bluuebunny/crossref_metadata_2025 huggingface dataset:
MO‐E‐17A‐04: Size‐Specific Dose Estimate (SSDE) Provides a Simple Method to Calculate Organ Dose for Pediatric CT Examinations
Authors: Moore B , Brady S , Mirro A , Kaufman R
Published: July 2014

Purpose:

Investigate the correlation of SSDE with organ dose in a pediatric population.

Methods:

Four anthropomorphic phantoms, representing a range of pediatric body habitus, were scanned with MOSFET dosimeters placed at 23 organ locations to determine absolute organ dosimetry. Phantom organ dosimetry was divided by phantom SSDE to determine correlation between organ dose and SSDE. Correlation factors were then multiplied by patient SSDE to estimate patient organ dose. Patient demographics consisted of 352 chest and 241 abdominopelvic CT examinations, 22 ± 15 kg (range 5−55 kg) mean weight, and 6 ± 5 years (range 4 mon to 23 years) mean age. Patient organ dose estimates were compared to published pediatric Monte Carlo study results.

Results:

Phantom effective diameters were matched with patient population effective diameters to within 4 cm. 23 organ correlation factors were determined in the chest and abdominopelvic region across nine pediatric weight subcategories. For organs fully covered by the scan volume, correlation in the chest (average 1.1; range 0.7−1.4) and abdominopelvic (average 0.9; range 0.7−1.3) was near unity. For organs that extended beyond the scan volume (i.e., skin, bone marrow, and bone surface), correlation was determined to be poor (average 0.3; range: 0.1−0.4) for both the chest and abdominopelvic regions, respectively. Pediatric organ dosimetry was compared to published values and was found to agree in the chest to better than an average of 5% (27.6/26.2) and in the abdominopelvic region to better than 2% (73.4/75.0).

Conclusion:

Average correlation of SSDE and organ dosimetry was found to be better than ± 10% for fully covered organs within the scan volume. This study provides a list of organ dose correlation factors for the chest and abdominopelvic regions, and describes a simple methodology to estimate individual pediatric patient organ dose based on patient SSDE.
MO‐E‐17A‐08: Attenuation‐Based Size Adjusted, Scanner‐Independent Organ Dose Estimates for Head CT Exams: TG 204 for Head CT
Authors: McMillan K , Bostani M , Zankl M , DeMarco J , Cagnon C , McNitt‐Gray M
Published: July 2014

Purpose:

AAPM Task Group 204 described size specific dose estimates (SSDE) for body scans. The purpose of this work is to use a similar approach to develop patient‐specific, scanner‐independent organ dose estimates for head CT exams using an attenuation‐based size metric.

Methods:

For eight patient models from the GSF family of voxelized phantoms, dose to brain and lens of the eye was estimated using Monte Carlo simulations of contiguous axial scans for 64‐slice MDCT scanners from four major manufacturers. Organ doses were normalized by scannerspecific 16 cm CTDIvol values and averaged across all scanners to obtain scanner‐independent CTDIvol‐to‐organ‐dose conversion coefficients for each patient model. Head size was measured at the first slice superior to the eyes; patient perimeter and effective diameter (ED) were measured directly from the GSF data. Because the GSF models use organ identification codes instead of Hounsfield units, water equivalent diameter (WED) was estimated indirectly. Using the image data from 42 patients ranging from 2 weeks old to adult, the perimeter, ED and WED size metrics were obtained and correlations between each metric were established. Applying these correlations to the GSF perimeter and ED measurements, WED was calculated for each model. The relationship between the various patient size metrics and CTDIvol‐to‐organ‐dose conversion coefficients was then described.

Results:

The analysis of patient images demonstrated the correlation between WED and ED across a wide range of patient sizes. When applied to the GSF patient models, an exponential relationship between CTDIvol‐to‐organ‐dose conversion coefficients and the WED size metric was observed with correlation coefficients of 0.93 and 0.77 for the brain and lens of the eye, respectively.

Conclusion:

Strong correlation exists between CTDIvol normalized brain dose and WED. For the lens of the eye, a lower correlation is observed, primarily due to surface dose variations.

Funding Support: Siemens‐UCLA Radiology Master Research Agreement; Disclosures – Michael McNitt‐Gray: Institutional Research Agreement, Siemens AG; Research Support, Siemens AG; Consultant, Flaherty Sensabaugh Bonasso PLLC; Consultant, Fulbright and Jaworski
MO‐E‐17A‐09: Has Cancer Risk for Pediatric CT Increased Or Decreased? An Analysis of Cohort Data From 2004‐2013
Authors: Brady S , Kaufman R
Published: July 2014

Purpose:

To analyze CT radiation dosimetry trends in a pediatric population imaged with modern (2004‐2013) CT technology

Methods:

The institutional review board approved this retrospective review. Two cohorts of pediatric patients that received CT scans for treatment or surveillance for Wilms tumor (n=73) or Neuroblastoma (n=74) from 2004–2013 were included in this study. Patients were scanned during this time period on a GE Ultra (8 slice; 2004–2007), a GE VCT (2008–2011), or a GE VCT‐XTe (2011–2013). Each patient's individual or combined chest, abdomen, and pelvic CT exams (n=4138) were loaded onto a PACS workstation (Intelerad, Canada) and measured to calculate their effective diameter and SSDE. Patient SSDE was used to estimate patient organ dosimetry based on previously published data. Patient's organ dosimetry were sorted by gender, weight, age, scan protocol (i.e., chest, abdomen, or pelvis), and CT scanner technology and averaged accordingly to calculate population averaged absolute and effective dose values.

