Advancements and Breakthroughs in Ultrasound Imaging

Ultrasonic imaging is a powerful diagnostic tool available to medical practitioners, engineers and researchers today. Due to the relative safety, and the non-invasive nature, ultrasonic imaging has become one of the most rapidly advancing technologies. These rapid advances are directly related to the parallel advancements in electronics, computing, and transducer technology together with sophisticated signal processing techniques. This book focuses on state of the art developments in ultrasonic imaging applications and underlying technologies presented by leading practitioners and researchers from many parts of the world

Real-Time Ultrasound Image-Guidance and Tracking in External Beam Radiotherapy

Background and Purpose - To evaluate the accuracy of Clarity (clinical version) system by using ultrasound phantom and some probe position. - To evaluate the intrafraction motion of prostate by collecting and analyzing ultrasound monitoring data from some patients. - To evaluate the accuracy of Clarity (Anticosti) system by using 3D phantom programmed with sinusoidal and breathing movement patterns to simulate computer-controlled based breath-hold phases interspersed with spontaneous breathing. - To evaluate the clinical applicability of Clarity (Anticosti) system for liver cases in healthy volunteers. The tracking results of healthy volunteers were compared to surface marker. - To evaluate the intrafraction motion during breath-hold in liver case by collecting and analyzing US monitoring data from some patients. Material and Methods The accuracy of Clarity (clinical version) system was evaluated using ultrasound phantom and some probe position. Two different probes were used: transabdominal ultrasound (TAUS) and transperineal ultrasound (TPUS) probe. Two positions of the phantom were used for TPUS, the vertical and the horizontal position. Intrafraction motion assessment of the prostate was based on continuous position monitoring with a 4D US system along the three directions; left(+)-right (LR), anterior(+)-posterior (AP), and inferior(+)-superior (SI). 770 US monitoring sessions in 38 prostate cancer patients’ normo-fractionated VMAT treatment series were retrospectively evaluated. The overall mean values and standard deviations (SD) along with random and systematic SDs were computed. The tracking accuracy of the research 4D US system was evaluated using two motion phantoms programmed with sinusoidal and breathing patterns to simulate free breathing and DIBH. The clinical performance was evaluated with 5 healthy volunteers. US datasets were acquired in computer-controlled DIBH with varying angular scanning angles. Tracked structures were renal pelvis (spherical structure) and portal/liver vein branches (non-spherical structure). An external marker was attached to the surface of both phantoms and volunteers as a secondary tracked object by an infrared camera for comparison. Residual intrafractional motion of DIBH tracking target relative to beginning position in each breath-hold plateau region was analysed along three directions; superior-inferior (SI), left-right (LR) and anterior-posterior (AP). 12 PTVs of 11 patients with primary/secondary liver tumours or adrenal gland/spleen metastases of diverse primaries were irradiated with SBRT in DIBH. Real time tracking of target or neighbouring surrogate structures was performed additionally using 4D US system during CBCT acquisition after permission of local IRB. Results The geometric positioning tolerance for Clarity-Sim and Clarity-Guide is 1 mm according to the manufacturer’s specifications. The results showed that all phantom and probe combinations met this criterion. The mean duration of each prostate monitoring session was 254s. The mean (μ), the systematic error () and the random error (σ) of intrafraction prostate motion were μ=(0.01, -0.08, 0.15)mm, =(0.30, 0.34, 0.23)mm and σ=(0.59, 0.73, 0.64)mm in LR, AP and SI direction, respectively. The percentage of treatments for which prostate motion was 2mm was present in about 0.67% of the data. The percentage increased to 2.42%, 6.14%, and 9.35% at 120s, 180s and 240s, respectively. The phantom measurements using Clarity (Anticosti) system showed increasing accuracy of US tracking with decreasing scanning range. The probability of lost tracking was higher for small scanning ranges (43.09% (10°) and 13.54% (20°)).The tracking success rates in healthy volunteers during DIBH were 93.24% and 89.86% for renal pelvis and portal vein branches, respectively. There was a strong correlation between the motion of the marker and the US tracking for the majority of analyzed breath-holds. 84.06% and 88.41% of renal pelvis target results and 82.26% and 91.94% of liver vein target results in AP and SI direction, the Pearson correlation coefficient was between 0.71 and 0.99. For evaluation of the intrafraction motion during breath-hold, 680 individual BHs during 93 treatment fractions were analysed. On visual control of tracking movies, target was lost in 27.9% of tracking, leaving a total of 490 BHs with optimal tracking. During these BHs, mean(+SD) target displacement were 1.7(+0.8)mm, 0.9(+0.4)mm, 2.2(+1.0)mm and 3.2(+1.0)mm for SI, LR, AP and 3D vector, respectively. Most of target displacement was below 2mm with percentage of 64.6%, 88.1% and 60.5% for SI, LR and AP, respectively. Data percentage of large target displacement increased with added BH time. At 5s, 3D vector of target displacement >10mm could be observed in 0.1% of data. Percentage values increased to 0.2%, 0.6%, and 1.1% at 10s, 15s and 20s, respectively. Conclusions The 4D US system offers a non-invasive method for online organ motion monitoring without additional ionizing radiation dose to the patient. The magnitudes of intrafraction prostate motion along the SI and AP directions were comparable. On average, the smallest motion was in the LR direction and the largest in AP direction. Most of the prostate displacements were within a few millimeters. However, with increased treatment time, larger 3D vector prostate displacements up to 18.30 mm could be observed. Shortening the treatment time can reduce the intrafractional motion and its effects and US monitoring can help to maximize treatment precision particularly in hypofractionated treatment regimens. For organ monitoring during BH application, the 4D US system showed a good performance and tracking accuracy in a 4D motion phantom when tracking a target that moves in accordance to a simulating breathing pattern. A 30°scanning range turned out to be an optimal parameter to track along with respiratory motion considering the accuracy of tracking and the possible loss of the tracked structure. The ultrasound tracking system is also applicable to a clinical setup with the tested hardware solution. The tracking capability of surrogate structures for upper abdominal lesions in DIBH is promising but needs further investigation in a larger cohort of patients. Ultrasound motion data show a strong correlation with surface motion data for most of individual breath-holds. Further improvement of the tracking algorithm is suggested to improve accuracy along with respiratory motion if using larger scanning angles for detection of high-amplitude motion and non-linear transformations of the tracking target. The exact quantification of residual motion impact requires an in-depth analysis of time spent at every position, nevertheless mean residual motion during DIBH is low and predominant direction is SI and AP. Only infrequently larger displacements of 3D vector >1 cm were observed, for short periods. Beam interruption at predefined thresholds could take DIBH treatments close to perfection. Key words: Medical Physics, 4D ultrasound, IGRT (image-guided radiotherapy), prostate motion, stereotactic body radiotherapy (SBRT), deep inspiratory breath-hold (DIBH)

