bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐D‐18C‐04: The Feasibility of Quantifying MRI Contrast Agent in Pulsatile Flowing Blood Using DCE‐MRI
Authors: N Gwilliam M , J Collins D , O Leach M , R Orton M
Published: July 2014

Purpose:

To assess the feasibility of accurately quantifying the concentration of MRI contrast agent (CA) in pulsatile flowing blood by measuring its T1, as is common for the purposes of obtaining a patientspecific arterial input function (AIF). Dynamic contrast enhanced (DCE) – MRI and pharmacokinetic (PK) modelling is widely used to produce measures of vascular function but accurate measurement of the AIF undermines their accuracy. A proposed solution is to measure the T1 of blood in a large vessel using the Fram double flip angle method during the passage of a bolus of CA. This work expands on previous work by assessing pulsatile flow and the changes in T1 seen with a CA bolus.

Methods:

A phantom was developed which used a physiological pump to pass fluid of a known T1 (812ms) through the centre of a head coil of a clinical 1.5T MRI scanner. Measurements were made using high temporal resolution sequences suitable for DCE‐MRI and were used to validate a virtual phantom that simulated the expected errors due to pulsatile flow and bolus of CA concentration changes typically found in patients.

Results:

: Measured and virtual results showed similar trends, although there were differences that may be attributed to the virtual phantom not accurately simulating the spin history of the fluid before entering the imaging volume. The relationship between T1 measurement and flow speed was non‐linear. T1 measurement is compromised by new spins flowing into the imaging volume, not being subject to enough excitations to have reached steady‐state. The virtual phantom demonstrated a range of recorded T1 for various simulated T1 / flow rates.

Conclusion:

T1 measurement of flowing blood using standard DCE‐MRI sequences is very challenging. Measurement error is non‐linear with relation to instantaneous flow speed. Optimising sequence parameters and lowering baseline T1 of blood should be considered.
SU‐D‐12A‐01: An Inter‐Projection Interpolation (IPI) Approach for the Synchronized Moving Grid (SMOG) to Reduce Dose in Cone Beam CT
Authors: Zhang H , Kong V , Ren L , Jin J
Published: July 2014

Purpose:

Synchronized moving grid is a promising technique to reduce scatter and ghost artifacts in cone beam computed tomography (CBCT). However, it requires 2 projections in the same gantry angle to obtain full information due to signal blockage by the grid. We proposed an inter‐projection interpolation (IPI) method to estimate blocked signals, which may reduce the scan time and the dose. This study aims to provide a framework to achieve a balance between speed, dose and image quality.

Methods:

The IPI method is based on the hypothesis that an abrupt signal in a projection can be well predicted by the information in the two immediate neighboring projections if the gantry angle step is small. The study was performed on a Catphan and a head phantom. The SMOG was simulated by erasing the information (filling with “0”) of the areas in each projection corresponding to the grid. An IPI algorithm was applied on each projection to recover the erased information. FDK algorithm was used to reconstruct CBCT images for the IPI‐processed projections, and compared with the original image in term of signal to noise ratio (SNR) measured in the whole reconstruction image range. The effect of gantry angle step was investigated by comparing the CBCT images from projection sets of various gantry intervals, with IPI‐predicted projections to fill the missing projection in the interval.

Results:

The IPI procession time was 1.79s±0.53s for each projection. SNR after IPI was 29.0db and 28.1db for the Catphan and head phantom, respectively, comparing to 15.3db and 22.7db for an inpainting based interpolation technique. SNR was 28.3, 28.3, 21.8, 19.3 and 17.3 db for gantry angle intervals of 1, 1.5, 2, 2.5 and 3 degrees, respectively.

Conclusion:

IPI is feasible to estimate the missing information, and achieve an reasonable CBCT image quality with reduced dose and scan time.

This study is supported by NIH/NCI grant 1R01CA166948‐01
SU‐D‐12A‐04: Investigation of a 2D Antiscatter Grid for Flat Panel Detectors
Authors: Altunbas C , Zhong Y , Shaw C , Kavanagh B , Miften M
Published: July 2014

Purpose:

To improve CT number accuracy and contrast sensitivity, a novel 2D antiscatter grid (ASG) for flat panel detector (FPD) based CBCT imaging was evaluated. Experiments were performed to characterize the scatter rejection and contrast sensitivity performance of ASG. The reduction in primary transmission for various ASG geometries was also evaluated by a computational model.

Methods:

The 2D ASG design was based on multi‐hole collimators used in Nuclear Medicine. It consisted of abutted hexagon shaped apertures with 2.5 mm pitch and 32 mm height, and separated by 0.25 mm thick lead septa. Scatter‐to‐primary ratio (SPR), contrast‐to‐noise ratio (CNR), and mean primary transmission were measured using a benchtop FPD/x‐ray source system. Acrylic slabs of varying thicknesses were imaged with a contrast‐detail phantom to measure CNR and SPR under different scatter conditions. Primary transmission was also measured by averaging pixel values in flood field images without the phantom. We additionally explored variation of primary transmission with pitch and septum thickness using a computational model of our ASG.

Results:

Our 2D ASG reduced the SPR from 3.3 to 0.12, and improved CNR by 50% in 20 cm thick slab phantom projections acquired at 120 kVp. While the measured primary transmission was 72.8%, our simulations show that primary transmission can be increased to 86% by reducing the septum thickness to 0.1 mm. Primary transmission further increases to 93% if septum thickness of 0.1 mm is used in conjunction with an increased pitch of 4 mm.