Results:

Patient radiation dose burden calculated for all genders, weights, and ages decreased at a rate of 0.2 mSv/year (4.2 mGy/year; average organ dose) from 2004–2013; overall levels decreased by 50% from 3.0 mSv (60.0 mGy) to 1.5 mSv (25.9 mGy). Patient dose decreased at equal rates for both male and female, and for individual scan protocols. The greatest dose savings was found for patients between 0–4 years old (65%) followed by 5‐9 years old (45%), 10–14 years old (30%), and > 14 years old (21%).

Conclusion:

Assuming a linear‐nothreshold model, there always will be potential risk of cancer induction from CT. However, as demonstrated among these patient populations, effective and organ dose has decreased over the last decade; thus, potential risk of long‐term side effects from pediatric CT examinations has also been reduced.
MO‐E‐17A‐10: Evaluation of Body and Head Dimensions of Pediatric Patients as a Function of Age
Authors: Seibert JA , Boone JM
Published: July 2014

Purpose:

Phantom development in medical physics plays an important role in radiation dose assessment and image quality evaluation, and this is especially true in the pediatric patient population. The purpose of this investigation was to establish the relationship between patient age and patient size, focusing on the abdomen‐pelvis and head effective diameters, for patients ranging in age from newborn to 18 years.

Methods:

A dose reporting tool for computed tomography systems was installed at our institution to achieve compliance with state law commencing on July 1, 2012. The software records a number of patient‐specific data, and also reports CT dose metrics (CTDIvol and DLP) into the patients interpretive report. The database generated by the software was mined to determine patient effective diameter as a function of age for pediatric patients aged 0–18 years. CT protocols including abdomen‐pelvis and routine head were evaluated, and specific to this study the patients age, gender and equivalent diameter were recorded.

Results:

Six age ranges were evaluated: A(0–3), B(4–6), C(7–9), D(10–12),E(13–15),F(16–18). For the torso in these groups based upon 694 patients, median effective diameters were 147, 167, 184, 214, 231, 246 mm, respectively. For the head (N=1833), median diameters were 143, 157, 162, 168, 174, and 174, respectively.

Conclusion:

A solid understanding of the approximate dimensions of pediatric patients as a function of age is useful in the development of age‐based imaging protocols and dose assessments. CT dose‐reporting tools generate a great deal of data with respect to body dimensions automatically. In this study, median equivalent diameters for the abdomen‐pelvis and head of pediatric patients were evaluated. These data may prove useful in the development of both mathematical and physical phantoms for dosimetry and image quality assessment.
MO‐F‐16A‐02: Simulation of a Medical Linear Accelerator for Teaching Purposes
Authors: Carlone M , Lamey M , Anderson R , MacPherson M
Published: July 2014

Purpose:

Detailed functioning of linear accelerator physics is well known. Less well developed is the basic understanding of how the adjustment of the linear accelerator's electrical components affects the resulting radiation beam. Other than the text by Karzmark, there is very little literature devoted to the practical understanding of linear accelerator functionality targeted at the radiotherapy clinic level. The purpose of this work is to describe a simulation environment for medical linear accelerators with the purpose of teaching linear accelerator physics.

Methods:

Varian type lineacs were simulated. Klystron saturation and peak output were modelled analytically. The energy gain of an electron beam was modelled using load line expressions. The bending magnet was assumed to be a perfect solenoid whose pass through energy varied linearly with solenoid current. The dose rate calculated at depth in water was assumed to be a simple function of the target's beam current. The flattening filter was modelled as an attenuator with conical shape, and the time‐averaged dose rate at a depth in water was determined by calculating kerma.

Results:

Fifteen analytical models were combined into a single model called SIMAC. Performance was verified systematically by adjusting typical linac control parameters. Increasing klystron pulse voltage increased dose rate to a peak, which then decreased as the beam energy was further increased due to the fixed pass through energy of the bending magnet. Increasing accelerator beam current leads to a higher dose per pulse. However, the energy of the electron beam decreases due to beam loading and so the dose rate eventually maximizes and the decreases as beam current was further increased.

Conclusion:

SIMAC can realistically simulate the functionality of a linear accelerator. It is expected to have value as a teaching tool for both medical physicists and linear accelerator service personnel.
MO‐F‐16A‐03: AAPM Online Learning Support of New ABR MOC Requirements
Authors: Bloch C , Ogburn J , Woodward M
Published: July 2014

In 2002 the American Board of Radiology (ABR) discontinued issuing lifetime board certification. After that time diplomates received a timelimited certificate and must participate in the Maintenance of Certification (MOC) program in order to maintain their certification. Initially certificates were issued with a 10 year expiration period and the MOC had requirements to be met over that 10 year period. The goal was to demonstrate continuous maintenance of clinical competency, however some diplomates were attempting to fulfill most or all of the requirements near the end of the 10 year period. This failed to meet the continuous aspect of the goal and so the ABR changed to a sliding 3‐year window. This was done to recognize that not every year would be the same, but that diplomates should be able to maintain a reasonable average over any 3 year period.A second significant change occurred in 2013. The initial requirements included 20 selfassessment modules (SAMs) over the original 10 year term. SAMs are a special type of continuing education (CE) credit that were an addition to the 250 standard CE credits required over the 10 year period. In 2013, however, the new requirement is 75 CE credits over the previous 3 years, of which 25 must include self‐assessment. Effectively this raised the self‐assessment requirement from 20 in 10 years to 25 in 3 years. Previously SAMs were an interactive presentation available in limited quantities at live meetings. However, the new requirement is not for SAMs but CE‐SA which includes SAMs, but also includes the online quizzes provided at the AAPM online learning center. All credits earned at the AAPM online learning center fulfill the ABR SA requirement. This talk will be an interactive demonstration of the AAPM online learning center along with a discussion of the MOC requirements.
MO‐F‐16A‐08: Have An Impact On More Patients From Your Ideas And Inventions
Authors: Morton R
Published: July 2014

Purpose:

To inform physicists how to obtain an FDA 510(k) clearance for the innovations they use in their facility and to make those ideas widely available to patients throughout the U.S.

