Image Feedback Research Articles

Low-Cost and Easily Fabricated Ultrasound-Guided Breast Phantom for Breast Biopsy Training

We aimed to develop an inexpensive and easy-to-fabricate gelatin-based training phantom for improving the breast biopsy skill and confidence level of residents. Young’s modulus and acoustic properties of the gelatin tissue phantom and simulated tumors were investigated. Six residents were requested to evaluate the effectiveness of the breast phantom. The results showed that 83% (n = 5) of the participants agreed that the ultrasound image quality produced by the breast phantom was excellent or good. Only 17% (n = 1) of the participants claimed that there was room for improvement for the haptic feedback they received during the placement of the core needle into the breast phantom. The mean pre-instructional score was 17% (SD 17%) for all participants. The mean post-instructional score was 83% (SD 17%), giving an overall improvement of 67%. In conclusion, the mean needle biopsy skill and confidence levels of the participants substantially increased through simulation training on our breast phantom. The participants’ feedback showed the phantom is sufficiently realistic in terms of ultrasound imaging and haptic feedback during needle insertion; thus, the training outcome can be linked to the performance of residents when they perform a live biopsy.

Dual Ultrasound and Photoacoustic Tracking of Magnetically Driven Micromotors: From In Vitro to In Vivo.

The fast evolution of medical micro- and nanorobots in the endeavor to perform non-invasive medical operations in living organisms has boosted the use of diverse medical imaging techniques in the last years. Among those techniques, photoacoustic imaging (PAI), considered a functional technique, has shown to be promising for the visualization of micromotors in deep tissue with high spatiotemporal resolution as it possesses the molecular specificity of optical methods and the penetration depth of ultrasound. However, the precise maneuvering and function's control of medical micromotors, in particular in living organisms, require both anatomical and functional imaging feedback. Therefore, herein, the use of high-frequency ultrasound and PAI is reported to obtain anatomical and molecular information, respectively, of magnetically-driven micromotors in vitro and under ex vivo tissues. Furthermore, the steerability of the micromotors is demonstrated by the action of an external magnetic field into the uterus and bladder of living mice in real-time, being able to discriminate the micromotors' signal from one of the endogenous chromophores by multispectral analysis. Finally, the successful loading and release of a model cargo by the micromotors toward non-invasive in vivo medical interventions is demonstrated.

Image-Guided Control of an Endoscopic Robot for OCT Path Scanning

Optical coherence tomography (OCT) endoscopic catheters provide efficient solutions for the non-invasive scan of malignant tissues in internal human organs. In this letter, we investigate the image-guided control of a robotic flexible endoscopic system equipped with an OCT probe for autonomous tissue scanning. The visual control strategy is achieved by combining the image feedback from both a monocular endoscopic camera (eye-to-hand) and an OCT probe (eye-in-hand). Our control strategy allows the OCT probe to automatically track a trajectory defined by the user on the 2D endoscopic image and keep contact with the scanned surface. The orientation, depth, and endoscopic 2D image position are controlled by solving an optimization problem, which is converted to a quadratic programming problem. For the implementation of the visual control strategy, we also consider visibility constraints and actuators limitations. In addition, a marker-based method to estimate the 3D pose of the continuum robot using only 2D images is proposed based on a Kalman filter and a registration technique. The proposed control strategy is validated using both simulation and laboratory experiments.

Functional Neuroimaging During Asleep DBS Surgery: A Proof of Concept Study.