Conclusion:

The 2D ASG appears to be a promising scatter rejection device, offering both superior scatter rejection and improved contrast sensitivity. Though its lead footprint reduced primary transmission, our work shows that optimization of aperture pitch and septum thickness can significantly improve the primary transmission.
SU‐D‐12A‐06: A Comprehensive Parameter Analysis for Low Dose Cone‐Beam CT Reconstruction
Authors: Lu W , Yan H , Bai T , Zhou L , Gu X , Jiang S , Jia X
Published: July 2014

Purpose:

There is always a parameter in compressive sensing based iterative reconstruction (IR) methods low dose cone‐beam CT (CBCT), which controls the weight of regularization relative to data fidelity. A clear understanding of the relationship between image quality and parameter values is important. The purpose of this study is to investigate this subject based on experimental data and a representative advanced IR algorithm using Tight‐frame (TF) regularization.

Methods:

Three data sets of a Catphan phantom acquired at low, regular and high dose levels are used. For each tests, 90 projections covering a 200‐degree scan range are used for reconstruction. Three different regions‐of‐interest (ROIs) of different contrasts are used to calculate contrast‐to‐noise ratios (CNR) for contrast evaluation. A single point structure is used to measure modulation transfer function (MTF) for spatial‐resolution evaluation. Finally, we analyze CNRs and MTFs to study the relationship between image quality and parameter selections.

Results:

It was found that: 1) there is no universal optimal parameter. The optimal parameter value depends on specific task and dose level. 2) There is a clear trade‐off between CNR and resolution. The parameter for the best CNR is always smaller than that for the best resolution. 3) Optimal parameters are also dose‐specific. Data acquired under a high dose protocol require less regularization, yielding smaller optimal parameter values. 4) Comparing with conventional FDK images, TF‐based CBCT images are better under a certain optimally selected parameters. The advantages are more obvious for low dose data.

Conclusion:

We have investigated the relationship between image quality and parameter values in the TF‐based IR algorithm. Preliminary results indicate optimal parameters are specific to both the task types and dose levels, providing guidance for selecting parameters in advanced IR algorithms.

This work is supported in part by NIH (1R01CA154747‐01)
SU‐E‐E‐03: Developing Solutions to Critical Radiation Oncology Challenges in Tanzania
Authors: Kenton O , Dachi J , Metz J , Avery S
Published: July 2014

Purpose:

Develop solutions to critical medical physics challenges in Tanzania.

Methods:

In September of 2013 we began working with Jumaa Bin Dachi, a Therapy Physicist at the Ocean Road Cancer Institute in Dar es Salaam, Tanzania. We developed a bi‐lateral learning partnership over the course of eight qualitative Skype meetings with Jumaa. From these meetings we have ascertained that there is a gap between the installation of new equipment and treating patients. This gap has often been overlooked by international partners attempting to improve radiation therapy access. Relationships with academic institutions abroad can fill these gaps, and lead to sustained care of patients needing radiation.

Results:

Our efforts are best given in a supporting role to help develop solutions and new technology that can reduce the burden on the Medical Physicist. Solutions may include: training material, support for radiation therapy classes, development of appropriate local protocols, and peer‐review on documents being produced. New technology needs to focus around simple and easy field shaping, improved patient imaging systems, and systems for patient set‐up. We believe our work can help alleviate some of the burdens faced by this institute.

Conclusion:

While we are just in the beginning stage of this partnership, we believe there is great potential for success between both parties. We hope that the Ocean Road Cancer Institute will benefit from potential funding and resources by partnering with a High Income Country to develop affordable solutions to clinical problems in Tanzania.
SU‐E‐E‐06: Teaching Medical Physics in a Radiology Museum
Authors: Bednarek D , Rudin S
Published: July 2014

Purpose:

To enhance the learning process in the teaching of medical physics by providing a venue to experience the historical equipment and devices of radiology.

Methods:

We have created a museum by assembling a large collection of equipment and artifacts related to radiology and medical physics. As part of a learning‐in‐context educational approach, classes for a survey course in medical physics are held in the museum so that students are able to visually and tangibly experience the implements of radiology, while related topics are discussed. The students learn how x‐ray equipment and techniques evolved throughout the years and they learn to appreciate the differences and similarities between current x‐ray technology and that of the early days. The collection contains items dating from the era of the discovery of x‐rays up to recent times and includes gas x‐ray tubes, hand‐held fluoroscopes, generators, spark‐gap kV meters, stereoscopes, glass‐plate radiographs, a photofluorographic unit, wood‐interspaced grid, flat‐panel detector, linear‐accelerator klystron, and brachytherapy radium applicators, as well as an extensive library containing some of the seminal literature of the field so that students can delve deeper into the technology. In addition to the classes, guided tours are provided for radiologic‐technology, bioengineering, physics and medical students, as well as group and individual tours for the general public.

Results:

Student course assessments have consistently included positive expressions of their experience in the museum. Numerous students have volunteered to assist with display preparation and have learned by researching the content. Many individuals have been attracted on a walk‐in basis and have expressed a deep curiosity in the technology, with positive feedback.