Methods:

Give advice from 20 years experience of assisting in well over 100 successful 510(k) clearances.

Results:

Learn how to develop a 510(k) submission.

Conclusion:

Many physicists, physicians and radiation therapists have developed innovations that that are helpful to the patients in their institution. But, many of these innovations deserve to be made available to patients throughout the United States. The author, a Certified Radiological Physicist and former FDA employee, has consulted for over twenty years for inventors, start‐ups and established medical device manufacturers to bring new devices to market in the U.S. and to assist them to established FDA compliant quality systems for manufacturing. In this presentation the audience will learn the important points for deciding to go forward with obtaining a Premarket Notification clearance [also known as a 510(k) clearance] to legally market a medical device in the United States. The FDA has published guidelines for submitting a 510(k) application. However, the methods used to efficiently develop the documentation for submission and to obtain clearance in the shortest possible time comes from the author's experience in assisting well over one hundred successful 510(k) clearances.Whether you want to start your own company or to market your idea to an established medical device manufacturer, the value of your innovation increases with a documented 510(k) clearance from FDA.
MO‐PIS‐Exhibit Hall‐01: Tools for TG‐142 Linac Imaging QA I
Authors: Clements M , Wiesmeyer M
Published: July 2014

Partners in Solutions is an exciting new program in which AAPM partners with our vendors to present practical “hands‐on” information about the equipment and software systems that we use in our clinics. The therapy topic this year is solutions for TG‐142 recommendations for linear accelerator imaging QA. Note that the sessions are being held in a special purpose room built on the Exhibit Hall Floor, to encourage further interaction with the vendors.

Automated Imaging QA for TG‐142 with RIT

Presentation Time: 2:45 – 3:15 PM

This presentation will discuss software tools for automated imaging QA and phantom analysis for TG‐142. All modalities used in radiation oncology will be discussed, including CBCT, planar kV imaging, planar MV imaging, and imaging and treatment coordinate coincidence. Vendor supplied phantoms as well as a variety of third‐party phantoms will be shown, along with appropriate analyses, proper phantom setup procedures and scanning settings, and a discussion of image quality metrics. Tools for process automation will be discussed which include: RIT Cognition (machine learning for phantom image identification), RIT Cerberus (automated file system monitoring and searching), and RunQueueC (batch processing of multiple images). In addition to phantom analysis, tools for statistical tracking, trending, and reporting will be discussed. This discussion will include an introduction to statistical process control, a valuable tool in analyzing data and determining appropriate tolerances.

An Introduction to TG‐142 Imaging QA Using Standard Imaging Products

Presentation Time: 3:15 – 3:45 PM

Medical Physicists want to understand the logic behind TG‐142 Imaging QA. What is often missing is a firm understanding of the connections between the EPID and OBI phantom imaging, the software “algorithms” that calculate the QA metrics, the establishment of baselines, and the analysis and interpretation of the results. The goal of our brief presentation will be to establish and solidify these connections.

Our talk will be motivated by the Standard Imaging, Inc. phantom and software solutions. We will present and explain each of the image quality metrics in TG‐142 in terms of the theory, mathematics, and algorithms used to implement them in the Standard Imaging PIPSpro software. In the process, we will identify the regions of phantom images that are analyzed by each algorithm. We then will discuss the process of the creation of baselines and typical ranges of acceptable values for each imaging quality metric.
MO‐G‐18A‐01: Radiation Dose Reducing Strategies in CT, Fluoroscopy and Radiography
Authors: Mahesh M , Gingold E , Jones A
Published: July 2014

Advances in medical x‐ray imaging have provided significant benefits to patient care.

According to NCRP 160, there are more than 400 million x‐ray procedures performed annually in the United States alone that contributes to nearly half of all the radiation exposure to the US population. Similar growth trends in medical x‐ray imaging are observed worldwide. Apparent increase in number of medical x‐ray imaging procedures, new protocols and the associated radiation dose and risk has drawn considerable attention. This has led to a number of technological innovations such as tube current modulation, iterative reconstruction algorithms, dose alerts, dose displays, flat panel digital detectors, high efficient digital detectors, storage phosphor radiography, variable filters, etc. that are enabling users to acquire medical x‐ray images at a much lower radiation dose. Along with these, there are number of radiation dose optimization strategies that users can adapt to effectively lower radiation dose in medical x‐ray procedures. The main objectives of this SAM course are to provide information and how to implement the various radiation dose optimization strategies in CT, Fluoroscopy and Radiography.

Learning Objectives:

To update impact of technological advances on dose optimization in medical imaging.

To identify radiation optimization strategies in computed tomography.

To describe strategies for configuring fluoroscopic equipment that yields optimal images at reasonable radiation dose.

