Featured Researches

Medical Physics

3D Augmented Reality-Assisted CT-Guided Interventions: System Design and Preclinical Trial on an Abdominal Phantom using HoloLens 2

Background: Out-of-plane lesions pose challenges for CT-guided interventions. Augmented reality (AR) headset devices have evolved and are readily capable to provide virtual 3D guidance to improve CT-guided targeting. Purpose: To describe the design of a three-dimensional (3D) AR-assisted navigation system using HoloLens 2 and evaluate its performance through CT-guided simulations. Materials and Methods: A prospective trial was performed assessing CT-guided needle targeting on an abdominal phantom with and without AR guidance. A total of 8 operators with varying clinical experience were enrolled and performed a total of 86 needle passes. Procedure efficiency, radiation dose, and complication rates were compared with and without AR guidance. Vector analysis of the first needle pass was also performed. Results: Average total number of needle passes to reach the target reduced from 7.4 passes without AR to 3.4 passes with AR (54.2% decrease, p=0.011). Average dose-length product (DLP) decreased from 538 mGy-cm without AR to 318 mGy-cm with AR (41.0% decrease, p=0.009). Complication rate of hitting a non-targeted lesion decreased from 11.9% without AR (7/59 needle passes) to 0% with AR (0/27 needle passes). First needle passes were more nearly aligned with the ideal target trajectory with AR versus without AR (4.6° vs 8.0° offset, respectively, p=0.018). Medical students, residents, and attendings all performed at the same level with AR guidance. Conclusions: 3D AR guidance can provide significant improvements in procedural efficiency and radiation dose savings for targeting challenging, out-of-plane lesions. AR guidance elevated the performance of all operators to the same level irrespective of prior clinical experience.

Read more
Medical Physics

3D Fusion between Fluoroscopy Angiograms and SPECT Myocardial Perfusion Images to Guide Percutaneous Coronary Intervention

Background. Percutaneous coronary intervention(PCI) in stable coronary artery disease(CAD) is commonly triggered by abnormal myocardial perfusion imaging(MPI). However, due to the possibilities of multivessel disease and variability of coronary artery perfusion distribution, opportunity exists to better align anatomic stenosis with perfusion abnormalities to improve revascularization decisions. This study aims to develop a 3D multi-modality fusion approach to assist decision-making for PCI. Methods. Coronary arteries from fluoroscopic angiography(FA) were reconstructed into 3D artery anatomy. Left ventricular(LV) epicardial surface was extracted from SPECT. The 3D artery anatomy was non-rigidly fused with the LV epicardial surface. The accuracy of the 3D fusion was evaluated via both computer simulation and real patient data. For technical validation, simulated FA and MPI were integrated and then compared with the ground truth from a digital phantom. For clinical validation, FA and SPECT images were integrated and then compared with the ground truth from CT angiograms. Results. In the technical evaluation, the distance-based mismatch error between simulated fluoroscopy and phantom arteries is 1.86(SD:1.43)mm for left coronary arteries(LCA) and 2.21(SD:2.50)mm for right coronary arteries(RCA). In the clinical validation, the distance-based mismatch errors between the fluoroscopy and CT arteries were 3.84(SD:3.15)mm for LCA and 5.55(SD:3.64)mm for RCA. The presence of the corresponding fluoroscopy and CT arteries in the AHA 17-segment model agreed well with a Kappa value of 0.91(95% CI: 0.89-0.93) for LCA and 0.80(CI: 0.67-0.92) for RCA. Conclusions. Our fusion approach is technically accurate to assist PCI decision-making and is clinically feasible to be used in the catheterization laboratory. There is an opportunity to improve the decision-making and outcomes of PCI in stable CAD.

Read more
Medical Physics

3D Monte Carlo Simulation of Light Distribution in Mouse Brain in Quantitative Photoacoustic Computed Tomography

Photoacoustic computed tomography (PACT) detects light-induced ultrasound waves to reconstruct the optical absorption contrast of the biological tissues. Due to its relatively deep penetration (several centimeters in soft tissue), high spatial resolution, and inherent functional sensitivity, PACT has great potential for imaging mouse brains with endogenous and exogenous contrasts, which is of immense interest to the neuroscience community. However, conventional PACT either assumes homogenous optical fluence within the brain or uses a simplified attenuation model for optical fluence estimation. Both approaches underestimate the complexity of the fluence heterogeneity and can result in poor quantitative imaging accuracy. To optimize the quantitative performance of PACT, we explore for the first time 3D Monte Carlo simulation to study the optical fluence distribution in a complete mouse brain model. We apply the MCX Monte Carlo simulation package on a digital mouse (Digimouse) brain atlas that has complete anatomy information. To evaluate the impact of the brain vasculature on light delivery, we also incorporate the whole-brain vasculature in the Digimouse atlas. The simulation results clearly show that the optical fluence in the mouse brain is heterogeneous at the global level and can decrease by a factor of five with increasing depth. Moreover, the strong absorption and scattering of the brain vasculature also induce the fluence disturbance at the local level. Our results suggest that both global and local fluence heterogeneity contributes to the reduced quantitative accuracy of the reconstructed PACT images of mouse brain.

