Volumetric Imaging System Research Articles

Comparison of Different Registration Methods on Patient Set-Up Error During Volumetric Modulated Arc Therapy Using Cone-Beam CT Imaging for Lung Cancer

Background: The three-dimensional image-guided radiation therapy is very important in volumetric modulated arc therapy (VMAT) to enhance accuracy throughout the course of a patient's radiation treatment. The image guidance can ensure the safe administration of prescribed radiation dose to the patient. Aim: This study investigated patient set-up uncertainties based on three different registration methods in cone bean CT (CBCT) using volumetric modulated arc therapy (VMAT) for different clinical sites. Methods: A total of 396 CBCT performed for lung VMAT plan for patient set-up verification as per institution image guidance protocol. The approved CT images were transferred from treatment planning system (TPS) to x-ray volumetric imaging system (XVI) for reference image registration. The set-up errors in mediolateral (ML), craniocaudal (CC) and anterioposterior (AP) direction were determined using grayscale matching between the reference CT image and onboard CBCT images. For the current study, patient set-up verification was performed based on clip-box registration (CBR) for image matching. By considering clip-box registration as a reference, other two registration methods of mask registration (MR) and dual registration (DR) (clip-box and mask) were performed for comparison. To compare three registration methods, systematic error (∑), random error (σ), mean displacement, mean set-up error and maximum error were analyzed. Results: The systemic and random errors were less in clip-box registration as compared with other two registration ( P > 0.05). Similarly, maximum error, mean displacement error and mean set-up errors were observed less in clip-box registration as compared with mask and dual registration ( P > 0.05). However, statically no significant difference was observed between three different registration methods ( P > 0.05). Conclusion: All three registration methods can be used for patient set-up accuracy for lung VMAT plan. However, the current study suggested that clip-box method will be more efficient as compared with mask and dual registration methods.

A 3D printed phantom for Image Quality Assessment in Cone-beam CT

Aim The number of cone-beam scanners in use within medical, therapeutic and dental practices is increasing. Quality assurance standards require the assessment of image quality. Current phantoms are not cost effective or practical. The aim of this work was to create a practical 3D printed phantom to address the quality assurance needs of cone beam units particularly in the dental field. 3D printing has the potential to provide adaptable, reproducible, low cost phantoms for use in the field where offline access to images can be difficult. Materials and methods A phantom was designed which adhered to the requirements as outlined by the Sedentexct Guidelines. The design was constructed using 3D printing software (Solidworks, USA) to include modules for uniformity, resolution, contrast, geometrical and Hounsfield unit accuracy. A number of models, materials and production techniques were evaluated. Results A portable robust nylon phantom was created using selective laser sintering. Chambers in the phantom allowed filling with materials for assessment of Hounsfield units. Metal implants allowed assessment of geometric accuracy and potential artefacts. The phantom met the requirements of Sedentexct testing guidelines. The phantom assessed a cone-beam dental CT (Planmeca, Finland), an angiographic CT (Artis Q, Siemens) and a conventional CT (Sensation open, Siemens. Conclusion 3D printed nylon phantoms can be used to assess image quality and performance in multiple types of volumetric imaging systems.

A comprehensive evaluation of angular range and separation on image quality, image registration, and imaging dose for cone beam computed tomography in radiotherapy

We aimed to comprehensively evaluate the quality, dose, and registration of cone beam computed tomography (CBCT) images acquired with different angular range (θ) and angular separation (Δθ). Elekta XVI volumetric imaging system was used in this study. CBCT images of a Catphan 503 phantom were reconstructed with projections that were acquired under 17 × 8 different combinations of θ (200° to 360°) and Δθ (0.27° to 3.24°). The evaluation indices were contrast-to-noise ratio (CNR), spatial resolution (modulation transfer function [MTF50%]), uniformity, and registration accuracy. The weighted computed tomography dose index (CTDIw) of CTDI Head dosimetry phantom was measured for estimating radiation exposure. CNR changed little from θ = 200° to 260°, but increased by ≈ 2.0 times from θ = 260° to 360°. CNR also increased by ≈ 2.5 times from Δθ = 2.16° to 0.27°. MTF50% increased with Δθ being decreased, but had no dependence on θ. Image uniformity became better when θ was smaller or larger than 260°, but there was no correlation with Δθ. Registration of the overall body had a maximum error of 0.3 mm. The error of low-contrast objects' registration could reach as much as 1.3 mm. CTDIw showed a linear dependence on θ and 1/Δθ. Although the imaging dose is reduced with θ being decreased or Δθ being increased, the image quality may be degraded. Accuracy of image registration of a rigid body can be achieved; however, low-contrast objects' registration using images with inferior quality will introduce unacceptable errors for clinical use. Further, the benefits and extra dose received by the patients should be balanced, and scan protocols with θ between 210° and 260° or Δθ smaller than 0.54° should not be recommended.