Object: A real-time functional magnetic resonance imaging (fMRI) feedback during ventral intermediate nucleus (VIM) deep brain stimulation (DBS) under general anesthesia (or “asleep” DBS) does not exist. We hypothesized that it was feasible to acquire a reliable and responsive fMRI during asleep VIM DBS surgery.Methods: We prospectively enrolled 10 consecutive patients who underwent asleep DBS for the treatment of medication-refractory essential tremor. Under general anesthesia, we acquired resting-state functional MRI immediately before and after the cannula insertion. Reliability was determined by a temporal signal-to-noise-ratio >100. Responsiveness was determined based on the fMRI signal change upon insertion of the cannula to the VIM.Results: It was feasible to acquire reliable fMRI during asleep DBS surgery. The fMRI signal was responsive to the brain cannula insertion, revealing a reduction in the tremor network's functional connectivity, which did not reach statistical significance in the group analysis.Conclusions: It is feasible to acquire a reliable and responsive fMRI signal during asleep DBS. The acquisition steps and the preprocessing pipeline developed in these experiments will be useful for future investigations to develop fMRI-based feedback for asleep DBS surgery.

Neural network‐assisted robotic vision system for industrial applications

AbstractThis paper investigates the performance of neural networks in positioning an industrial robot manipulator based on image feedback. Visual servoing regulates the pose of the robot manipulator in accordance with the target image data. As the servoing proceeds, the end‐effector positions to its final pose as the image feature error exponentially decreases to zero. In this paper, the trained network moves the robot manipulator from an arbitrary initial pose to an intermediate posture based on the reference image features given. Then, fine‐tuning based on the traditional visual servoing method is performed to achieve an accurate pick‐and‐place task with minimum iterations. The experimental results prove the capability of the neural network architectures to predict the desired pose using local image descriptor, corner points. This paper investigates the performance of two neural network designs applied to visual positioning and compares them with the traditional image‐based visual servoing (IBVS) method in terms of execution time.

Holographic Display-Based Control for High-Accuracy Photolithography of Cellular Micro-Scaffold With Heterogeneous Architecture

Engineered three-dimensional (3D) tissues that replicate composite in-vivo architectures have shown great potential for use in biomedical research. Cell-encapsulated hydrogel micro-scaffolds have been applied widely as basic building blocks to construct these artificial tissues. However, accurate reproduction of heterogeneous hierarchical structures and different regional mechanical properties inside a single integrated micro-scaffold that mimics physiologically relevant complex tissues presents a major challenge. Here, we propose a novel fabrication control algorithm to achieve high-accuracy photolithography of micro-scaffolds that recapitulate the high fidelity of native tissues by adjusting a 3D digital mask using holographic imaging feedback. By performing digital holographic reconstruction to express the hydrogel photocuring process in a matrix form and presetting the curing duration for each discrete point, the 3D digital mask was predefined to represent the required customized micro-scaffold. During fabrication, the UV exposure area was divided into microscaled grids with relatively uniform irradiance to control the photocuring process discretely for every local region in the entire architecture. The holographic imaging feedback allowed the curing duration of each grid to be adjusted in real-time, which enabled accurate reproduction of a 3D construct integrated with different microstructural morphologies and mechanical properties. Finally, PEGDA and GelMA, as typical biomaterials, were used to fabricate the heterogeneous hierarchical micro-scaffold. The structural accuracy was improved from 65 m to 12 m and the Youngs modulus was controlled flexibly in the 27.93.5 to 91.23.5 kPa range. With different local mechanical properties, cell migration in the micro-scaffold from soft to stiff areas is observed successfully.

‘When the picture does not really tell the story’– A qualitative exploration of the MRI report of findings as a means for generating shared diagnostic meaning during the management of patients suffering from persistent spinal pain

ObjectivesTo explore the magnetic resonance imaging (MRI) feedback report as a health care encounter for generating shared diagnostic meaning. MethodsAn exploratory, qualitative case study was conducted using video observation of the MRI report of findings, individual face-to-face and telephonic interviews. ResultsFrom fourteen distinct encounters, three key themes emerged, these being: ‘a powerful shared experience, ‘a legacy of biomedical thinking’ and ‘clinical practice quandaries’. Generally speaking, the MRI encounter was observed to be both an effective and satisfying method for developing shared diagnostic meaning. However, in instances where a structure-based diagnosis could not be reasonably established, clinicians experienced doubts in what to present in a ‘soft report’. A feature of these was the communication of speculative causal feedback, based on non-visualised structures and/or incidental findings observed. ConclusionShared diagnostic meaning can result from a ‘soft’ MRI report of findings. However, the emergence of diagnostic closure is not guaranteed. Further exploration of this phenomenon in the context of shared decision making and the therapeutic alliance is warranted. Practice implicationsPre-feedback peer conferences might be considered in order to standardise the information communicated to patients. Clinicians might also consider limiting the MRI scan as a visual aid in ‘soft’ reports.