Conclusion:

The museum and its artifacts have been invaluable in stimulating interest in the history and technology of medical physics. Students and visitors alike obtain a deeper appreciation of the contribution physics has made to medicine.
SU‐E‐E‐07: When the Old Ways Are the Best Ways: In Defense of Didactic Training
Authors: Sensakovic W
Published: July 2014

Purpose:

Physics education for residents has taken on a more prominent role due to the new ABR examination format. We present a curriculum for a new radiology residency entering its second year. This curriculum favors an extensive traditional didactic teaching approach. The curriculum is designed to minimize the amount of independent learning that is necessary outside the classroom

Methods and Materials:

idactic training repeats yearly for all four years of residency and consists of two 1‐hour lectures per week and several in‐class tests. The impact of physics on clinical practice is introduced gradually throughout the residency using specific clinical cases. The extensive time spent with the residents allows lectures to be taught at a deep (almost physicist) level and reduces the necessity of learning base concepts outside of lecture. This frees the resident to use resources (e.g., AAPM/RSNA physics modules) to cement concepts through repetition or to learn a slightly confusing concept from a different teaching perspective. Consistent testing reduces the traditional resident studying technique of physics “cramming.”

Results:

On average, the first year residents scored in the 98th percentile on the American College of Radiology Diagnostic Radiology In‐Service Training Exam (ACR DXIT). Feedback from the new first year residents was very positive and suggestions are constantly solicited and incorporated. For example, based on resident feedback, short‐format quizzes each lecture were eliminated and replaced interactive questions during lecture. Residents felt they have advanced rapidly and have a better understanding of radiologic physics, though they have expressed concern that the 1‐hour lecture block may not be optimal for learning physics.

Conclusion:

An extensive, physicist‐led series of didactic lectures is effective in the teaching of physics to residents.
SU‐E‐P‐09: Radiation Transmission Measurements and Evaluation of Diagnostic Lead‐Based and Lead‐Free Aprons
Authors: Syh J
Published: July 2014

Purpose:

This study was conducted to ensure that various lead shield apron manufacturers provided accurate attenuation factors regardless of whether the apron was made of lead‐based or lead‐free equivalent material.

Methods:

A calibrated ionization survey meter was placed at chest height and 36 cm horizontally away from a solid water phantom on a simulator couch. Measurements were done with or without apron. Radiation field was set to 24cmx24cm with the phantom at 100cm source‐to‐surface distance. Irradiation time was set for 1 minute at voltages of 60, 80, 100 and 120 kVp. Current was set at 6mA.

Results:

Between 60 kVp and 120 kVp, the transmission through 0.50 mm of lead‐based apron was between 1.0% and 6.5% with a mean value of 3.2% and a standard deviation (s.d.) of 1.4%. The transmissions through the 0.50 mm lead‐free aprons were 1.0 % to 12.0% with a mean value of 6.1% and s.d. of 2.6%. At 120 kVp, the transmission value was 6.5% for 0.50 mm lead‐based apron and 11.1% to 12.0% for 0.50 mm lead‐free aprons. The radiation transmissions at 80 kVp, measured in two different 0.5 mm lead‐free aprons, were 4.3% each. However, only 1.4% transmission was found through the lead‐based apron. Overall, the radiation transmitted through the lead‐based apron was 1/3 transmission of lead‐free at 80kVp, and half value of lead‐free aprons at 100 and 120 kVp.

Conclusion:

Even though lead‐based and lead‐free aprons all claimed to have the same lead equivalent thickness, the transmission might not be the same. The precaution was needed to exercise diligence in quality assurance program to assure adequate protection to staff who wear it during diagnostic procedures. The requirement for aprons not only should be in certain thickness to meet state regulation but also to keep reasonably achievable low exposure with the accurate labeling from manufacturers.
SU‐E‐I‐03: A Kinect‐Based Method of Bone and Soft Tissue Image Separation Using Object Thickness Measurement
Authors: Fukuyoshi R , Kurata T , Sato S , Kozono K , Ono M , Toyofuku F
Published: July 2014

Purpose:

Currently, dual energy subtraction is used for the separation of the soft tissue and bone. There are two methods of calculation: the filter method and the double tube voltage method. However, there are problems with these methods, such as an increase of exposure (double tube voltage method), and image quality degradation due to attenuation of x‐rays (filter method). In the present study, we have developed a new method of separating bone and soft tissue by using a single x‐ray exposure combined with object thickness measurement using the Microsoft Kinect sensor.

Methods:

We used a hand phantom as an object and measured the thickness of the object from a depth image obtained with the Microsoft Kinect. X‐ray images were taken at different tube voltages (40 kV, 60 kV, 80 kV), and thicknesses of the two components were calculated from x‐ray attenuation equation. A software program for an ImageJ Plugin was developed to obtain separated images, and the separated bone image was compared with the original image by visual evaluation and profile data. The thicknesses of the separated phalanx bones were also compared with those measured from CT images.

Results:

It was possible to obtain separated bone and soft tissue images using a single x‐ray exposure. The gray values of the bone were greatly enhanced while those of soft tissue were diminished. A comparison with the CT images showed that the bone thickness error was less than 20.0% in phalanx bones.