Developing and validating a multivariable prediction model to improve the diagnostic accuracy in determination of cervical versus endometrial origin of uterine adenocarcinomas: A prospective MR study combining diffusion-weighted imaging and spectroscopy.

A triage test to assist clinical decision-making on choosing primary chemoradiation for cervical carcinomas or primary surgery for endometrial carcinomas is important. To develop and validate a multiparametric prediction model based on MR imaging and spectroscopy in distinguishing adenocarcinomas of uterine cervical or endometrial origin. Prospective diagnostic accuracy study. Eighty-seven women: 25 cervical and 62 endometrial adenocarcinomas divided into training (n = 43; cervical/endometrial adenocarcinomas = 11/32) and validation (n = 44; 14/30) datasets. The 3T diffusion-weighted (DW) MR imaging and MR spectroscopy. Morphology, volumetric DW MR imaging and spectroscopy (MDS) scoring system with total points 0-5, based on presence of the following MR features assessed independently by two radiologists: (a) epicenter at the cervix, (b) rim enhancement, (c) disrupted cervical stromal integrity, (d) mean volumetric apparent diffusion coefficient values (ADCmean) higher than 0.98 × 10-3 mm2 /s, (e) fatty acyl δ 1.3 ppm more than 161.92 mM. Histopathology as gold standard. Logistic regression and receiver operator characteristic (ROC) curves analysis. For both the training and validation datasets, the MDS score achieved an accuracy of 93.0% and 84.1%, significantly higher than that of morphology (88.4% and 79.5%), ADC value (74.4% and 68.2%), and spectroscopy (81.4% and 68.2%; P < 0.05 for all). The performances of the scoring were superior to the morphology in the training dataset (areas under the receiver operating characteristics curve [AUC] = 0.95 vs. 0.89; P = 0.046), but not in the validation dataset (AUC = 0.90 vs. 0.85; P = 0.289). MDS score has potentials to improve distinguishing adenocarcinomas of cervical or endometrial origin, and warrants large-scale studies for further validation. 1 Technical Efficacy: Stage 3 J. Magn. Reson. Imaging 2018;47:1654-1666.

Efficient 3-D Model-Based Reconstruction Scheme for Arbitrary Optoacoustic Acquisition Geometries.

Optimal optoacoustic tomographic sampling is often hindered by the frequency-dependent directivity of ultrasound sensors, which can only be accounted for with an accurate 3-D model. Herein, we introduce a 3-D model-based reconstruction method applicable to optoacoustic imaging systems employing detection elements with arbitrary size and shape. The computational complexity and memory requirements are mitigated by introducing an efficient graphic processing unit (GPU)-based implementation of the iterative inversion. On-the-fly calculation of the entries of the model-matrix via a small look-up table avoids otherwise unfeasible storage of matrices typically occupying more than 300GB of memory. Superior imaging performance of the suggested method with respect to standard optoacoustic image reconstruction methods is first validated quantitatively using tissue-mimicking phantoms. Significant improvements in the spatial resolution, contrast to noise ratio and overall 3-D image quality are also reported in real tissues by imaging the finger of a healthy volunteer with a hand-held volumetric optoacoustic imaging system.

Dual-energy imaging method to improve the image quality and the accuracy of dose calculation for cone-beam computed tomography