A novel multi-DoF surgical robotic system for brachytherapy on liver tumor: Design and control

PurposeRadioactive seed implantation is an effective invasive treatment method for malignant liver tumors in hepatocellular carcinomas. However, challenges of the manual procedure may degrade the efficacy of the technique, such as the high accuracy requirement and radiation exposure to the surgeons. This paper aims to develop a robotic system and its control methods for assisting surgeons on the treatment.MethodWe present an interventional robotic system, which consists of a 5 Degree-of-Freedom (DoF) positioning robotic arm (a 3-DoF translational joint and a 2-DoF revolute joint) and a needle actuator used for needle insertion and radioactive seeds implantation. Control strategy is designed for the system to ensure the safety of the motion. In the designed framework, an artificial potential field (APF)-based motion planning and an ultrasound (US) image-based contacting methods are proposed for the control.ResultExperiments were performed to evaluate position and orientation accuracy as well as validate the motion planning procedure of the system. The mean and standard deviation of targeting error is 0.69 mm and 0.33 mm, respectively. Needle placement accuracy is 1.10 mm by mean. The feasibility of the control strategy, including path planning and the contacting methods, is demonstrated by simulation and experiments based on an abdominal phantom.ConclusionThis paper presents a robotic system with force and US image feedback in assisting surgeons performing brachytherapy on liver tumors. The proposed robotic system is capable of executing an accurate needle insertion task with by optical tracking. The proposed methods improve the safety of the robot’s motion and automate the process of US probe contacting under the feedback of US-image.

Robotic Ultrasound Scanning With Real-Time Image-Based Force Adjustment: Quick Response for Enabling Physical Distancing During the COVID-19 Pandemic.

During an ultrasound (US) scan, the sonographer is in close contact with the patient, which puts them at risk of COVID-19 transmission. In this paper, we propose a robot-assisted system that automatically scans tissue, increasing sonographer/patient distance and decreasing contact duration between them. This method is developed as a quick response to the COVID-19 pandemic. It considers the preferences of the sonographers in terms of how US scanning is done and can be trained quickly for different applications. Our proposed system automatically scans the tissue using a dexterous robot arm that holds US probe. The system assesses the quality of the acquired US images in real-time. This US image feedback will be used to automatically adjust the US probe contact force based on the quality of the image frame. The quality assessment algorithm is based on three US image features: correlation, compression and noise characteristics. These US image features are input to the SVM classifier, and the robot arm will adjust the US scanning force based on the SVM output. The proposed system enables the sonographer to maintain a distance from the patient because the sonographer does not have to be holding the probe and pressing against the patient's body for any prolonged time. The SVM was trained using bovine and porcine biological tissue, the system was then tested experimentally on plastisol phantom tissue. The result of the experiments shows us that our proposed quality assessment algorithm successfully maintains US image quality and is fast enough for use in a robotic control loop.

Silk Fibroin Coated Magnesium Oxide Nanospheres: A Biocompatible and Biodegradable Tool for Noninvasive Bioimaging Applications.

