Preston Manwaring

Sensitivity study of an ultrasound coupled transrectal electrical impedance tomography system for prostate imaging

In 2009, prostate cancer ranked as the most common cancer and the second most fatal cancer in men in the United States. Unfortunately, the current clinical diagnostic methods (e.g. prostate-specific antigen (PSA), digital rectal examination, endorectal MRI, transrectal ultrasound, biopsy) used for detecting and staging prostate cancer are limited. It has been shown that cancerous prostate tissue has significantly different electrical properties when compared to benign tissues. Based on these electrical property findings, a transrectal electrical impedance tomography (TREIT) system is proposed as a novel prostate imaging modality. The TREIT system comprises an array of electrodes interfaced with a clinical transrectal ultrasound (TRUS) probe. We evaluate this imaging system through a series of phantom imaging experiments to assess the systems ability to image high and low contrast objects at various positions. We found that the TREIT system can easily discern high contrast inclusions of 1 cm in diameter at distances centered at two times the radius of the TREIT probe away from the probe surface. Furthermore, this technologys ability to detect low contrast inclusions suggests that it has the potential to successfully detect prostate cancer.

3D electric impedance tomography reconstruction on multi-core computing platforms

This manuscript presents results relative to the optimization of 3D impedance tomography reconstruction algorithms for execution on multi-core computing platforms. Speed-ups obtainable by the use of modern computing architectures and by an optimized implementation allow the use of much finer FEM meshes in the forward model, leading ultimately to a better image quality.

Intracranial electrical impedance tomography: a method of continuous monitoring in an animal model of head trauma.

BACKGROUND:Electrical impedance tomography (EIT) is a method that can render continuous graphical cross-sectional images of the brain’s electrical properties. Because these properties can be altered by variations in water content, shifts in sodium concentration, bleeding, and mass deformation, EIT has promise as a sensitive instrument for head injury monitoring to improve early recognition of deterioration and to observe the benefits of therapeutic intervention. This study presents a swine model of head injury used to determine the detection capabilities of an inexpensive bedside EIT monitoring system with a novel intracranial pressure (ICP)/EIT electrode combination sensor on induced intraparenchymal mass effect, intraparenchymal hemorrhage, and cessation of brain blood flow. Conductivity difference images are shown in conjunction with ICP data, confirming the effects. METHODS:Eight domestic piglets (3–4 weeks of age, mean 10 kg), under general anesthesia, were subjected to 4 injuries: induced intraparenchymal mass effect using an inflated, and later, deflated 0.15-mL Fogarty catheter; hemorrhage by intraparenchymal injection of 1-mL arterial blood; and ischemia/infarction by euthanasia. EIT and ICP data were recorded 10 minutes before inducing the injury until 10 minutes after injury. Continuous EIT and ICP monitoring were facilitated by a ring of circumferentially disposed cranial Ag/AgCl electrodes and 1 intraparenchymal ICP/EIT sensor electrode combination. Data were recorded at 100 Hz. Two-dimensional tomographic conductivity difference (&Dgr;&sgr;) images, rendered using data before and after an injury, were displayed in real time on an axial circular mesh. Regions of interest (ROI) within the images were automatically selected as the upper or lower 5% of conductivity data depending on the nature of the injury. Mean &Dgr;&sgr; within the ROIs and background were statistically analyzed. ROI &Dgr;&sgr; was compared with the background &Dgr;&sgr; after an injury event using an unpaired, unequal variance t test. Conductivity change within an ROI after injury was likewise compared with the same ROI before the injury making use of unpaired t tests with unequal variance. RESULTS:Eight animal subjects were studied, each undergoing 4 injury events including euthanasia. Changes in conductivity due to injury showed expected pathophysiologic effects in an ROI identified within the middle of the left hemisphere; this localization is reasonable given the actual site of injury (left hemisphere) and spatial warping associated with estimating a 3-dimensional conductivity distribution in 2-dimensional space. Results are shown as mean ± 1 SD. When averaged across all 8 animals, balloon inflation caused the mean &Dgr;&sgr; within the ROI to shift by −11.4 ± 10.9 mS/m; balloon deflation by +9.4 ± 8.8 mS/m; blood injection by +19.5 ± 11.5 mS/m; death by −12.6 ± 13.2 mS/m. All induced injuries were detectable to statistical significance (P < 0.0001). CONCLUSION:This study confirms that the bedside EIT system with ICP/EIT combination sensor can detect induced trauma. Such a technique may hold promise for further research in the monitoring and management of traumatically brain-injured individuals.