PurposeTo improve the image quality and accuracy of dose calculation for cone-beam computed tomography (CT) images through implementation of a dual-energy cone-beam computed tomography method (DE-CBCT), and evaluate the improvement quantitatively. MethodsTwo sets of CBCT projections were acquired using the X-ray volumetric imaging (XVI) system on a Synergy (Elekta, Stockholm, Sweden) system with 120kV (high) and 70kV (low) X-rays, respectively. Then, the electron density relative to water (relative electron density (RED)) of each voxel was calculated using a projection-based dual-energy decomposition method. As a comparison, single-energy cone-beam computed tomography (SE-CBCT) was used to calculate RED with the Hounsfield unit–RED calibration curve generated by a CIRS phantom scan with identical imaging parameters. The imaging dose was measured with a dosimetry phantom. The image quality was evaluated quantitatively using a Catphan 503 phantom with the evaluation indices of the reproducibility of the RED values, high-contrast resolution (MTF50%), uniformity, and signal-to-noise ratio (SNR). Dose calculation of two simulated volumetric-modulated arc therapy plans using an Eclipse treatment-planning system (Varian Medical Systems, Palo Alto, CA, USA) was performed on an Alderson Rando Head and Neck (H&N) phantom and a Pelvis phantom. Fan-beam planning CT images for the H&N and Pelvis phantom were set as the reference. A global three-dimensional gamma analysis was used to compare dose distributions with the reference. The average gamma values for targets and OAR were analyzed with paired t-tests between DE-CBCT and SE-CBCT. ResultsIn two scans (H&N scan and body scan), the imaging dose of DE-CBCT increased by 1.0% and decreased by 1.3%. It had a better reproducibility of the RED values (mean bias: 0.03 and 0.07) compared with SE-CBCT (mean bias: 0.13 and 0.16). It also improved the image uniformity (57.5% and 30.1%) and SNR (9.7% and 2.3%), but did not affect the MTF50%. Gamma analyses of the 3D dose distribution with criteria of 1%/1mm showed a pass rate of 99.0–100% and 85.3–97.6% for DE-CBCT and 73.5–99.1% and 80.4–92.7% for SE-CBCT. The average gamma values were reduced significantly by DE-CBCT (p< 0.05). Gamma index maps showed that matching of the dose distribution between CBCT-based and reference was improved by DE-CBCT. ConclusionsDE-CBCT can achieve both better image quality and higher accuracy of dose calculation, and could be applied to adaptive radiotherapy.

High-speed 3D imaging based on structured illumination and electrically tunable lens

In this Letter, we present a high-speed volumetric imaging system based on structured illumination and an electrically tunable lens (ETL), where the ETL performs fast axial scanning at hundreds of Hz. In the system, a digital micro-mirror device (DMD) is utilized to rapidly generate structured images at the focal plane in synchronization with the axial scanning unit. The scanning characteristics of the ETL are investigated theoretically and experimentally. Imaging experiments on pollen samples are performed to verify the optical cross-sectioning and fast axial scanning capabilities. The results show that our system can perform fast axial scanning and three-dimensional (3D) imaging when paired with a high-speed camera, presenting an economic solution for advanced biological imaging applications.

Motion quantification during multi-photon functional imaging in behaving animals.

Functional imaging in behaving animals is essential to understanding brain function. However, artifacts resulting from animal motion, including locomotion, can severely corrupt functional measurements. To dampen tissue motion, we designed a new optical window with minimal optical aberrations. Using the newly developed high-speed continuous volumetric imaging system based on an optical phase-locked ultrasound lens, we quantified motion of the cerebral cortex and hippocampal surface during two-photon functional imaging in behaving mice. We find that the out-of-plane motion is generally greater than the axial dimension of the point-spread-function during mouse locomotion, which indicates that high-speed continuous volumetric imaging is necessary to minimize motion artifacts.

SU‐F‐J‐47: Inherent Uncertainty in the Positional Shifts Determined by a Volumetric Cone Beam Imaging System

Purpose:To quantify inherent uncertainty associated with a volumetric imaging system in its determination of positional shifts.Methods:The study was performed on an Elekta Axesse™ linac's XVI cone beam computed tomography (CBCT) system. A CT image data set of a Penta‐ Guide phantom was used as reference image by placing isocenter at the center of the phantom.The phantom was placed arbitrarily on the couch close to isocenter and CBCT images were obtained. The CBCT dataset was matched with the reference image using XVI software and the shifts were determined in 6‐dimensions. Without moving the phantom, this process was repeated 20 times consecutively within 30 minutes on a single day. Mean shifts and their standard deviations in all 6‐dimensions were determined for all the 20 instances of imaging. For any given day, the first set of shifts obtained was kept as reference and the deviations of the subsequent 19 sets from the reference set were scored. Mean differences and their standard deviations were determined. In this way, data were obtained for 30 consecutive working days.Results:Tabulating the mean deviations and their standard deviations observed on each day for the 30 measurement days, systematic and random errors in the determination of shifts by XVI software were calculated. The systematic errors were found to be 0.03, 0.04 and 0.03 mm while random errors were 0.05, 0.06 and 0.06 mm in lateral, craniocaudal and anterio‐posterior directions respectively. For rotational shifts, the systematic errors were 0.02°, 0.03° and 0.03° and random errors were 0.06°, 0.05° and 0.05° in pitch, roll and yaw directions respectively.Conclusion:The inherent uncertainties in every image guidance system should be assessed and baseline values established at the time of its commissioning. These shall be periodically tested as part of the QA protocol.