Read more
Medical Physics

3D source tracking and error detection in HDR using two independent scintillator dosimetry systems

The high dose gradients near the source characteristics of brachytherapy are equivalent to nefarious effects if unnoticed errors take place during the patient treatment. In vivo dosimetry is the only method to quantify the delivered dose. Previous studies to this one, have characterized potential detectors that can be used as in vivo dosimeter. Some of them have focused on the source tracking topic in HDR brachytherapy. The aim of this study is to perform 3D source position reconstruction by combining in vivo dosimetry measurements from two independent detector systems. The first was based on multiple (three) plastic scintillator detectors and the second on a single inorganic crystal (CsI:Tl). By combining two detector responses, we enabled the determination of the absolute source coordinates in 3D space. The method in this study proposed can be extended to the combination of different systems.

Read more
Medical Physics

A 100 ps TOF Detection System for On-Line Range- Monitoring in Hadrontherapy

The accuracy of hadrontherapy treatment is currently limited by ion-range uncertainties. In order to fully exploit the potential of this technique, we propose the development of a novel system for online control of particle therapy, based on TOF-resolved (time-of-flight) Prompt Gamma (PG) imaging with 100 ps time resolution. Our aim is to detect a possible deviation of the proton range with respect to treatment planning within the first few irradiation spots at the beginning of the session. The system consists of a diamond-based beam hodoscope for single proton tagging, operated in time coincidence with one or more gamma detectors placed downstream of the patient. The TOF between the proton time of arrival in the hodoscope and the PG detection time provides an indirect measurement of the proton range in the patient with a precision strictly related to the system time resolution. With a single ~38 cm 3 BaF2 detector placed at 15 cm from a heterogeneous PMMA target, we obtained a coincidence time resolution of 101 ps (rms). This system allowed us to measure the thickness and position of an air cavity within a PMMA target, and the associated proton range shift: a 3 mm shift can be detected at 2 σ confidence level within a single large irradiation spot (~10 8 protons). We are currently conceiving a multi-channel PG timing detector with 3D target coverage. Each pixel will provide the PG detection time and its hit position, that can be used to reconstruct the 3D distribution of PG vertices in the patient. Our approach does not require collimation and allows to dramatically increase the detection efficiency. Since both signal detection and background rejection are based on TOF, the constraints on energy resolution can be relaxed to further improve time resolution.

Read more
Medical Physics

A 3D-Hybrid-Shot Spiral Sequence for Hyperpolarized 13 C Imaging

Purpose: Hyperpolarized imaging experiments have conflicting requirements of high spatial, temporal, and spectral resolution. Spectral-Spatial RF excitation has been shown to form an attractive magnetization-efficient method for hyperpolarized imaging, but the optimum readout strategy is not yet known. Methods: In this work we propose a novel 3D hybrid-shot spiral sequence which features two constant density regions that permit the retrospective reconstruction of either high spatial or high temporal resolution images post hoc, (adaptive spatiotemporal imaging) allowing greater flexibility in acquisition and reconstruction. Results: We have implemented this sequence, both via simulation and on a pre-clinical scanner, to demonstrate its feasibility, in both a 1H phantom and with hyperpolarized 13C pyruvate in vivo. Conclusion: This sequence forms an attractive method for acquiring hyperpolarized imaging datasets, providing adaptive spatiotemporal imaging to ameliorate the conflict of spatial and temporal resolution, with significant potential for clinical translation.

Read more
Medical Physics

A Beginner's Guide to Bloch Equation Simulations of Magnetic Resonance Imaging Sequences

Nuclear magnetic resonance (NMR) concepts are rooted in quantum mechanics, but MR imaging principles are well described and more easily grasped using classical ideas and formalisms such as Larmor precession and the phenomenological Bloch equations. Many textbooks provide in-depth descriptions and derivations of the various concepts. Still, carrying out numerical Bloch equation simulations of the signal evolution can oftentimes supplement and enrich one's understanding. And though it may appear intimidating at first, performing these simulations is within the realm of every imager. The primary objective herein is to provide novice MR users with the necessary and basic conceptual, algorithmic and computational tools to confidently write their own simulator. A brief background of the idealized MR imaging process, its concepts and the pulse sequence diagram are first provided. Thereafter, two regimes of Bloch equation simulations are presented, the first which has no radio frequency (RF) pulses, and the second in which RF pulses are applied. For the first regime, analytical solutions are given, whereas for the second regime, an overview of the computationally efficient, but often overlooked, Rodrigues' rotation formula is given. Lastly, various simulation conditions of interest and example code snippets are given and discussed to help demonstrate how straightforward and easy performing MR simulations can be.