Electrical property-based biopsy for prostate cancer detection and assessment

Prostate cancer diagnosis is based solely on biopsy-based findings. Unfortunately, routine biopsy protocols only sample ~0.95% of the entire gland limiting the techniques sensitivity to cancer detection. Previous studies have demonstrated significant electrical property differences between malignant and benign prostate tissues due to their dissimilar morphological architectures. We have taken the important step of translating these findings to the clinic by integrating an electrical property sensor into the tip of a standard biopsy needle. This novel device allows clinicians to simultaneously extract a tissue core and assess the electrical properties around the needle tip in real-time. The expected volume of tissue sensed with this device was estimated using finite-element method (FEM) based simulations to model the potential fields and current distributions. Prototype devices have been constructed and evaluated in a series of saline baths in order to validate the FEM-based findings. Simulations suggest that the electrical property sensor is able to interrogate a tissue volume of ~62.1 mm3 and experimental results demonstrated a volume of sensitivity of ~68.7 mm3. This coupled device is being used to assess the increased sensitivity and specificity to cancer detection when electrical properties are sensed in concert with tissue core extraction in a series of 50 ex vivo prostates. Typical 12-core prostate biopsy protocols extract a total tissue volume of 228 mm3 for histological assessment. Employing this electrical property sensor to gauge electrical properties at both the beginning and end of the needle trajectory will provide pathological assessment of an additional 1648 mm3 of tissue.

Ferromagnetic Heating for Vessel Sealing and Division Utility and Comparative Study to Ultrasonic and Bipolar Technologies

Introduction. Vessel sealing technologies have improved surgical efficiency and outcomes. Ferromagnetic technology has potential utility in this area. The aim of this study was to evaluate ferromagnetic heating in sealing and dividing vessels. Methods. A novel ferromagnetic (FM) sealer, FMsealer, was developed for sealing and dividing vessels. Using a swine in vivo model, the following endpoints were evaluated: (1) proof of concept, (2) 21-day survival surgery, and (3) comparison with ultrasonic (US) and/or bipolar (BP) devices for subjective outcomes. Seal burst strengths were measured in vitro. Mann-Whitney and Student’s t test were used. Results. After showing proof of concept, 5 swine underwent survival splenectomy, nephrectomy, hysterectomy, and mesenteric vessel division (arteries ranging from 1 to 7 mm in diameter) with necropsy after day 21 showing no evidence of surgical site bleeding. FM was equivalent to BP in tissue retention and superior to BP in spread/tissue desiccation, sticking, and charring (P ≤ .01). The FM was superior to US and BP in speed of 10 cm mesentery division (mean ± SD seconds): FM (12.9 ± 1.0 seconds), US (23.3 ± 4.4 seconds), BP (46.1 ± 5.2 seconds) (P ≤ .01 FM vs US or BP). Seal burst strength and success of sealing a 5-mm carotid artery were as follows (mean ± SD mmHg, % success burst strength >240 mm Hg): FM (710 ± 206 mm Hg, 94% success), US (848 ± 565 mm Hg, 79%), and BP (619 ± 373 mm Hg, 83%). Conclusion. Ferromagnetic heating is an effective and efficient technology for sealing and dividing of vessels. An initial prototype of the FMsealer compared favorably with commercially available products based on ultrasonic and bipolar technologies.

A modified electrode configuration for brain EIT

Electrical impedance tomography (EIT) of the brain holds great promise for long term non-ionizing detection and imaging of blood flow, ischemia, stroke, and even neuronal activity. One of the most difficult challenges with this modality, however, is overcoming the high impedance of the skull, which severely limits current passage through the intracranial space and washes out the tissue property images. There are situations, however, in which invasive electrode configurations are appropriate to overcome this limitation. We propose the use of a central and circumferential-electrode configuration to improve detection and localization of edema, hemorrhage, and ischemia within the cranium. Results from a simulation study and a phantom experiment verifying the simulation are shown.

Arbitrary geometry patient interfaces for breast cancer detection and monitoring with electrical impedance tomography

Electrical impedance tomography (EIT) is a promising technology enabling the detection or observation of many biological processes. This is typically accomplished by applying currents at known locations on an outer surface (in this case skin) and measuring voltages at other locations. This information is then used to determine electrical properties of tissue found between the electrodes by solving the associated Laplace equation. Such problems depend upon knowing the exact boundary conditions (BC). Unfortunately BCs are not always easily determined and approximations are accepted out of necessity due to problem complexity or time constraints. The EIT group at Dartmouth College has developed two new patient interfaces for breast cancer detection and monitoring both of which speed acquisition time and allow for precision BC information in natural and arbitrary geometries. Preliminary experimental results are presented.