SU‐F‐J‐126: Influence of Six Dimensional Motions in Frameless Stereotactic Dosimetry Incorporating Rotational Shifts as Equivalent Translational Shifts: A Feasibility Study for Elekta‐BrainLAB Stereotactic System

Purpose:Six dimensional positional shifts (translational and rotational) determined by a volumetric imaging system were mathematically combined and incorporated as simple translational shifts and the resultant impact on dose characteristics was studied.Methods:Thirty patients who underwent either single fraction (12 Gy) or five fractions (5 Gy per fraction) stereotactic treatments were included in this study. They were immobilized using a double layered thermoplastic mask from BrainLAB. Isocenter matching was done using infrared marker of ExacTrac. An initial cone beam CT (CBCT) gave positional shifts in 6‐dimensions that were applied through 6‐D motion enabled couch. A verification CBCT was done following corrections before treatment. These 6‐D positional shifts determined at each imaging session from the first CBCT were mathematically combined to give three simple translational shifts. Doses were recalculated in the patient matrix with these positional errors present by moving the whole image dataset. Doses were also recalculated after second CBCT with only residual errors present. PTV dose statistics were compared.Results:For the approved plans V100%(PTV), V100%(GTV), D95%(PTV), D95%(GTV), D1%(PTV) and D1%(GTV) were 96.2±3.0%, 98.2±1.4%, 102%±1.7%, 103±1.2%, 107.9±8.9% and 109.3±7.5% of prescription dose respectively. With the positional errors present (after 1st CBCT) the corresponding values were 86.7±4.9%, 91.3±2.9%, 89.6±4.2%, 95.9±3.7%, 108.3±9.9% and 108.6±4.5%. Post‐correction (after 2nd CBCT) with only residual errors present, values were 94.5±5.7%, 97.3±2.9%, 99.3%±3.2%, 102%±2.1%, 107.6±8.5% and 109.0±7.6% respectively. Significant and nominal OAR dose variation was observed between pre‐ and post‐table corrections.Conclusion:Positional errors significantly affect PTV dose statistics. They need to be corrected before delivery of stereotactic treatments although the magnitude of dose changes can vary from patient‐to‐patient depending on the tumor location. As expected after the table corrections, residual errors result in insignificant dose deviations. For frameless stereotactic treatments having a six‐dimensional motion enabled couch is highly recommended to reduce quantum of dose deviations.

3D reconstruction based on compressed-sensing (CS)-based framework by using a dental panoramic detector

In this work, we propose a practical method that can combine the two functionalities of dental panoramic and cone-beam CT (CBCT) features in one by using a single panoramic detector. We implemented a CS-based reconstruction algorithm for the proposed method and performed a systematic simulation to demonstrate its viability for 3D dental X-ray imaging. We successfully reconstructed volumetric images of considerably high accuracy by using a panoramic detector having an active area of 198.4 mm × 6.4 mm and evaluated the reconstruction quality as a function of the pitch (p) and the angle step (Δθ). Our simulation results indicate that the CS-based reconstruction almost completely recovered the phantom structures, as in CBCT, for p≤2.0 and θ≤6°, indicating that it seems very promising for accurate image reconstruction even for large-pitch and few-view data. We expect the proposed method to be applicable to developing a cost-effective, volumetric dental X-ray imaging system.

Radiothérapie adaptative en routine : point de vue de l’oncologue radiothérapeute

Adaptive radiotherapy is defined as all processes leading to the modification of a treatment plan on the basis of patient-specific variations observed during the course of a treatment. This concept is currently of particular relevance due to the development of onboard volumetric imaging systems, which allow for daily viewing of variations in both tumour and organs at risk in terms of position, shape or volume. However, its application in routine clinical practice is limited due to the demanding nature of the processes involved (re-delineation and replanning) and increased dependence on available human resources. Even if “online” strategies, based on deformable image registration (DIR) algorithms, could lead to a reduction in both work and calculation time, for the moment their use is limited to the research field due to uncertainties surrounding the validity of results gathered. Other strategies without DIR can be used as “offline” or “hybrid offline–online” strategies that seem to offer a compromise between time consumption and therapeutic gain for the patient.