To assess ways to configure digital radiography systems and recommend ways to improve image quality at optimal dose.
MO‐G‐BRE‐03: Automated Continuous Monitoring of Patient Setup with Second‐Check Independent Image Registration
Authors: Jiang X , Fox T , Schreibmann E
Published: July 2014

Purpose:

To create a non‐supervised quality assurance program to monitor image‐based patient setup. The system acts a secondary check by independently computing shifts and rotations and interfaces with Varian's database to verify therapist's work and warn against sub‐optimal setups.

Methods:

Temporary digitally‐reconstructed radiographs (DRRs) and OBI radiographic image files created by Varian's treatment console during patient setup are intercepted and used as input in an independent registration module customized for accuracy that determines the optimal rotations and shifts. To deal with the poor quality of OBI images, a histogram equalization of the live images to the DDR counterparts is performed as a pre‐processing step. A search for the most sensitive metric was performed by plotting search spaces subject to various translations and convergence analysis was applied to ensure the optimizer finds the global minima. Final system configuration uses the NCC metric with 150 histogram bins and a one plus one optimizer running for 2000 iterations with customized scales for translations and rotations in a multi‐stage optimization setup that first corrects and translations and subsequently rotations.

Results:

The system was installed clinically to monitor and provide almost real‐time feedback on patient positioning. On a 2 month‐basis uncorrected pitch values were of a mean 0.016° with standard deviation of 1.692°, and couch rotations of − 0.090°± 1.547°. The couch shifts were −0.157°±0.466° cm for the vertical, 0.045°±0.286 laterally and 0.084°± 0.501° longitudinally. Uncorrected pitch angles were the most common source of discrepancies. Large variations in the pitch angles were correlated with patient motion inside the mask.

Conclusion:

A system for automated quality assurance of therapist's registration was designed and tested in clinical practice. The approach complements the clinical software's automated registration in terms of algorithm configuration and performance and constitutes a practical approach to implement safe and cost‐effective radiotherapy.
MO‐G‐BRD‐01: Point/Counterpoint Debate: Arc Based Techniques Will Make Conventional IMRT Obsolete
Authors: Shepard D , Popple R , Balter P
Published: July 2014

A variety of intensity modulated radiation therapy (IMRT) delivery techniques have been developed that have provided clinicians with the ability to deliver highly conformal dose distributions. The delivery techniques include compensators, step‐and‐shoot IMRT, sliding window IMRT, volumetric modulated arc therapy (VMAT), and tomotherapy. A key development in the field of IMRT was the introduction of new planning algorithms and delivery control systems in 2007 that made it possible to coordinate the gantry rotation speed, dose rate, and multileaf collimator leaf positions during the delivery of arc therapy. With these developments, VMAT became a routine clinical tool. The use of VMAT has continued to grow in recent years and some would argue that this will soon make conventional IMRT obsolete, and this is the premise of this debate. To introduce the debate, David Shepard, Ph.D. will provide an overview of IMRT delivery techniques including historical context and how they are being used today. The debate will follow with Richard Popple, Ph.D. arguing FOR the Proposition and Peter Balter, Ph.D. arguing AGAINST it.

Learning Objectives:

Understand the different delivery techniques for IMRT.

Understand the potential benefits of conventional IMRT.

Understand the potential benefits of arc‐based IMRT delivery.
MO‐G‐BRF‐02: Enhancement of Texture‐Based Metastasis Prediction Models Via the Optimization of PET/MRI Acquisition Protocols
Authors: Vallieres M , Laberge S , R. Levesque I , El Naqa I
Published: July 2014

Purpose:

We have previously identified a prediction model of lung metastases at diagnosis of soft‐tissue sarcomas (STS) that is composed of two textural features extracted from FDG‐PET and T1‐weighted (T1w) MRI scans. The goal of this study is to evaluate whether the optimization in FDGPET and MRI acquisition parameters would enhance the prediction performance of texture‐based models.

Methods:

Ten FDG‐PET and T1w‐ MRI digitized tumor models were generated from imaging data of STS patients who underwent pre‐treatment clinical scans between 2005 and 2011. Five of ten patients eventually developed lung metastases. Numerically simulated MR images were produced using echo times (TE) of 2 and 4 times the nominal clinical parameter (TEc), and repetition times (TR) of 0.5, 0.67, 1.5 and 2 times the nominal clinical parameter (TRc) found in the DICOM headers (TEc range: 9–13 ms, TRc range: 410‐667 ms). PET 2D images were simulated using Monte‐Carlo and were reconstructed using an ordered‐subsets expectation maximization (OSEM) algorithm with 1 to 32 iterations and a post‐reconstruction Gaussian filter of 0, 2, 4 or 6 mm width. For all possible combinations of PET and MRI acquisition parameters, the prediction model was constructed using logistic regression with new coefficients, and its associated prediction performance for lung metastases was evaluated using the area under the ROC curve (AUC).

Results:

The prediction performance over all simulations yielded AUCs ranging from 0.7 to 1. Notably, TR values below or equal to TRc and higher PET post‐reconstruction filter widths yielded higher prediction performance. The best results were obtained with a combination of 4*TEc, TRc, 30 OSEM iterations and 2mm filter width.

Conclusion:

This work indicates that texture‐based metastasis prediction models could be improved using optimized choices of FDG‐PET and MRI acquisition protocols. This principle could be generalized to other texture‐based models.
MO‐G‐BRF‐05: Determining Response to Anti‐Angiogenic Therapies with Monte Carlo Tumor Modeling
Authors: Valentinuzzi D , Simoncic U , Titz B , Jeraj R
Published: July 2014

Purpose:

Patient response to anti‐angiogenic therapies with vascular endothelial growth factor receptor – tyrosine kinase inhibitors (VEGFR TKIs) is heterogeneous. This study investigates key biological characteristics that drive differences in patient response via Monte Carlo computational modeling capable of simulating tumor response to therapy with VEGFR TKI.