Validation of a Laparoscopic Ferromagnetic Technology-based Vessel Sealing Device and Comparative Study to Ultrasonic and Bipolar Laparoscopic Devices

Introduction: Ferromagnetic heating is a new electrosurgery energy modality that has proven effective in hemostatic tissue dissection as well as sealing and dividing blood vessels and vascularized tissue. The purpose of this study was to evaluate a ferromagnetic-based laparoscopic vessel sealing device with respect to sealing and dividing vessels and vascularized tissue and to compare performance against current vessel sealing technologies. Materials and Methods: A laparoscopic vessel sealing device, Laparoscopic FMsealer (LFM), was studied for efficacy in sealing and dividing blood vessels and comparative studies against predicate ultrasonic, Harmonic Ace+(US), and/or bipolar, LigaSure 5 mm Blunt Tip and/or Maryland (BP), devices in vivo using a swine model and in vitro for comparison of seal burst pressure and reliability. Mann-Whitney and Student t test were used for statistical comparisons. Results: In division of 10 cm swine small bowel mesentery in vivo, the laparoscopic FMsealer [12.4±1.8 sec (mean±SD)], was faster compared with US (26.8±2.5 s) and BP (30.0±2.7 s), P<0.05 LFM versus US and BP. Blinded histologic evaluation of 5 mm vessel seals in vivo showed seal lateral thermal spread to be superior in LFM (1678±433 &mgr;m) and BP (1796±337 &mgr;m) versus US (2032±387 &mgr;m), P<0.001. In vitro, seal burst strength and success of sealing 2 to 4 mm arteries were as follows (mean±SD mm Hg, % success burst strength >240 mm Hg): LFM (1079±494 mm Hg, 98.1% success) versus BP (1012±463, 99.0%), P=NS. For 5 to 7 mm arteries: LFM (1098±502 mm Hg, 95.3% success) versus BP (715±440, 91.8%), P<0.001 in burst strength and P=NS in % success. Five 60 kg female swine underwent 21-day survival studies following ligation of vessels ranging from 1 to 7 mm in diameter (n=186 total vessels). Primary seal was successful in 97%, 99% including salvage seals. There was no evidence of postoperative bleeding at sealed vessels at 21-day necropsy. Conclusion: The Laparoscopic FMsealer is an effective tool for sealing and dividing blood vessels and vascularized tissue and compares favorably to current technologies in clinically relevant end points.

Sensitivity study of an ultrasound coupled transrectal electrical Impedance Tomography system for prostate imaging

In 2009, prostate cancer ranks as the most common cancer and the second most fatal cancer in men in the United States. Unfortunately, the current clinical diagnostic methods (e.g. prostate-specific antigen (PSA), digital rectal examination, endorectal MRI, transrectal ultrasound, biopsy) used for detecting and staging prostate cancer are limited. It has been shown that cancerous prostate tissue has significantly different electrical properties when compared to benign tissues. Based on these electrical property findings, a TransRectal Electrical Impedance Tomography (TREIT) system is proposed as a novel prostate imaging modality. The TREIT system is comprised of an array of electrodes interfaced with a clinical TransRectal UltraSound (TRUS) probe. We evaluate this imaging system through series of phantom imaging experiments to assess the systems ability to image high and low contrast objects at various positions. We found that the TREIT system can easily discern high contrast inclusions of 1 cm in diameter at distances centered at 2 times the radius of the TREIT probe away from the probe surface. Furthermore, this technologys ability to detect low contrast inclusions suggests that it has the potential to successfully detect prostate cancer.

Chemotherapy Monitoring With EIS: Early Findings

We are currently imaging women undergoing neoadjuvant chemotherapy for the treatment of breast cancer. Patients with palpable tumors are recruited by our participating oncologists to undergo chemotherapy prior to tumor resection. Treatment plans timing and duration vary based on the protocol selected for a specific patient. However, in all cases, treatments consist of several sessions of chemotherapy prior to tumor resection surgery. Typically, patients are imaged on the days of their treatments, just before infusion. The final imaging session is scheduled to take place on the day of surgery. To date we have imaged 8 patients multiple times and are able to compare changes between sessions with some of these patients. Using our latest 3D reconstruction algorithm, we have found a correlation between the response of the patients as established in pathology, following surgery, and the apparent shrinkage of the volume of tissue above 90% of maximum conductivity. This correlation between the reconstructed data and the findings in pathology would indicate the usefulness of EIS in monitoring the response to chemotherapy.