Fluorescent nanoparticles (NPs) have been increasingly studied as contrast agents for better understanding of biological processes at the cellular and molecular level. However, their use as bioimaging tools is strongly dependent on their optical emission as well as their biocompatibility. This work reports the fabrication and characterization of silk fibroin (SF) coated magnesium oxide (MgO) nanospheres, containing oxygen, Cr3+ and V2+ related optical defects, as a nontoxic and biodegradable hybrid platform for bioimaging applications. The MgO-SF spheres demonstrated enhanced emission efficiency compared to noncoated MgO NPs. Furthermore, SF sphere coating was found to overcome agglomeration limitations of the MgO NPs. The hybrid nanospheres were investigated as an in vitro bioimaging tool by recording their cellular uptake, trajectories, and mobility in human skin keratinocytes cells (HaCaT), human glioma cells (U87MG) and breast cancer cells (MCF7). Enhanced cellular uptake and improved intracellular mobilities of MgO-SF spheres compared to MgO NPs was demonstrated in three different cell lines. Validated infrared and bright emission of MgO-SF NP indicate their prospects for in vivo imaging. The results identify the potential of the hybrid MgO-SF nanospheres for bioimaging. This study may also open new avenues to optimize drug delivery through biodegradable silk and provide noninvasive functional imaging feedback on the therapeutic processes through fluorescent MgO.

Immediate effect of neurofeedback training on the pain matrix and cortical areas involved in processing neuropsychological functions.

This study investigated the impact of neurofeedback training on the deeper cortical structures that comprise the "pain matrix" and are involved in processing neuropsychological functions. Five paraplegic patients with central neuropathic pain received up to 40 sessions of neurofeedback training. They were asked to simultaneously modulate the relative power of the theta, alpha and beta bands, provided as a feedback from the sensorimotor cortex. The source localization technique was applied on EEG data recorded with 16 electrodes placed over the whole head. Neurofeedback training from the sensorimotor cortex induced effects on the pain matrix and in the areas involved in processing neuropsychological functions such as memory, executive functions and emotional regulations. Alpha and beta band activity was most increased in insular, cingulate and frontal cortex regions, and other areas corresponding to executive and emotional function processing. Theta band decreases were noted in the frontal, cingulate and motor cortices. In group analysis, theta and beta band activity was significantly reduced. The single channel electroencephalogram-based neurofeedback training produced effects on similar areas that are targeted in 19 channels standardized low-resolution brain electromagnetic tomography and expensive time-delayed functional magnetic resonance imaging feedback studies.

Medication-Related Osteonecrosis of the Jaw (MRONJ): Are Antiresorptive Drugs the Main Culprits or Only Accomplices? The Triggering Role of Vitamin D Deficiency.

Osteonecrosis of the jaw (ONJ) is a severe clinical condition characterized mostly but not exclusively by an area of exposed bone in the mandible and/or maxilla that typically does not heal over a period of 6–8 weeks. The diagnosis is first of all clinical, but an imaging feedback such as Magnetic Resonance is essential to confirm clinical suspicions. In the last few decades, medication-related osteonecrosis of the jaw (MRONJ) has been widely discussed. From the first case reported in 2003, many case series and reviews have appeared in the scientific literature. Almost all papers concerning this topic conclude that bisphosphonates (BPs) can induce this severe clinical condition, particularly in cancer patients. Nevertheless, the exact mechanism by which amino-BPs would be responsible for ONJ is still debatable. Recent findings suggest a possible alternative explanation for BPs role in this pattern. In the present work we discuss how a condition of osteomalacia and low vitamin D levels might be determinant factors.

Psychological Impact of Pro-Anorexia and Pro-Eating Disorder Websites on Adolescent Females: A Systematic Review.

(1) Background: Teenagers (in particular, females) suffering from eating disorders report being not satisfied with their physical aspect and they often perceive their body image in a wrong way; they report an excessive use of websites, defined as PRO-ANA and PRO-MIA, that promote an ideal of thinness, providing advice and suggestions about how to obtain super slim bodies. (2) Aim: The aim of this review is to explore the psychological impact of pro-ana and pro-mia websites on female teenagers. (3) Methods: We have carried out a systematic review of the literature on PubMed. The search terms that have been used are: “Pro” AND “Ana” OR “Blogging” AND “Mia”. Initially, 161 publications were identified, but in total, in compliance with inclusion and exclusion criteria, 12 studies have been analyzed. (4) Results: The recent scientific literature has identified a growing number of Pro Ana and Pro Mia blogs which play an important role in the etiology of anorexia and bulimia, above all in female teenagers. The feelings of discomfort and dissatisfaction with their physical aspect, therefore, reduce their self-esteem. (5) Conclusion: These websites encourage anorexic and bulimic behaviors, in particular in female teenagers. Attention to healthy eating guidelines and policies during adolescence, focused on correcting eating behavioral aspects, is very important to prevent severe forms of psychopathology with more vulnerability in the perception of body image, social desirability, and negative emotional feedback.