Methods:

VEGFR TKIs potently block receptors, responsible for promoting angiogenesis in tumors. The model incorporates drug pharmacokinetic and pharmacodynamic properties, as well as patientspecific data of cellular proliferation derived from [18F]FLT‐PET data. Sensitivity of tumor response was assessed for multiple parameters, including initial partial oxygen tension (pO2), cell cycle time, daily vascular growth fraction, and daily vascular regression fraction. Results were benchmarked to clinical data (patient 2 weeks on VEGFR TKI, followed by 1‐week drug holiday). The tumor pO2 was assumed to be uniform.

Results:

Among the investigated parameters, the simulated proliferation was most sensitive to the initial tumor pO2. Initial change of 5 mmHg can already Result in significantly different levels of proliferation. The model reveals that hypoxic tumors (pO2 ≥ 20 mmHg) show the highest decrease of proliferation, experiencing mean FLT standardized uptake value (SUVmean) decrease for at least 50% at the end of the clinical trial (day 21). Oxygenated tumors (pO2 20 mmHg) show a transient SUV decrease (30–50%) at the end of the treatment with VEGFR TKI (day 14) but experience a rapid SUV rebound close to the pre‐treatment SUV levels (70–110%) at the time of a drug holiday (day 14–21) – the phenomenon known as a proliferative flare.

Conclusion:

Model's high sensitivity to initial pO2 clearly emphasizes the need for experimental assessment of the pretreatment tumor hypoxia status, as it might be predictive of response to antiangiogenic therapies and the occurrence of proliferative flare. Experimental assessment of other model parameters would further improve understanding of patient response.
MO‐G‐17A‐05: PET Image Deblurring Using Adaptive Dictionary Learning
Authors: Valiollahzadeh S , Clark J , Mawlawi O
Published: July 2014

Purpose:

The aim of this work is to deblur PET images while suppressing Poisson noise effects using adaptive dictionary learning (DL) techniques.

Methods:

The model that relates a blurred and noisy PET image to the desired image is described as a linear transform y=Hm+n where m is the desired image, H is a blur kernel, n is Poisson noise and y is the blurred image. The approach we follow to recover m involves the sparse representation of y over a learned dictionary, since the image has lots of repeated patterns, edges, textures and smooth regions. The recovery is based on an optimization of a cost function having four major terms: adaptive dictionary learning term, sparsity term, regularization term, and MLEM Poisson noise estimation term. The optimization is solved by a variable splitting method that introduces additional variables. We simulated a 128×128 Hoffman brain PET image (baseline) with varying kernel types and sizes (Gaussian 9×9, σ=5.4mm; Uniform 5×5, σ=2.9mm) with additive Poisson noise (Blurred). Image recovery was performed once when the kernel type was included in the model optimization and once with the model blinded to kernel type. The recovered image was compared to the baseline as well as another recovery algorithm PIDSPLIT+ (Setzer et. al.) by calculating PSNR (Peak SNR) and normalized average differences in pixel intensities (NADPI) of line profiles across the images.

Results:

For known kernel types, the PSNR of the Gaussian (Uniform) was 28.73 (25.1) and 25.18 (23.4) for DL and PIDSPLIT+ respectively. For blinded deblurring the PSNRs were 25.32 and 22.86 for DL and PIDSPLIT+ respectively. NADPI between baseline and DL, and baseline and blurred for the Gaussian kernel was 2.5 and 10.8 respectively.

Conclusion:

PET image deblurring using dictionary learning seems to be a good approach to restore image resolution in presence of Poisson noise. GE Health Care
MO‐G‐17A‐07: Improved Image Quality in Brain F‐18 FDG PET Using Penalized‐Likelihood Image Reconstruction Via a Generalized Preconditioned Alternating Projection Algorithm: The First Patient Results
Authors: Schmidtlein CR , Li S , Wu Z , Zhang J , Vogelsang L , Shen L , Xu Y , Feiglin D , Beattie B , Humm J , Krol A
Published: July 2014

Purpose:

To investigate the performance of a new penalized‐likelihood PET image reconstruction algorithm using the 11‐norm total‐variation (TV) sum of the 1st through 4th‐order gradients as the penalty. Simulated and brain patient data sets were analyzed.

Methods:

This work represents an extension of the preconditioned alternating projection algorithm (PAPA) for emission‐computed tomography. In this new generalized algorithm (GPAPA), the penalty term is expanded to allow multiple components, in this case the sum of the 1st to 4th order gradients, to reduce artificial piece‐wise constant regions (“staircase” artifacts typical for TV) seen in PAPA images penalized with only the 1st order gradient. Simulated data were used to test for “staircase” artifacts and to optimize the penalty hyper‐parameter in the root‐mean‐squared error (RMSE) sense. Patient FDG brain scans were acquired on a GE D690 PET/CT (370 MBq at 1‐hour post‐injection for 10 minutes) in time‐of‐flight mode and in all cases were reconstructed using resolution recovery projectors. GPAPA images were compared PAPA and RMSE‐optimally filtered OSEM (fully converged) in simulations and to clinical OSEM reconstructions (3 iterations, 32 subsets) with 2.6 mm XYGaussian and standard 3‐point axial smoothing post‐filters.