Improving Radiotherapy Targeting for Cancer Treatment Through Space and Time

Radiotherapy is a common medical treatment in which lethal doses of ionizing radiation are preferentially delivered to cancerous tumors. In external beam radiotherapy, radiation is delivered by a remote source which sits several feet from the patient\u27s surface. Although great effort is taken in properly aligning the target to the path of the radiation beam, positional uncertainties and other errors can compromise targeting accuracy. Such errors can lead to a failure in treating the target, and inflict significant toxicity to healthy tissues which are inadvertently exposed high radiation doses. Tracking the movement of targeted anatomy between and during treatment fractions provides valuable localization information that allows for the reduction of these positional uncertainties. Inter- and intra-fraction anatomical localization data not only allows for more accurate treatment setup, but also potentially allows for 1) retrospective treatment evaluation, 2) margin reduction and modification of the dose distribution to accommodate daily anatomical changes (called `adaptive radiotherapy\u27), and 3) targeting interventions during treatment (for example, suspending radiation delivery while the target it outside the path of the beam). The research presented here investigates the use of inter- and intra-fraction localization technologies to improve radiotherapy to targets through enhanced spatial and temporal accuracy. These technologies provide significant advancements in cancer treatment compared to standard clinical technologies. Furthermore, work is presented for the use of localization data acquired from these technologies in adaptive treatment planning, an investigational technique in which the distribution of planned dose is modified during the course of treatment based on biological and/or geometrical changes of the patient\u27s anatomy. The focus of this research is directed at abdominal sites, which has historically been central to the problem of motion management in radiation therapy

4D offline PET-based treatment verification in ion beam therapy

Due to the accessible sharp dose gradients, external beam radiotherapy with protons and heavier ions enables a highly conformal adaptation of the delivered dose to arbitrarily shaped tumour volumes. However, this high conformity is accompanied by an increased sensitivity to potential uncertainties, e.g., due to changes in the patient anatomy. Additional challenges are imposed by respiratory motion which does not only lead to rapid changes of the patient anatomy, but, in the cased of actively scanned ions beams, also to the formation of dose inhomogeneities. Therefore, it is highly desirable to verify the actual application of the treatment and to detect possible deviations with respect to the planned irradiation. At present, the only clinically implemented approach for a close-in-time verification of single treatment fractions is based on detecting the distribution of β+-emitter formed in nuclear fragmentation reactions during the irradiation by means of positron emission tomography (PET). For this purpose, a commercial PET/CT (computed tomography) scanner has been installed directly next to the treatment rooms at the Heidelberg Ion-Beam Therapy Center (HIT). Up to present, the application of this treatment verification technique is, however, still limited to static target volumes. This thesis aimed at investigating the feasibility and performance of PET-based treatment verification under consideration of organ motion. In experimental irradiation studies with moving phantoms, not only the practicability of PET-based treatment monitoring for moving targets, using a commercial PET/CT device, could be shown for the first time, but also the potential of this technique to detect motion-related deviations from the planned treatment with sub-millimetre accuracy. The first application to four exemplary hepato-cellular carcinoma patient cases under substantially more challenging clinical conditions indicated potential for improvement by taking organ motion into consideration, particularly for patients exhibiting motion amplitudes of above 1cm and a sufficiently large number of detected true coincidences during their post-irradiation PET scan. Despite the application of an optimised PET image reconstruction scheme, as retrieved from a dedicated phantom imaging study in the scope of this work, the small number of counts and the resulting high level of image noise were identified as a major limiting factor for the detection of motion-induced dose inhomogeneities within the patient. Moreover, the biological washout modelling of the irradiation-induced isotopes proved to be not sufficiently accurate and thereby impede a quantitative analysis of measured and simulated data under consideration of target motion. In future, improvements are particularly foreseen through dedicated noise-robust time-resolved (4D) image reconstruction algorithms, an improved tracking of the organ motion, e.g., by ultrasound (US) imaging, as implemented for the first time in 4D PET imaging in the scope of this work, as well as by patient-specific washout models