Closed-Loop neuromodulation for clustering neuronal populations.

Pathological synchronization of neurons is associated with symptoms of movement disorders, such as Parkinson's disease and essential tremor. High-frequency deep brain stimulation (DBS) suppresses symptoms, presumably through the desynchronization of neurons. Coordinated reset (CR) delivers trains of high-frequency stimuli to different regions in the brain through multiple electrodes and may have more persistent therapeutic effects than conventional DBS. As an alternative to CR, we present a closed-loop control setup that desynchronizes neurons in brain slices by inducing clusters using a single electrode. Our setup uses calcium fluorescence imaging to extract carbachol-induced neuronal oscillations in real time. To determine the appropriate stimulation waveform for inducing clusters in a population of neurons, we calculate the phase of the neuronal populations and then estimate the phase response curve (PRC) of those populations to electrical stimulation. The phase and PRC are then fed into a control algorithm called the input of maximal instantaneous efficiency (IMIE). By using IMIE, the synchrony across the slice is decreased by dividing the population of neurons into subpopulations without suppressing the oscillations locally. The desynchronization effect is persistent 10 s after stimulation is stopped. The IMIE control algorithm may be used as a novel closed-loop DBS approach to suppress the symptoms of Parkinson's disease and essential tremor by inducing clusters with a single electrode.NEW & NOTEWORTHY Here, we present a closed-loop controller to desynchronize neurons in brain slices by inducing clusters using a single electrode using calcium imaging feedback. Phase of neurons are estimated in real time, and from the phase response curve stimulation is applied to achieve target phase differences. This method is an alternative to coordinated reset and is a novel therapy that could be used to disrupt synchronous neuronal oscillations thought to be the mechanism underlying Parkinson's disease.

Feedback Control for the Precise Shape Morphing of 4D-Printed Shape Memory Polymer

Four-dimensional printing (4DP) is a newly emerged technology that uses smart materials for additive manufacturing and thus enables shape and/or property change upon stimulus after the printing process. Present study on 4DP has been focused on open-loop stimulus, which can hardly ensure high shape precision and predictable final states. In this article, a new closed-loop 4DP (CL4DP) process supplementing 4D printed actuation with closed loop control methods is proposed. Image feedback is used for enhancing the conventional open loop 4DP morphing process and a controller is implemented to regulate the intensity of the stimulus accordingly in real-time. To achieve precise control, a nonlinear affine system model is built by model identification with measurement data to describe the dynamic shape recovery process of the 4D-printed shape memory polymer (SMP). Precise shape control is achieved and the effects of controller parameters on the precision of CL4DP are studied. Traditionally, SMP has a discrete number of selected steady states. With CL4DP, such steady states can be continuous and arbitrary.

Optimal Design and Implementation of a Novel Two-Dimensional Electromagnetic Navigation System That Allows Focused Heating of Magnetic Nanoparticles

A magnetic drug-targeting system featuring real-time imaging, guidance, and local heating is required for more precise drug targeting and minimization of side effects. In this article, we present a novel electromagnetic navigation and heating system that not only guides and navigates magnetic nanoparticles (MNPs) with real-time imaging feedback, but also uses focused MNP heating to release drugs while monitoring the temperature. The magnetic field amplitude and magnetic gradient play key roles in our integrated system; we enhanced the gradient and field within a field of view of 30 × 30 mm. Performance was examined via simulation employing COMSOL Multiphysics software and verified experimentally. After optimization, the maximum gradients attained on the x and y axes are 4.15 and 2.23 T/m/μ0, respectively, for the electromagnetic actuator mode, and 8.48 T/m/μ0 for the magnetic particle imaging mode. The magnetic field amplitude for heating was 19.70 mT at 100 kHz. We then built a two-dimensional MNPs navigation/heating system to demonstrate the in vitro feasibility of our scheme; this afforded a 1-Hz navigation update rate during MNPs guidance in a Y-shaped channel and locally heated MNPs with temperature monitoring.