Conclusion:

It was shown that the image separation of bone and soft tissue was made possible by using a single x‐ray exposure combined with object thickness measurement. This method will be useful for the accurate evaluation of bone changes after a fracture without using any additional x‐ray exposure.
SU‐E‐I‐05: A Novel Application of SIFT Technique to Microcalcification Detection
Authors: Wang Y , Lin S , Lu C , Lue K , Lai L , Chuang K
Published: July 2014

Purpose:

This work applies Lowe's Scale Invariant Feature Transform (SIFT) to detect micro‐calcification on mammograms. The objective of this study is to expand the function of SIFT, which has originally been used to match objects by matching the detected feature points, and to provide a new method for micro‐calcification detection.

Methods:

First, variables in SIFT, the scaling factor between levels of the image, the radiuses of the areas for maximum comparison within current scale and neighboring scales, and the threshold value for maximum search, were adjusted to allow nearly all the micro‐calcification to be detected as the feature points. Second, to reject feature points which are not micro‐calcification, four features of sixty‐five feature points, determined by physicians as micro‐calcification, curvature of scale space, elements of Hessian matrix, used for the discrimination of prominence and shapes, and Contrast to neighboring pixels, Size on image used to reject points on blob‐like dense tissue, were analyzed to determine the specific ranges for selecting feature points on micro‐calcification.

Results:

Ninety region of interest (ROI) images (268 × 268 pixel) selected from 85 mammograms (3,540 × 4,740 pixel) were employed to test the proposed method. Of the 90 ROI images, 30 images were biopsy‐verified by a physician to present a cluster of micro‐calcification. The other 60 ROI images are selected from normal mammograms. The performance of the study is evaluated by a receiver operating characteristic curve (ROC). An area under the ROC curve of 94.2%, sensitivity of 93.3%, and specificity of 95% was achieved.

Conclusion:

The proposed system based on SIFT accurately detects micro‐calcification in mammograms with various brightness, size, and breast density, without preprocessing them. Our findings merit further investigation for its potential to classify benign and malignant calcification.
SU‐E‐I‐15: Comparison of Radiation Dose for Radiography and EOS in Adolescent Scoliosis Patients
Authors: Schueler B , Walz‐Flannigan A
Published: July 2014

Purpose:

To estimate patient radiation dose for whole spine imaging using EOS, a new biplanar slot‐scanning radiographic system and compare with standard scoliosis radiography.

Methods:

The EOS imaging system (EOS Imaging, Paris, France) consists of two orthogonal x‐ray fan beams which simultaneously acquire frontal and lateral projection images of a standing patient. The patient entrance skin air kerma was measured for each projection image using manufacturer‐recommended exposure parameters for spine imaging. Organ and effective doses were estimated using a commercially‐available Monte Carlo simulation program (PCXMC, STUK, Radiation and Nuclear Safety Authority, Helsinki, Finland) for a 15 year old mathematical phantom model. These results were compared to organ and effective dose estimated for scoliosis radiography using computed radiography (CR) with standard exposure parameters obtained from a survey of pediatric radiographic projections.

Results:

The entrance skin air kerma for EOS was found to be 0.18 mGy and 0.33 mGy for posterior‐anterior (PA) and lateral projections, respectively. This compares to 0.76 mGy and 1.4 mGy for CR, PA and lateral projections. Effective dose for EOS (PA and lateral projections combined) is 0.19 mSv compared to 0.51 mSv for CR.

Conclusion:

The EOS slot‐scanning radiographic system allows for reduced patient radiation dose in scoliosis patients as compared to standard CR radiography.
SU‐E‐I‐16: Comparison of the Blue Part of the Spectral Power Distribution in a Medical Liquid‐Crystal Display for Different Color Temperature Settings
Authors: Akamine H , Kuramoto T , Kato T , Awamoto S , Nakamura Y , Hashimoto N , Morishita J
Published: July 2014

Purpose:

The effects of blue light exposure on visual fatigue have received much attention in recent years. There have been attempts to reduce the blue part of the spectral power distribution in a display's output by using commercial films and glasses. However, reducing the blue part of the spectral power distribution in medical liquid‐crystal displays (LCDs) by changing the color temperature settings may prove to be a simpler solution. Our study aimed to quantitatively compare the blue part of the spectral power distribution of a medical LCD in different color temperature settings.

Materials and Methods:

We used two color LCDs (RadiForce RX340, 400 cd/m2, EIZO). The spectral power distribution, chromaticity, and correlated color temperature were measured for LCDs with different color temperature settings (6500, 7500, and 8500 K). The default color temperature setting of the medical LCDs used in this study was 7500 K. A spectroradiometer (CS‐2000, KONICA MINOLTA) and original gray‐scale test patterns with 18 different luminance levels were used for the measurements.

Results:

The blue parts of the spectral power distribution (380–495 nm) were different for each color temperature setting. The integrated power values over the blue of the spectral power distribution decreased by 9% from 8500 to 7500 K and 13% and from 7500 to 6500 K. The correlated color temperature changed by approximately 1000 K depending on the color temperature setting. The difference in the chromaticity was 0.011 between 8500 and 7500 K and between 7500 and 6500 K.

Conclusion:

Our results quantitatively indicate that the blue part of the spectral power distribution of the medical LCDs tested varies for different settings of color temperature.
SU‐E‐I‐26: Development and Characterization of a Temporally Stable Tissue‐ Mimicking Photoacoustic‐Ultrasonic Phantom
Authors: Mitcham T , Lynch J , Cook J , Emelianov S , Bouchard R
Published: July 2014

Purpose:

To quantify the tissue‐mimicking properties and temporal stability of a novel tissue‐mimicking photoacoustic‐ultrasonic (PAUS) imaging phantom.

