthanized prior to the completion of the procedure. CONCLUSIONS: Endoscopic neck dissection in a porcine model can be accomplished with a combination of strategies to overcome the dilemma of creating and maintaining an operative pocket. The merger of SND with endoscopic technology offers the promise of truly minimally invasive surgery for the node-negative neck.

Endoscopic resection of the submandibular gland in a porcine model.

OBJECTIVE: To examine the feasibility of endoscopic resection of the submandibular gland in a porcine model. STUDY DESIGN: Experimental, nonrandomized prospective study. METHODS: Twelve endoscopic submandibular gland resections were performed on seven Yorkshire adult pigs using a combination of balloon dissection and low-pressure CO2 insufflation. The operative time, blood loss, blood pressure, oxygen saturation, temperature, arterial blood gas values, and weight of the glands were measured. RESULTS: All 12 submandibular gland resections were successfully performed endoscopically, and no conversions to open resection were necessary. The procedures lasted 42 to 140 minutes (median duration, 59 min). The median estimated blood loss was 15 mL. The submandibular glands weighed 13.3 +/- 1.5 g. The arterial blood pH varied from a decrease of 0.08 to an increase of 0.09 units from the beginning to the end of the operation. Similarly, the arterial CO2 pressure at the end of the case varied from a decrease of 15.8 to an increase of 16.2 mm Hg from the starting value. The presence of normal glandular architecture and lack of trauma or thermal injury were confirmed histologically. There were no cases of pneumothorax or air embolism, and no animals had to be killed. In one animal, a modest amount of subcutaneous emphysema could be appreciated, which was confined to the area over the operative pocket. CONCLUSION: Endoscopic resection of the submandibular gland is possible by combining balloon dissection with low-pressure CO2 insufflation, thereby avoiding complications of high-pressure insufflation such as pneumothorax and air embolism.

Mucus secretion from single submucosal glands of pig. Stimulation by carbachol and vasoactive intestinal peptide.

Secretion rates of >700 individual glands in isolated tracheal mucosa from 56 adult pigs were monitored optically. "Basal" secretion of 0.7 +/- 0.1 nl x min(-1) gland(-1) was observed 1-9 h post-harvest but was near zero on day 2. Secretion to carbachol (10 microm) peaked at 2-3 min and then declined to a sustained phase. Peak secretion was 12.4 +/- 1.1 nl x min(-1) gland(-1); sustained secretion was approximately one-third of peak secretion. Thapsigargin (1 microm) increased secretion from 0.1 +/- 0.05 to 0.7 +/- 0.2 nl x min(-1) gland(-1); thapsigargin did not cause contraction of the trachealis muscles. Isoproterenol and phenylephrine (10 microm each) were ineffective, but vasoactive intestinal peptide (1 microm) and forskolin (10 microm) each produced sustained secretion of 1.0 +/- 0.5 and 1.7 +/- 0.2 nl x min(-1) gland(-1), respectively. The density of actively secreting glands was 1.3/mm(2). Secretion to either carbachol or forskolin was inhibited (approximately 50%) by either bumetanide or HCO(3)(-) removal and inhibited approximately 90% by the combined treatments. Mucus secreted in response to carbachol or forskolin was acidic by approximately 0.2 pH units relative to the bath and remained acidic by approximately 0.1 pH units after bumetanide. The strong secretory response to vasoactive intestinal peptide, the acidity of [cAMP](i)-stimulated mucus, and its inhibition by bumetanide were unexpected.