A preclinical study of diffusion-weighted MRI contrast as an early indicator of thermal ablation.

Intraoperative T2 -weighted (T2-w) imaging unreliably captures image contrast specific to thermal ablation after transcranial MR-guided focused ultrasound surgery, impeding dynamic imaging feedback. Using a porcine thalamotomy model, we test the unproven hypothesis that intraoperative DWI can improve dynamic feedback by detecting lesioning within 30 minutes of transcranial MR-guided focused ultrasound surgery. Twenty-five thermal lesions were formed in six porcine models using a clinical transcranial MR-guided focused ultrasound surgery system. A novel diffusion-weighted pulse sequence monitored the formation of T2-w and diffusion-weighted lesion contrast after ablation. Using postoperative T2-w contrast to indicate lesioning, apparent intraoperative image contrasts and diffusion coefficients at each lesion site were computed as a function of time after ablation, observed peak temperature, and observed thermal dose. Lesion sizes segmented from imaging and thermometry were compared. Image reviewers estimated the time to emergence of lesion contrast. Intraoperative image contrasts were analyzed using receiver operator curves. On average, the apparent diffusion coefficient at lesioned sites decreased within 5 minutes after ablation relative to control sites. In-plane lesion areas on intraoperative DWI varied from postoperative T2-w MRI and MR thermometry by mm2 and mm2 , respectively. The 0.25, 0.5, and 0.75 quantiles of the earliest times of observed T2-w and diffusion-weighted lesion contrast were 10.7, 21.0, and 27.8 minutes and 3.7, 8.6, and 11.8 minutes, respectively. The T2-w and diffusion-weighted contrasts and apparent diffusion coefficient values produced areas under the receiver operator curve of 0.66, 0.80, and 0.74, respectively. Intraoperative DWI can detect MR-guided focused ultrasound surgery lesion formation in the brain within several minutes after treatment.

Effect of uncertainties in quantitative 18 F-FDG PET/CT imaging feedback for intratumoral dose-response assessment and dose painting by number.

Intratumoral dose response can be detected using serial fluoro-2-deoxyglucose-(FDG) positron emission tomography (PET)/computed tomography (CT) imaging feedback during treatment and used to guide adaptive dose painting by number (DPbN). However, to reliably implement this technique, the effect of uncertainties in quantitative PET/CT imaging feedback on tumor voxel dose-response assessment and DPbN needs to be determined and reduced. Three major uncertainties, induced by (a) PET imaging partial volume effect (PVE) and (b) tumor deformable image registration (DIR), and (c) variation of the time interval between FDG injection and PET image acquisition (TI), were determined using serial FDG-PET/CT images acquired during chemoradiotherapy of 18 head and neck cancer patients. PET imaging PVE was simulated using the discrepancy between with and without iterative deconvolution-based PVE corrections. Effect of tumor DIR uncertainty was simulated using the discrepancy between two DIR algorithms, including one with and one without soft-tissue mechanical correction for the voxel displacement. The effect of TI variation was simulated using linear interpolation on the dual-point PET/CT images. Tumor voxel pretreatment metabolic activity (SUV0 ) and dose-response matrix (DRM) discrepancies induced by each of the three uncertainties were quantified, respectively. Adverse effects of tumor voxel SUV0 and DRM discrepancies on tumor control probability (TCP) in DPbN were assessed. Partial volume effect and TI variations of 10 mins induced a mean±standard deviation (SD) of tumor voxel SUV0 discrepancies to be -0.7%±9.2% and 0%±4.8%, respectively. Tumor voxel DRM discrepancies induced by PVE, tumor DIR discrepancy, and TI variations were 0.6%±8.9%, 1.7%±9.1%, and 0%±7%, respectively. Partial volume effect induced SUV0 and DRM discrepancies correlated significantly with the tumor shape and FDG uptake heterogeneity. Tumor DIR uncertainty-induced DRM discrepancy correlated significantly with the tumor volume and shrinkage during treatment. Among the three uncertainties, PVE dominated the adverse effects on the TCP, with a mean±SD of TCP reduction to be 12.7%±9.8% for all tumors if no compensation was applied for. Effect of uncertainties in quantitative FDG-PET/CT imaging feedback on intratumoral dose-response quantification was not negligible. These uncertainties primarily caused by PVE and tumor DIR were highly dependent on individual tumor shape, volume, shrinkage during treatment, and pretreatment SUV heterogeneity, which can be managed individually. The adverse effects of these uncertainties could be minimized by using proper PVE corrections and DIR methods and compensated for in the clinical implementation of DPbN.