Methods:

Nine phantoms containing titanium wire targets were formulated from a Zerdine base with varying degrees of Intralipid and India ink dye to generate distinct scattering and absorption characteristics. India ink was included in three concentrations (0.01%, 0.005%, or 0.0025% by mass), while Intralipid comprised 12.5%, 25%, or 37.5% of the sample by mass. These scattering/absorption agents were combined in a 3×3 matrix to generate unique properties for each phantom. Speed‐of‐sound (SOS), acoustic absorption and optical scattering/absorption measurements were obtained for each formulation to characterize tissuemimicking properties. PAUS imaging was performed on each phantom at four time points, in approximately 2‐month intervals, to assess temporal stability. Images were analyzed to provide data regarding target signal strength, target contrast, signal‐to‐noise ratio (SNR) and contrast‐to‐noise ratio (CNR). All PAUS imaging was performed on a Vevo 2100‐LAZR system (FUJIFILM VisualSonics Inc., Toronto, Canada) at 808 nm using a 20‐MHz US transducer.

Results:

Each phantom formulation provided unique acoustic absorption and optical scattering/absorption; the range of tested formulations provided scattering/absorption/SOS characteristics that accurately mimic tissue. Examination of the longitudinal PAUS data demonstrates that none of the phantoms experienced significant temporal change over the 6‐month testing period. Target signal, contrast, SNR, and CNR changed less than 10% from the initial baseline for an individual phantom through 2, 4, and 6‐month follow‐up imaging sessions.

Conclusion:

This work indicates that the investigated phantom formulations accurately approximate tissue for photoacoustic‐ultrasonic imaging purposes. Additionally, adequate temporal stability is demonstrated over a six‐month period, allowing for construction of a long‐term tissuemimicking PAUS imaging phantom that could be utilized for preclinical technical development or clinical quality assurance purposes in the future. John Lynch is an employee of CIRS, Inc.
SU‐E‐I‐28: Evaluating the Organ Dose From Computed Tomography Using Monte Carlo Calculations
Authors: Ono T , Araki F
Published: July 2014

Purpose:

To evaluate organ doses from computed tomography (CT) using Monte Carlo (MC) calculations.

Methods:

A Philips Brilliance CT scanner (64 slice) was simulated using the GMctdospp (IMPS, Germany) based on the EGSnrc user code. The X‐ray spectra and a bowtie filter for MC simulations were determined to coincide with measurements of half‐value layer (HVL) and off‐center ratio (OCR) profile in air. The MC dose was calibrated from absorbed dose measurements using a Farmer chamber and a cylindrical water phantom. The dose distribution from CT was calculated using patient CT images and organ doses were evaluated from dose volume histograms.

Results:

The HVLs of Al at 80, 100, and 120 kV were 6.3, 7.7, and 8.7 mm, respectively. The calculated HVLs agreed with measurements within 0.3%. The calculated and measured OCR profiles agreed within 3%. For adult head scans (CTDIvol) =51.4 mGy), mean doses for brain stem, eye, and eye lens were 23.2, 34.2, and 37.6 mGy, respectively. For pediatric head scans (CTDIvol =35.6 mGy), mean doses for brain stem, eye, and eye lens were 19.3, 24.5, and 26.8 mGy, respectively. For adult chest scans (CTDIvol=19.0 mGy), mean doses for lung, heart, and spinal cord were 21.1, 22.0, and 15.5 mGy, respectively. For adult abdominal scans (CTDIvol=14.4 mGy), the mean doses for kidney, liver, pancreas, spleen, and spinal cord were 17.4, 16.5, 16.8, 16.8, and 13.1 mGy, respectively. For pediatric abdominal scans (CTDIvol=6.76 mGy), mean doses for kidney, liver, pancreas, spleen, and spinal cord were 8.24, 8.90, 8.17, 8.31, and 6.73 mGy, respectively. In head scan, organ doses were considerably different from CTDIvol values.

Conclusion:

MC dose distributions calculated by using patient CT images are useful to evaluate organ doses absorbed to individual patients.
SU‐E‐I‐32: Improving Vessel Delineation in Brain Using Susceptibility Weighted MRI and Group Sparse Reconstruction
Authors: Stefan W , Hwang K , Hazle J , Stafford R
Published: July 2014

Purpose:

To optimize small vessel delineation on non‐contrast enhanced susceptibility weighted MRI protocol for MRI guided intervention in the brain.

Methods:

Multiple 5mm slices of the brain in a healthy volunteer were acquired with a 16‐echo gradient echo sequence and a 32 channel head coil on a 3T scanner. K‐space was under‐sampled by a factor of 2. Images were reconstructed using 1) the vendor ASSET algorithm, 2) sparsity enforcing TV regularization applied to each slice and echo individually, and 3) group sparse reconstruction on each slice individually but all echoes simultaneously. The group sparse reconstruction increases the signal‐tonoise ratio SNR of later echoes by utilizing the shared edges of brain structure between the echoes, which include the blood vessels. Quantitative PPM maps are computed from the complex images and are post processed by a method that removes background off‐resonance effects. Magnitude images and corrected PPM maps are compared.