Results:

The results from the simulated data show a significant reduction in the “staircase” artifact for GPAPA compared to PAPA and lower RMSE (up to 35%) compared to optimally filtered OSEM. A simple power‐law relationship between the RMSE‐optimal hyper‐parameters and the noise equivalent counts (NEC) per voxel is revealed. Qualitatively, the patient images appear much sharper and with less noise than standard clinical images. The convergence rate is similar to OSEM.

Conclusions:

GPAPA reconstructions using the 11‐norm total‐variation sum of the 1st through 4th‐order gradients as the penalty show great promise for the improvement of image quality over that currently achieved with clinical OSEM reconstructions.
MO‐G‐18C‐01: BEST IN PHYSICS (IMAGING) – Novel Correction of Signal Modulation and Motion Artifacts in Temporal Bone BSSFP MRI
Authors: Hoff M , Xiang Q , Wilson G , Andre J
Published: July 2014

Purpose:

Phase cycled balanced steady state free precession (bSSFP) magnetic resonance (MR) images demonstrate high contrast in the temporal bone region, but are limited by motion artifacts stemming from globe motion, CSF and carotid artery pulsation, and by signal loss/modulation typical of bSSFP imaging of complex tissue environments. We sought to generate images delineating the fine morphology of temporal bone structures while minimizing signal loss and motion artifacts.

Methods:

Four axial 3D bSSFP MR images with Δθ = 0°, 90°, 180°, and 270° phase cycling respectively were acquired with a Philips Ingenia 3T MRI scanner in 2.3 minutes of total scan time. Other parameters included a 30° flip angle applied with a transmit/receive radiofrequency head coil, TE/TR = 4.2/2.1ms, receiver bandwidth = 890 Hz/pixel, and 180/180/120 matrix size and 1/1/1 mm voxel size along frequency/phase/slice directions. Complex image data were input into the Geometric Solution (GS) algorithm for calculation of artifact‐free bSSFP signal on a pixel‐by‐pixel basis. SNR was improved by linearizing the solution in a second‐pass regional optimization.

Results:

The GS eliminated the bSSFP signal intensity modulations while minimizing motion artifacts present in the original four images. The efficacy of the GS is validated through comparison with a complex average of the four original bSSFP images; unlike the GS, the complex average only moderates artifacts.

Conclusion:

The GS represents a novel method of correcting bSSFP MRI signal modulation and motion artifacts while maintaining contrast near the temporal bone. The technique is fast, easy to implement, and requires minimal post‐processing. This technique may inspire early clinical adoption, as it overcomes two major artifactual obstacles which have historically limited the widespread use of bSSFP MRI.
MO‐G‐18C‐06: MRI QC: Effects of Multi‐Channel Coil Element Failure On Image Quality
Authors: Li G , Dodge C , Reeve D
Published: July 2014

Purpose:

To quantitatively evaluate changes in phantom quality control (QC) measurements resulting from malfunctioning channels in multichannel brain coils during routine MRI QC.

Methods:

The large ACR MRI phantom was scanned on a 1.5T GE HDXt scanner using an 8‐channel brain array and on a 1.5T Siemens Aera using a 20‐channel head‐neck array. For the 8‐channel array, images were acquired by sequentially turning off an increasing number of adjacent channels. For the 20‐channel array, images were acquired with various combinations of active coil elements. Percent integral uniformity (PIU), signal‐to‐noise ratio (SNR) and ghosting ratio were measured with and without uniformity correction (UC).

Results:

For the 8‐channel array, SNR and PIU decreased with the number of inactive coil elements (57% and 34%, respectively). UC increased PIU to >82% and SNR to 80%, but also increased apparent ghosting due to background nonuniformity. For the 20‐channel array, the central pair of element groups (H3‐H4) closest to the phantom had the greatest impact on image quality. Without UC, PIU and SNR were similar when all groups or both H3‐H4 were active. Without UC, PIU decreased by 50% when either H3 or H4 was deactivated. Noise greatly decreased resulting in a ∼500% increase in SNR. Without UC, SNR decreased by 60% and PIU increased when both H3‐H4 were deactivated. PIU was most affected by UC (50%–160% increase). For both coils, ghosting ratio generally increased with UC but not above ACR limit (2.5%). With UC applied, PIU failed the ACR limit (87.5%) when 2 elements of the 8‐channel array or H3‐H4 were inactive.

Conclusion:

Channel failure for the two multichannel arrays tested was reflected in changes in SNR and PIU. For daily MR QC, setting coil‐specific SNR, PIU and ghosting QC limits to ensure the detection of malfunctioning elements is necessary due to coil design variations.
MO‐G‐18C‐08: Increasing Throughput of a Clinical MR Protocol for Prostate Cancer with a Factor of Two Using Multiband Imaging
Authors: Stemkens B , Andreychenko A , Crijns S , Sbrizzi A , Lagendijk J , van den Berg C , Tijssen R
Published: July 2014

Purpose:

To increase throughput of a clinical, multi‐parametric, prostate MRI protocol by individual scan acceleration using multiband excitation, in which multiple slices are excited simultaneously, and CAIPIRINHA.

Methods:

A healthy subject was scanned on a 3T clinical MR‐system with a 16‐channel torso receive array. A T2w‐TSE scan from a clinical prostate MR protocol was acquired to simulate three acceleration Methods: (1) traditional in‐plane parallel imaging (SENSE) (R=2), (2) multi‐slice parallel imaging (MS‐SENSE, R=2), in which two slices are acquired simultaneously and (3) multi‐slice CAIPIRINHA (R=2), in which one of the simultaneously acquired slices is shifted with FOV/2 with respect to the other slice. The normalized expected SNR was calculated within an ROI in the center of the slice. To demonstrate the feasibility of multiband MRI for the prostate, two 2D gradient echo slices (TE/TR=2.4ms/5.0ms, FA=20°, FOV=250×405mm2, voxelsize=0.5×0.5×4mm3, slice gap=20mm) were excited simultaneously using a numerically designed multiband RF pulse. The slices were acquired either with or without shifting the second slice by FOV/2 (i.e. CAIPIRINHA).