Fish locomotion: recent advances and new directions.

Research on fish locomotion has expanded greatly in recent years as new approaches have been brought to bear on a classical field of study. Detailed analyses of patterns of body and fin motion and the effects of these movements on water flow patterns have helped scientists understand the causes and effects of hydrodynamic patterns produced by swimming fish. Recent developments include the study of the center-of-mass motion of swimming fish and the use of volumetric imaging systems that allow three-dimensional instantaneous snapshots of wake flow patterns. The large numbers of swimming fish in the oceans and the vorticity present in fin and body wakes support the hypothesis that fish contribute significantly to the mixing of ocean waters. New developments in fish robotics have enhanced understanding of the physical principles underlying aquatic propulsion and allowed intriguing biological features, such as the structure of shark skin, to be studied in detail.

Complementary coded apertures for 4-dimensional x-ray coherent scatter imaging.

X-ray scattering has played a key role in non-destructive materials characterization due to the material-specific coherent scattering signatures. In the current energy dispersive coherent scatter imaging systems, including selected volume tomography and coherent scatter computed tomography, each object voxel is measured at a single scatter angle, which suffers from slow acquisition time. The employment of coded apertures in x-ray scatter imaging systems improves the photon collection efficiency, making it promising for real time volumetric imaging and material identification. In this paper, we propose a volumetric x-ray scatter imaging system using a pair of complementary coded apertures: a coded aperture on the detector side introduces multiplexed measurement on an energy-sensitive detector array; a complementary source-side coded aperture selectively illuminates the object to decouple the ambiguity due to the increased parallelization for 4D imaging. The system yields the 1D coherent scattering form factor at each voxel in 3D. We demonstrate tomographic imaging and material identification with the system and achieve a spatial resolution ~1 cm and a normalized momentum transfer resolution, Δq/q, of 0.2.

A volumetric CMUT-based ultrasound imaging system simulator with integrated reception and μ-beamforming electronics models.

In modern ultrasound imaging devices, two-dimensional probes and electronic scanning allow volumetric imaging of anatomical structures. When dealing with the design of such complex 3-D ultrasound (US) systems, as the number of transducers and channels dramatically increases, new challenges concerning the integration of electronics and the implementation of smart micro-beamforming strategies arise. Hence, the possibility to predict the behavior of the whole system is mandatory. In this paper, we propose and describe an advanced simulation tool for ultrasound system modeling and simulation, which conjugates the US propagation and scattering, signal transduction, electronic signal conditioning, and beamforming in a single environment. In particular, we present the architecture and model of an existing 16-channel integrated receiver, which includes an amplification and micro-beamforming stage, and validate it by comparison with circuit simulations. The developed model is then used in conjunction with the transducer and US field models to perform a system simulation, aimed at estimating the performance of an example 3-D US imaging system that uses a capacitive micromachined ultrasonic transducer (CMUT) 2-D phased-array coupled to the modeled reception front-end. Results of point spread function (PSF) calculations, as well as synthetic imaging of a virtual phantom, show that this tool is actually able to model the complete US image reconstruction process, and that it could be used to quickly provide valuable system-level feedback for an optimized tuning of electronic design parameters.

A volumetric CMUT-based ultrasound imaging system simulator with integrated reception and μ-beamforming electronics models

A volumetric CMUT-based ultrasound imaging system simulator with integrated reception and μ-beamforming electronics models

Integrated Circuits for Volumetric Ultrasound Imaging With 2-D CMUT Arrays

Real-time volumetric ultrasound imaging systems require transmit and receive circuitry to generate ultrasound beams and process received echo signals. The complexity of building such a system is high due to requirement of the front-end electronics needing to be very close to the transducer. A large number of elements also need to be interfaced to the back-end system and image processing of a large dataset could affect the imaging volume rate. In this work, we present a 3-D imaging system using capacitive micromachined ultrasonic transducer (CMUT) technology that addresses many of the challenges in building such a system. We demonstrate two approaches in integrating the transducer and the front-end electronics. The transducer is a 5-MHz CMUT array with an 8 mm × 8 mm aperture size. The aperture consists of 1024 elements (32 × 32) with an element pitch of 250 μm. An integrated circuit (IC) consists of a transmit beamformer and receive circuitry to improve the noise performance of the overall system. The assembly was interfaced with an FPGA and a back-end system (comprising of a data acquisition system and PC). The FPGA provided the digital I/O signals for the IC and the back-end system was used to process the received RF echo data (from the IC) and reconstruct the volume image using a phased array imaging approach. Imaging experiments were performed using wire and spring targets, a ventricle model and a human prostrate. Real-time volumetric images were captured at 5 volumes per second and are presented in this paper.