Results:

PPM maps show blood vessels with high contrast. The magnitude images and ppm maps using method 1 appear blurry compared to methods 2 and 3 because of anti‐ringing filters. While small vasculatures appear very sharp in the ppm maps of methods 2 and 3, method 3 appears to have less smoothed magnitude images.

Conclusion:

To obtain useful blood vessel delineation, low noise susceptibility weighted images are needed. Standard methods like SWI or SWAN require the combination of several slices using a minimum intensity projection to delineate vessels. The method considered here delineates vasculature with high spatial resolution and high SNR in a single slice. Iterative reconstruction methods have superior image quality but also require much more computation time. By reconstructing all echoes simultaneously, group sparse reconstruction produces the sharpest and clearest images.
SU‐E‐I‐36: Investigation of Geometric Image Distortion Correction Using the Bricks Phantom for Multi‐Modality Imaging
Authors: Hong C , Cho H , Lee D , Ahn B
Published: July 2014

Purpose:

To investigate the feasibility of geometric image distortion correction using the LEGO bricks phantom without plastic container, the geometric MR image distortion was evaluated through the procedure of CT to MR image registration

Method and Materials:

Architecturally stable stacked LEGO bricks phantom, 20 cm in diameter, was scanned on a 1.5 T MRI by using T2 FSE sequence and on a 16 slice CT scanner in the sliceslice mode using 120 kVp and 100 mA. The size of each LEGO brick was 31.60 mm2 including four stud 6.47 mm in inner diameter. The space between stud‐and‐tube couplings of the LEGO bricks were filled with distilled water. The geometric distortion was evaluated based on fiducial arrays and control circles which defined by stud pieces. Control circles were determined by the difference between the diameters of the stud pieces in the MR image and the corresponding diameters of stud pieces in the CT image.

Results:

The fiducial arrays of the LEGO bricks without plastic container were easily visualized in the MR and CT images and there was no water leakage detection within one hour. The control circles were identified and registered. The magnitude of geometric distortion in MR image was gradually increased from near the isocenter to off‐center regions of the magnet, maximum 3%. These results are in good agreement with the standard phantom result.

Conclusions:

The LEGO are inexpensive, good physical accuracy and easy to construct. The bricks are injection molded in Acrylonitrile butadiene styrene (ABS) and are the geometric tolerance with quite tight. However, plastic container for filling with a solution limits clinical applications in terms of flexibility of phantom design. We measured the geometric MR image distortion using the LEGO bricks phantom precisely without plastic container and it can be easily customized for multimodality imaging.
SU‐E‐I‐45: Reconstruction of CT Images From Sparsely‐Sampled Data Using the Logarithmic Barrier Method
Authors: Xu H
Published: July 2014

Purpose:

To develop and investigate whether the logarithmic barrier (LB) method can result in high‐quality reconstructed CT images using sparsely‐sampled noisy projection data

Methods:

The objective function is typically formulated as the sum of the total variation (TV) and a data fidelity (DF) term with a parameter λ that governs the relative weight between them. Finding the optimized value of λ is a critical step for this approach to give satisfactory results. The proposed LB method avoid using λ by constructing the objective function as the sum of the TV and a log function whose augment is the DF term. Newton's method was used to solve the optimization problem. The algorithm was coded in MatLab2013b. Both Shepp‐Logan phantom and a patient lung CT image were used for demonstration of the algorithm. Measured data were simulated by calculating the projection data using radon transform. A Poisson noise model was used to account for the simulated detector noise. The iteration stopped when the difference of the current TV and the previous one was less than 1%.

Results:

Shepp‐Logan phantom reconstruction study shows that filtered back‐projection (FBP) gives high streak artifacts for 30 and 40 projections. Although visually the streak artifacts are less pronounced for 64 and 90 projections in FBP, the 1D pixel profiles indicate that FBP gives noisier reconstructed pixel values than LB does. A lung image reconstruction is presented. It shows that use of 64 projections gives satisfactory reconstructed image quality with regard to noise suppression and sharp edge preservation.

Conclusion:

This study demonstrates that the logarithmic barrier method can be used to reconstruct CT images from sparsely‐amped data. The number of projections around 64 gives a balance between the over‐smoothing of the sharp demarcation and noise suppression. Future study may extend to CBCT reconstruction and improvement on computation speed.
SU‐E‐I‐54: Volumetric Breast Density: Comparison of Estimates From Tomosynthesis Reconstructions with Mammography
Authors: Shi L , Vedantham S , Michaelsen K , Krishnaswamy V , Shenoy A , Pogue B , Karellas A , Paulsen K
Published: July 2014

Purpose:

To measure the volumetric breast density (VBD) from digital breast tomosynthesis (DBT) reconstructions and compare with estimates from mammography.

Methods:

A kernel‐based fuzzy c‐means algorithm developed to segment DBT reconstructed slices to provide anatomic priors for near‐infrared spectroscopy (NIRS) in a multimodality NIRS/DBT clinical‐prototype imaging system was used to quantitate VBD. The VBD was determined from 17 DBT reconstructions of 11 breasts from 9 subjects (6 subjects—unilateral 2‐view, 1 subject—unilateral craniocaudal (CC) view, 2 subjects—bilateral CC view) who underwent multimodality NIRS/DBT imaging. VBD from mammography (Quantra, Hologic Inc.) matched for subject, breast laterality and view was used for comparison. To account for differences in compressed breast thickness (T) between the modalities, the metric normalized VBD (nVBD = VBD/T) was considered.