Inter/intra-tumoral dose response variations assessed using FDG-PET/CT feedback images: Impact on tumor control and treatment dose prescription

PurposeTo quantify inter/intra-tumoral variations of baseline metabolic activity and dose response. To evaluate their impact on tumor control and treatment dose prescription strategies. Methods and materialsTumor voxel baseline metabolic activity, SUV0, and dose response matrix, DRM, quantified using the pre-treatment and weekly FDG-PET/CT imaging feedback for each of 34 HNSCC patients (25 HPV+ and 9 HVP−) were evaluated. Inter/intra-tumoral variations of tumor voxel (SUV0, DRM) for each of the HPV− and HPV+ tumor groups were quantified and used to evaluate the variations of individual tumor control probabilities and the efficiency of uniform vs non-uniform treatment dose prescription strategies. ResultsTumor voxel dose response variation of all tumor voxels assessed using FDG-PET/CT imaging feedback had the mean(CV) = 0.47(47%), which was consistent with those of previously published in vitro tumor clonogenic assay. The HPV− tumors had the mean(CV) dose response, 0.53(49%), significantly larger than those of the HPV+ tumors, 0.45(43%). However, their baseline SUVs were opposite, 6.5(56%) vs 7.7(65%). Comparing to the inter-tumoral variations, both HPV−/+ tumor groups showed larger intra-tumoral variations, (53%, 58%) vs (20%, 31%) for the baseline SUV and (38%, 37%) vs (31%, 21%) for the dose response. Due to the large dose response variations, treatment dose to control the tumor voxels has very broad range with CV of TCD50 = 97% for the HPV− and 67% for the HPV+ tumor group respectively. As a consequence, heterogeneous prescription dose could potentially reduce the treatment integral dose for 92% of the HPV+ tumors and 78% of the HPV− tumors. ConclusionsThe study demonstrates that tumor dose response assessed using FDG-PET/CT feedback images had a similar distribution to those assessed conventionally using in vitro tumor clonogenic assay. Inter-tumoral dose response variation seems larger for HPV− tumors, but intra-tumoral dose response variations are similar for both HPV groups. These variations cause very large variation on the individual tumor control probability and limit the efficacy of dose escalation and de-escalation in conventional clinical practice. On the other hand, heterogeneous dose prescription guided by metabolic imaging feedback has a potential advantage in radiotherapy.

A Direct Drive Parallel Plane Piezoelectric Needle Positioning Robot for MRI Guided Intraspinal Injection.

To improve both the procedure time and positioning accuracy, an MRI guided robotic needle positioning system is developed. The robot uses linear piezoelectric motors to directly drive a parallel plane positioning mechanism. Feedback is provided through MRI during the orientation procedure. Both accuracy and repeatability of the robot are characterized. This system is found to be capable of repeatability below 51μm. Needle endpoint error is limited by imaging modality, but is validated to 156μm. The reported robot and MRI image feedback system is capable of repeatable and accurate needle guide positioning. This high accuracy will result in a significant improvement to the workflow of spinal injection procedures.