Results:

Simulations showed an expected relative SNR of 0.67 for in‐plane two‐fold SENSE acceleration, 0.14 for multi‐slice SENSE, and 0.94 for multi‐slice CAIPIRINHA within the ROI (SNR=1 for non‐accelerated acquisition). In‐vivo multiband experiments demonstrated that separation of the simultaneously acquired slices was practically impossible when slices folded on top of each other. However, the multi‐slice CAIPIRINHA experiment, showed low g‐factors and good image quality after unfolding.

Conclusion:

We demonstrated that the twofold multiband acceleration with CAIPIRINHA technique is the most SNR beneficial compared to the other acceleration techniques with only a moderate SNR penalty compared to the non‐accelerated acquisition. In‐vivo experiments demonstrated the feasibility of two‐fold CAIPIRINHA acceleration for pelvic MRI. This can be used to e.g. increase patient throughput, SNR or temporal resolution of the scans included in the multiparametric prostate MR protocol.
MO‐G‐12A‐01: Quantitative Imaging Metrology: What Should Be Assessed and How?
Authors: Giger M , Petrick N , Obuchowski N , Kinahan P
Published: July 2014

The first two symposia in the Quantitative Imaging Track focused on 1) the introduction of quantitative imaging (QI) challenges and opportunities, and QI efforts of agencies and organizations such as the RSNA, NCI, FDA, and NIST, and 2) the techniques, applications, and challenges of QI, with specific examples from CT, PET/CT, and MR. This third symposium in the QI Track will focus on metrology and its importance in successfully advancing the QI field. While the specific focus will be on QI, many of the concepts presented are more broadly applicable to many areas of medical physics research and applications. As such, the topics discussed should be of interest to medical physicists involved in imaging as well as therapy. The first talk of the session will focus on the introduction to metrology and why it is critically important in QI. The second talk will focus on appropriate methods for technical performance assessment. The third talk will address statistically valid methods for algorithm comparison, a common problem not only in QI but also in other areas of medical physics. The final talk in the session will address strategies for publication of results that will allow statistically valid meta‐analyses, which is critical for combining results of individual studies with typically small sample sizes in a manner that can best inform decisions and advance the field.

Learning Objectives:

Understand the importance of metrology in the QI efforts.

Understand appropriate methods for technical performance assessment.

Understand methods for comparing algorithms with or without reference data (i.e., “ground truth”).

Understand the challenges and importance of reporting results in a manner that allows for statistically valid meta‐analyses.
MO‐H‐19A‐01: FEATURED PRESENTATION – Treatment Planning Tool for Radiotherapy with Very High‐Energy Electron Beams
Authors: Bazalova M , Qu B , Hynning E , Hardemark B , Palma B , Loo B , Maxim P
Published: July 2014

Purpose:

To develop a tool for treatment planning optimization for fast radiotherapy delivered with very high‐energy electron beams (VHEE) and to compare VHEE plans to state‐of‐the‐art plans for challenging pelvis and H' N cases.

Methods:

Treatment planning for radiotherapy delivered with VHEE scanning pencil beams was performed by integrating EGSnrc Monte Carlo (MC) dose calculations with spot scanning optimization run in a research version of RayStation. A Matlab GUI for MC beamlet generation was developed, in which treatment parameters such as the pencil beam size and spacing, energy and number of beams can be selected. Treatment planning study for H' N and pelvis cases was performed and the effect of treatment parameters on the delivered dose distributions was evaluated and compared to the clinical treatment plans. The pelvis case with a 691cm3 PTV was treated with 2‐arc 15MV VMAT and the H' N case with four PTVs with total volume of 531cm3 was treated with 4‐arc 6MV VMAT.

Results:

Most studied VHEE plans outperformed VMAT plans. The best pelvis 80MeV VHEE plan with 25 beams resulted in 12% body dose sparing and 8% sparing to the bowel and right femur compared to the VMAT plan. The 100MeV plan was superior to the 150MeV plan. Mixing 100 and 150MeV improved dose sparing to the bladder by 7% compared to either plan. Plans with 16 and 36 beams did not significantly affect the dose distributions compared to 25 beam plans. The best H' N 100MeV VHEE plan decreased mean doses to the brainstem, chiasm, and both globes by 10‐42% compared to the VMAT plan.

Conclusion:

The pelvis and H' N cases suggested that sixteen 100MeV beams might be sufficient specifications of a novel VHEE treatment machine. However, optimum machine parameters will be determined with the presented VHEE treatment‐planning tool for a large number of clinical cases.

BW Loo and P Maxim received research support from RaySearch Laboratories. E Hynning and B Hardemark are employees of RaySearch Laboratories.
MO‐H‐19A‐02: Investigation of Modulated Electron Arc (MeArc) Therapy for the Treatment of Scalp Tumors
Authors: Eldib A , Jin L , Martin J , Li J , Chibani O , Galloway T , Ma C
Published: July 2014

Purpose:

Electron arc therapy has long been proposed as the most suitable technique for the treatment of superficial tumors that follow circularly curved surfaces. However it was challenged by unsuitability of the conventional applicators and the lack of adequate 3‐D dose calculation tools for arc electron beams in the treatment planning systems (TPS). Now with the availability of an electron specific multi‐leaf collimator (eMLC) and an in‐house Monte Carlo (MC) based TPS, we were motivated to investigate more advanced modulated electron arc (MeARC) therapy and its beneficial outcome.