Results:

All data satisfied normality assumption (Shapiro‐Wilks, p>0.06). Pearson's correlation (r) and paired t‐tests were used for analysis. The normalized VBD (nVBD) was statistically correlated (r=0.66, p<0.01) between the two modalities, but the VBD was not (r=0.47, p=0.06), as the compressed breast thickness (p=0.01, difference=6.6+/−9.8 mm) and the total breast volume (p<0.01, difference=183+/−169 cc) were higher with mammography than with clinical‐prototype NIRS‐coupled DBT system, while the fibroglandular volume was not different (p=0.21). The intra‐modality nVBD assessed between 2‐views of the same breast (n=6) were better correlated (r=0.86, p=0.03) in DBT than in mammography (r=0.57, p=0.24).

Conclusion:

Normalized VBD (nVBD) could be a better metric when compressed breast thickness differs between the modalities. nVBD estimated from DBT is better correlated between 2‐views of the same breast than mammography and could improve the consistency in the estimate. The algorithm, in addition to providing anatomic priors for NIRS reconstruction, may also be suitable for breast density estimation. Ability to use DBT reconstructions could facilitate widespread adaptation. Future studies will investigate VBD from images acquired on a combined mammography/DBT system.

This work was supported in parts by National Institutes of Health (NIH) grants R01CA139449 and R21CA176470. The contents are solely the responsibility of the authors and do not represent the official views of the NIH or the National Cancer Institute.
SU‐E‐I‐71: KVp Dependence of Transmitted Exposure for a Radiography Unit
Authors: Liang Y , Lynch D , So J , Dutta A
Published: July 2014

Purpose:

To investigate the kVp dependence of the transmitted exposure for a radiography x‐ray unit.

Methods:

The study used a GE DiscoveryTM XR656 DR unit, a 30 (L) × 30 (W) × 25 cm thick Lucite phantom, two anthropomorphic phantoms (an Alderson RS‐310 chest phantom and a 3M skull phantom), an Unfors detector, and a Radcal 10×9‐6 ion chamber. We measured the entrance exposure and transmitted exposure of each phantom at 60, 70, 80, 90, 100, 110, 120 kVp for mAs range from 2.5 to 200 mAs, without any additional filter. The FOV is 30×30 cm for the Lucite and chest phantom (AP view), and 20×20 cm for skull phantom (Lateral view). The transmitted exposure was measured at the phantom center of the x‐ray exit side. For chest phantom, the transmitted exposures at 3 inch upper right and upper left from the center were also measured. We also checked the reproducibility and accuracy of the DR unit.

Results:

For each phantom, at every kVp and mAs setting, the transmitted exposure per mAs was calculated and normalized by the relative entrance exposure; the averaged transmitted exposure per mAs at each specific kVp was then determined. For chest phantom, the mean transmitted exposure per mAs was the average of three exit locations. The averaged transmitted exposure per mAs was fit as a power function of kVp. The result showed the transmitted exposure per mAs was approximately proportional to third power of the kVp for two anthropomorphic phantoms and forth power of the kVp for the Lucite phantom.

Conclusion:

The traditional assumption of fifth power kVp dependence to the transmitted exposure is inaccurate. At the normal radiography kVp range, the transmitted exposure is approximately proportional to third power of the kVp for a typical patient and up to forth power of the kVp for a large patient.
SU‐E‐I‐78: Improving Prostatic Delineation Using Dual‐Energy CT
Authors: Gersh J , Fried D
Published: July 2014

Purpose:

Visual prostatic definition is difficult using conventional CT. This is because the prostate is surrounded closely with tissue of similar electron density. Definition is further hindered when the region contains high‐Z material (such as fiducial markers). Dual‐energy CT (DECT) is a technique where images are rendered using two tube voltages during a single scan session. This study evaluates DECT as a means of improving prostatic volume delineation for radiation oncology.

Methods:

The patients were scanned using a Definition AS20 (Siemens Healthcare, Malvern, PA). This device uses a single‐tube configuration, where two scans of differing energies are performed in serial. The scans are acquired with tube voltage of 80kVp and 140kVp. Following acquisition, these scan data were used to generate effective monoenergetic scans ranging from 40keV to 190keV. In the current study, the data were presented to observers using a novel program, which allows real‐time adjustment of window, level, and effective keV; all while scrolling through volumetric slices. Three patients were scanned, each with a different high‐contrast material in or around the prostate: I‐125 seeds, gold fiducial markers, and prostatic calcifications. These images are compared to a weighted average of the 80kVp and 140kVP scans, which yield a scan similar to that of a 120 kVp scan, which is a common tube voltage in radiation oncology.

Results:

Prostatic definition improved in each case. Differentiation of soft tissue from surrounding adipose improved with lower keV, while higher keV provided a reduction of high‐z artifacts. Furthermore, the dynamic adjustment of the keV allowed observers to better recognize regions of differing tissue composition within this relatively homogeneous area.