Read more
Medical Physics

A Computer-Aided Diagnosis System Using Artificial Intelligence for Hip Fractures -Multi-Institutional Joint Development Research-

[Objective] To develop a Computer-aided diagnosis (CAD) system for plane frontal hip X-rays with a deep learning model trained on a large dataset collected at multiple centers. [Materials and Methods]. We included 5295 cases with neck fracture or trochanteric fracture who were diagnosed and treated by orthopedic surgeons using plane X-rays or computed tomography (CT) or magnetic resonance imaging (MRI) who visited each institution between April 2009 and March 2019 were enrolled. Cases in which both hips were not included in the photographing range, femoral shaft fractures, and periprosthetic fractures were excluded, and 5242 plane frontal pelvic X-rays obtained from 4,851 cases were used for machine learning. These images were divided into 5242 images including the fracture side and 5242 images without the fracture side, and a total of 10484 images were used for machine learning. A deep convolutional neural network approach was used for machine learning. Pytorch 1.3 and this http URL 1.0 were used as frameworks, and EfficientNet-B4, which is pre-trained ImageNet model, was used. In the final evaluation, accuracy, sensitivity, specificity, F-value and area under the curve (AUC) were evaluated. Gradient-weighted class activation mapping (Grad-CAM) was used to conceptualize the diagnostic basis of the CAD system. [Results] The diagnostic accuracy of the learning model was accuracy of 96. 1 %, sensitivity of 95.2 %, specificity of 96.9 %, F-value of 0.961, and AUC of 0.99. The cases who were correct for the diagnosis showed generally correct diagnostic basis using Grad-CAM. [Conclusions] The CAD system using deep learning model which we developed was able to diagnose hip fracture in the plane X-ray with the high accuracy, and it was possible to present the decision reason.

Read more
Medical Physics

A Critical Study of Cottenden et al.'s An Analytical Model of the Motion of a Conformable Sheet Over a General Convex Surface in the Presence of Frictional Coupling

In our analysis, we show that what Cottenden et al. accomplish is the derivation of the ordinary capstan equation, and a solution to a dynamic membrane with both a zero-Poisson's ratio and a zero-mass density on a rigid right-circular cone. The authors states that the capstan equation holds true for an elastic obstacle, and thus, it can be used to calculate the coefficient of friction between human skin and fabrics. However, using data that we gathered from human trials, we show that this claim cannot be substantiated as it is unwise to use the capstan equation (i.e. belt-friction models in general) to calculate the friction between in-vivo skin and fabrics. This is due to the fact that such models assume a rigid foundation, while human soft-tissue is deformable, and thus, a portion of the applied force to the fabric is expended on deforming the soft-tissue, which in turn leads to the illusion of a higher coefficient of friction when using belt-friction models.

Read more
Medical Physics

A DNA damage multi-scale model for NTCP in proton and hadron therapy

{\bf Purpose}: To develop a first principle and multi-scale model for normal tissue complication probability (NTCP) as a function of dose and LET for proton and in general for particle therapy with a goal of incorporating nano-scale radio-chemical to macro-scale cell biological pathways, spanning from initial DNA damage to tissue late effects. {\bf Methods}: The method is combination of analytical and multi-scale computational steps including (1) derivation of functional dependencies of NTCP on DNA driven cell lethality in nanometer and mapping to dose and LET in millimeter, and (2) 3D-surface fitting to Monte Carlo data set generated based on post radiation image change and gathered for a cohort of 14 pediatric patients treated by scanning beam of protons for ependymoma. We categorize voxel-based dose and LET associated with development of necrosis in NTCP. {\bf Result}: Our model fits well the clinical data, generated for post radiation tissue toxicity and necrosis. The fitting procedure results in extraction of in-{\it vivo} radio-biological α - β indices and their numerical values. {\bf Discussion and conclusion}: The NTCP model, explored in this work, allows to correlate the tissue toxicities to DNA initial damage, cell lethality and the properties and qualities of radiation, dose and LET.

Read more

Ready to get started?

Join us today