Radiothérapie adaptative ORL

Onboard volumetric imaging systems can provide accurate data of the patient's anatomy during a course of head and neck radiotherapy making it possible to assess the actual delivered dose and to evaluate the dosimetric impact of complex daily positioning variations and gradual anatomic changes such as geometric variations of tumors and normal tissues or shrinkage of external contours. Adaptive radiotherapy is defined as the correction of a patient's treatment planning to adapt for individual variations observed during treatment. Strategies are developed to selectively identify patients that require replanning because of an intolerable dosimetric drift. Automated tools are designed to limit time consumption. Deformable image registration algorithms are the cornerstones of these strategies, but a better understanding of their limits of validity is required before adaptive radiotherapy can be safely introduced to daily practice. Moreover, strict evaluation of the clinical benefits is yet to be proven.

3-D airborne ultrasound synthetic aperture imaging based on capacitive micromachined ultrasonic transducers

In this paper, we present an airborne 3-D volumetric imaging system based on capacitive micromachined ultrasonic transducers (CMUTs). For this purpose we fabricated 89-kHz CMUTs where each CMUT is made of a circular single-crystal silicon plate with a radius of 1mm and a thickness of 20μm, which is actuated by electrostatic force through a 20-μm vacuum gap. The measured transmit sensitivity at 300-V DC bias is 14.6Pa/V and 24.2Pa/V, when excited by a 30-cycle burst and a continuous wave, respectively. The measured receive sensitivity at 300-V DC bias is 16.6mV/Pa (−35.6dB re 1V/Pa) for a 30-cycle burst. A 26×26 2-D array was implemented by mechanical scanning a co-located transmitter and receiver using the classic synthetic aperture (CSA) method. The measurement of a 1.6λ-size target at a distance of 500mm presented a lateral resolution of 3.17° and also showed good agreement with the theoretical point spread function. The 3-D imaging of two plates at a distance of 350mm and 400mm was constructed to exhibit the capability of the imaging system. This study experimentally demonstrates that a 2-D CMUT array can be used for practical 3-D imaging applications in air, such as a human–machine interface.

MO‐F‐217BCD‐01: Assessment of Image Quality in the New CT

The emergence of fully volumetric CT imaging systems and statistical / iterative reconstruction methods present an immediate need for rigorous methods of image quality assessment. Major themes arising in the widespread utilization of such technologies include: 1.) the reduction of radiation dose in a manner that maintains imaging performance with respect to the imaging task; 2.) the need for quantitative standards in image quality assessment appropriate to various vendor hardware and reconstruction systems; 3.) imaging performance metrics that provide meaningful descriptors of fully 3D spatial resolution and noise characteristics; 4.) the dependence of these metrics on acquisition technique, reconstruction parameters, and their applicability (or lack thereof) to novel reconstruction methods that may defy conventional metrics founded in assumptions of linearity and shift invariance; and 5.) methods for physical measurement (e.g., phantoms) and theoretical analysis of image quality for these new and emerging CT technologies and their implications for dose reduction.Learning Objectives:1. Understand the methods and metrics of image quality assessment for fully volumetric (cone‐beam) CT imaging using 3D filtered backprojection, including analysis of the 3D NPS, NEQ, and detectability index.2. Understand the limitations and assumptions of such metrics with respect to linearity, stationarity, and novel reconstruction techniques.3. Gain an understanding of how rigorous assessment of imaging performance can guide technique optimization, dose reduction, and the development of new CT technologies and applications.4. Understand the factors of image quality assessment in nonlinear statistical / model‐based 3D reconstruction techniques, including PSF and covariance estimation in nonstationary systems.5. Gain perspective on image quality assessment standards, including methods for dose and image quality measurement on different vendor platforms and the implications for dose reduction.