Conclusion:

By simultaneously providing the observer with the benefits of high‐energy images and low‐energy images, and allowing adjustment in real‐time, improved imaging in highly homogeneous regions such as the male pelvis is achievable.
SU‐E‐I‐80: Beta‐Minus Emitting Radiotracers Improves Molecular Endoscopy
Authors: Carpenter C , Ma X , Sun C , Pratx G , Cheng Z , Xing L
Published: July 2014

Purpose:

Molecular Endoscopy using Cerenkov Luminescence can be used to monitor the distribution of many clinically‐available PET and SPECT probes for endoscopic applications. A main limitation of Cerenkov is its limited sensitivity to small concentrations of radiotracer when using light guides s. Herein we demonstrate that the use of a high energy beta emitting radioisotope, exemplified here with 90Y provides superior sensitivity to 18F because of its higher light output and its lack of corresponding gamma emission.

Methods:

A series of phantom experiments were performed to compare the sensitivity and noise of the CLE system for imaging 90Y and 18F. Three vials of known concentrations of 90Y (0.008 μCi, 0.08 μCi, 1 μCi) were placed in centrifuge tubes and isolated from each other. One vial of 18F (100 μCi) was placed in the imaging chamber and imaged over the course of decay (19 hours, 43 minutes, or ∼10 half‐lives). Image time‐points were formed from 5‐minute integrations.

Results:

Using an SNR of 10 to define the noise‐floor, the 90Y minimum detectable activity was 0.056 μCi. To the contrast, the minimum detectable activity for 18F was 11.63 μCi. These data demonstrate a 207‐fold improvement in SNR of 90Y compared to 18F, when controlled for activity.

Conclusion:

This study demonstrated that a pure β‐ radionuclide such as 90Y be used is superior to 18F for Cerenkov Endoscopy. Further study is needed to demonstrate its utility in preclinical studies, endoscopic applications, intraoperative, and radiotherapy applications.
SU‐E‐I‐88: Mammography Imaging: Does Positioning Matter?
Authors: Zhang J , Szabunio M
Published: July 2014

Purpose:

In mammography, compression is imperative for quality images and glandular radiation exposure dose. The thickness of the compressed breast directly determines mammography acquisition parameters. The compressed thickness varies due to variation in technologist practice, even for the same patient imaged at different time. This study is to investigate potential effect of the variation in breast positioning on radiation dose and image quality.

Methods:

Radiation dose at different thicknesses was measured with a BR‐12 breast phantom for both conventional craniocaudal view and tomosynthesis in a Hologic Tomosynthesis mammography system. The CIRS stereotactic needle biopsy training phantom embedded dense masses and microcalcification in various sizes were imaged for image quality evaluation. Radiologists evaluated images. Clinical mammograms from the same patient but acquired at different time were retrospectively retrieved to evaluate potential effects of variation in positioning.

Results:

Acquisition parameters (kVp and mAs) increase with the increased phantom thickness. Radiation exposure increases following an exponential trend. The stereotactic phantom images showed loss of spatial and contrast resolution with inappropriate positioning. The compressed pressure may not be a good indicator for appropriate positioning. The inclusion of different amount of pectoralis muscle may lead to the same compressed pressure but different compressed thickness. The initial retrospective study of 3 patients showed that there were potential large variations in positioning the same patient at different examination time, resulting in large variations in patient radiation dose and image quality.

Conclusion:

Variations in patient positioning potentially influence patient radiation dose and image quality. The technologist has the critical responsibility to position patient to provide quality images in spite of different breast and body types. To reduce intra and inter practice variations in positioning patient, a training program among each breast imaging center may be a need.
SU‐E‐I‐89: Assessment of CT Radiation Dose and Image Quality for An Automated Tube Potential Selection Algorithm Using Pediatric Anthropomorphic and ACR Phantoms
Authors: Mahmood U , Erdi Y , Wang W
Published: July 2014

Purpose:

To assess the impact of General Electrics automated tube potential algorithm, kV assist (kVa) on radiation dose and image quality, with an emphasis on optimizing protocols based on noise texture.

Methods:

Radiation dose was assessed by inserting optically stimulated luminescence dosimeters (OSLs) throughout the body of a pediatric anthropomorphic phantom (CIRS). The baseline protocol was: 120 kVp, 80 mA, 0.7s rotation time. Image quality was assessed by calculating the contrast to noise ratio (CNR) and noise power spectrum (NPS) from the ACR CT accreditation phantom. CNRs were calculated according to the steps described in ACR CT phantom testing document. NPS was determined by taking the 3D FFT of the uniformity section of the ACR phantom. NPS and CNR were evaluated with and without kVa and for all available adaptive iterative statistical reconstruction (ASiR) settings, ranging from 0 to 100%. Each NPS was also evaluated for its peak frequency difference (PFD) with respect to the baseline protocol.

Results:

For the baseline protocol, CNR was found to decrease from 0.460 ± 0.182 to 0.420 ± 0.057 when kVa was activated. When compared against the baseline protocol, the PFD at ASiR of 40% yielded a decrease in noise magnitude as realized by the increase in CNR = 0.620 ± 0.040. The liver dose decreased by 30% with kVa activation.

Conclusion:

Application of kVa reduces the liver dose up to 30%. However, reduction in image quality for abdominal scans occurs when using the automated tube voltage selection feature at the baseline protocol. As demonstrated by the CNR and NPS analysis, the texture and magnitude of the noise in reconstructed images at ASiR 40% was found to be the same as our baseline images. We have demonstrated that 30% dose reduction is possible when using 40% ASiR with kVa in pediatric patients.