A Survey on Deep Learning in Medical Image Analysis

Deep learning algorithms, in particular convolutional networks, have rapidly become a methodology of choice for analyzing medical images. This paper reviews the major deep learning concepts pertinent to medical image analysis and summarizes over 300 contributions to the field, most of which appeared in the last year. We survey the use of deep learning for image classification, object detection, segmentation, registration, and other tasks and provide concise overviews of studies per application area. Open challenges and directions for future research are discussed.Comment: Revised survey includes expanded discussion section and reworked introductory section on common deep architectures. Added missed papers from before Feb 1st 201

Theoretical investigation of transgastric and intraductal approaches for ultrasound-based thermal therapy of the pancreas.

BackgroundThe goal of this study was to theoretically investigate the feasibility of intraductal and transgastric approaches to ultrasound-based thermal therapy of pancreatic tumors, and to evaluate possible treatment strategies.MethodsThis study considered ultrasound applicators with 1.2 mm outer diameter tubular transducers, which are inserted into the tissue to be treated by an endoscopic approach, either via insertion through the gastric wall (transgastric) or within the pancreatic duct lumen (intraductal). 8 patient-specific, 3D, transient, biothermal and acoustic finite element models were generated to model hyperthermia (n = 2) and ablation (n = 6), using sectored (210°-270°, n = 4) and 360° (n = 4) transducers for treatment of 3.3-17.0 cm3 tumors in the head (n = 5), body (n = 2), and tail (n = 1) of the pancreas. A parametric study was performed to determine appropriate treatment parameters as a function of tissue attenuation, blood perfusion rates, and distance to sensitive anatomy.ResultsParametric studies indicated that pancreatic tumors up to 2.5 or 2.7 cm diameter can be ablated within 10 min with the transgastric and intraductal approaches, respectively. Patient-specific simulations demonstrated that 67.1-83.3% of the volumes of four sample 3.3-11.4 cm3 tumors could be ablated within 3-10 min using transgastric or intraductal approaches. 55.3-60.0% of the volume of a large 17.0 cm3 tumor could be ablated using multiple applicator positions within 20-30 min with either transgastric or intraductal approaches. 89.9-94.7% of the volume of two 4.4-11.4 cm3 tumors could be treated with intraductal hyperthermia. Sectored applicators are effective in directing acoustic output away from and preserving sensitive structures. When acoustic energy is directed towards sensitive structures, applicators should be placed at least 13.9-14.8 mm from major vessels like the aorta, 9.4-12.0 mm from other vessels, depending on the vessel size and flow rate, and 14 mm from the duodenum.ConclusionsThis study demonstrated the feasibility of generating shaped or conformal ablative or hyperthermic temperature distributions within pancreatic tumors using transgastric or intraductal ultrasound

First steps Toward Ultrasound-Based Motion compensation for imaging and Therapy: calibration with an Optical system and 4D PeT imaging

Target motion, particularly in the abdomen, due to respiration or patient movement is still a challenge in many diagnostic and therapeutic processes. Hence, methods to detect and compensate this motion are required. Diagnostic ultrasound (US) represents a non-invasive and dose-free alternative to fluoroscopy, providing more information about internal target motion than respiration belt or optical tracking. The goal of this project is to develop an US-based motion tracking for real-time motion correction in radiation therapy and diagnostic imaging, notably in 4D positron emission tomography (PET). In this work, a workflow is established to enable the transformation of US tracking data to the coordinates of the treatment delivery or imaging system - even if the US probe is moving due to respiration. It is shown that the US tracking signal is equally adequate for 4D PET image reconstruction as the clinically used respiration belt and provides additional opportunities in this concern. Furthermore, it is demonstrated that the US probe being within the PET field of view generally has no relevant influence on the image quality. The accuracy and precision of all the steps in the calibration workflow for US tracking-based 4D PET imaging are found to be in an acceptable range for clinical implementation. Eventually, we show in vitro that an US-based motion tracking in absolute room coordinates with a moving US transducer is feasible