Methods:

We initiated the study by a film measurement conducted in a head and neck phantom, where we delivered electron arcs in a step and shoot manner using the light field as a guide to avoid fields abutments. This step was done to insure enough clearance for the arcs with eMLC. MCBEAM and MCPLAN MC codes were used for the treatment head simulation and phantom dose calculation, respectively. Treatment plans were generated for targets drawn in real patient CTs and head and neck phantom. We utilized beams eye view available from a commercial planning system to create beamlets having same isocenter and adjoined at the scalp surface. Then dose‐deposition coefficients from those beamlets were calculated for all electron energies using MCPLAN. An in‐house optimization code was then used to find the optimum weights needed from individual beamlets.

Results:

MeARC showed a nicely tailored dose distribution around the circular curved target on the scalp. Some hot spots were noticed and could be attributed to fields abutment problem owing to the bulging nature of electron profiles. Brain dose was shown to be at lower levels compared to photon treatment.

Conclusion:

MeARC was shown to be a promising modality for treating scalp cases and could be beneficial to all superficial tumors with a circular curvature.
TU‐A‐9A‐03: Development and Verification of a Forward Model That Assists in Iterative Post‐Processing Algorithms Used to Reduce Blur in Compton Backscatter Imaging Systems
Authors: Juneja B , Gilland D , Hintenlang D , Doxsee K , Bova F
Published: July 2014

Purpose:

In Compton Backscatter Imaging (CBI), the source and detector reside on the same side of the patient. We previously demonstrated the applicability of CBI systems for medical purposes using an industrial system. To assist in post‐processing images from a CBI system, a forward model based on radiation absorption and scatter principles has been developed.

Methods:

The forward model was developed in C++ using raytracing to track particles. The algorithm accepts phantoms of any size and resolution to calculate the fraction of incident photons scattered back to the detector, and can perform these calculations for any detector geometry and source specification. To validate the model, results were compared to MCNP‐X, which is a Monte Carlo based simulation software, for various combinations of source specifications, detector geometries, and phantom compositions.

Results:

The model verified that the backscatter signal to the detector was based on three interaction probabilities: a) attenuation of photons going into the phantom, b) Compton scatter of photons toward the detector, and c) attenuation of photons coming out of the phantom. The results from the MCNP‐X simulations and the forward model varied from 1 to 5%. This difference was less than 1% for energies higher than 30 keV, but was up to 4% for lower energies. At 50 keV, the difference was less than 1% for multiple detector widths and for both homogeneous and heterogeneous phantoms.

Conclusion:

As part of the optimization of a medical CBI system, an efficient and accurate forward model was constructed in C++ to estimate the output of CBI system. The model characterized individual components contributing to CBI output and increased computational efficiency over Monte Carlo simulations. It is now used in the development of novel post‐processing algorithms that reduce image blur by reversing undesired contribution from outside the region of interest.
TU‐A‐9A‐05: First Experimental Demonstration of the Anisotropic Detection Principle in X‐Ray Fluorescence Computed Tomography
Authors: Ahmad M , Bazalova M , Fahrig R , Xing L
Published: July 2014

Purpose:

To improve the sensitivity of X‐ray fluorescence computed tomography (XFCT) for in vivo molecular imaging. Is the maximum sensitivity achieved with an isotropic (4π) detector configuration? We prove that this is not necessarily true, and that a greater sensitivity is possible with anisotropic detector configuration.

Methods:

An XFCT imaging system was constructed consisting of 1) a collimated pencil beam x‐ray source using a fluoroscopy grade x‐ray tube; 2) a CdTe x‐ray photon counting detector to detect fluorescent x‐rays; and 3) a rotation/translation stage for tomographic imaging. We created a 6.5‐cm diameter water phantom with 2‐cm inserts of low gold concentration (0.25%–1%) to simulate tumors targeted by gold nano‐particles. The placement of x‐ray fluorescence detector were chosen to minimize scatter x‐rays. XFCT imaging was performed at three different detector positions (60°, 90°, 145°) to determine the impact of forward‐scatter, side‐scatter, and back‐scatter on imaging performance. The three data sets were also combined to estimate the imaging performance with an isotropic detector.

Results:

The highest imaging performance was achieved when the XF detector was in the backscatter 145° configuration. The signal‐to‐noise ratio (SNR) was 5.5 for the 0.25% gold concentration compared to SNRs of 1.4, 0, and 2.4 for 60°, 90°, and combined (60°+90°+145°) datasets. Only the 145° detector arrangement alone could detect the 0.25% concentration. The imaging dose was 14 mGy for each detector arrangement experiment.

Conclusion:

This study experimentally proves, for the fist time, the Anisotropic Detection Principle in XF imaging, which holds that optimized anisotropic x‐ray fluorescence detection provides greater sensitivity than isotropic detection. The optimized detection arrangement was used to improve the sensitivity of the XFCT experiment. The achieved XFCT sensitivity is the highest ever for a phantom at least this large using a benchtop x‐ray source, which is an important step toward clinical XFCT molecular imaging.

This work was supported by the NCI fellowship grant R25T‐CA118681 and by the NIH (1R01‐EB016777) and NIBIB (1K99‐EB016059).