Toshiba Medical Systems Corporation Research Articles

Spontaneous Bilateral Rectus Abdominis Rhabdomyolysis in a 24-Year Old Male Following Intense Physical Activity in a Sub-Urban Nigerian Town: A Case Report

Introduction: Exercise induced Rhabdomyolysis is a syndrome characterised by disintegration of the skeletal muscles and release of toxic intracellular contents into the plasma. It can be precipitated by strenuous exercise and its diagnosis can easily be missed by physicians. Soft tissue ultrasonography is an invaluable tool for evaluating patients with rhabdomyolysis especially in sub Saharan Africa where sophisticated imaging modalities like magnetic resonance imaging (MRI) and computed tomographic scanners are not readily available. Ultrasonography in this case is the commonly available modality. It is cheap and easier to use. It can aid in the diagnosis of suspected cases, help to determine extent of the disease, identify associated complications and also for monitoring disease progression. Spontaneous rhabdomyolysis following exercise has not been previously reported in our environment. Objectives: To report a case of exercise induced rhabdomyolysis in a 24 year old male patient. To highlight the importance of ultrasound in evaluating patients with rhabdomyolysis, describe the notable ultrasound findings and review relevant existing literature on this condition. Case Report: A 24 year old male with spontaneous rhabdomyolysis of the infra-umbilical segment of both recti abdominis muscles, who presented to a private ultrasound facility in Agbor, Delta state, Nigeria. His symptoms were; lower abdominal pain made worse with movements, and passage of dark red urine which developed spontaneously following a week history of intense physical exercise at a gymnasium. An ultrasound scanner of the Toshiba Medical systems Corp Model 2016 (Xario 100) with a 7 to 12 MHz linear array transducer was used to scan both recti abdominis muscles in different planes. Abnormal findings were noted involving the infra umbilical segment of both abdominal recti muscle belly. Notable findings were thickening of the muscle fascia, blurring of the fat planes, fat stranding, disorganization of the normal architectural pattern of the fibres as well as presence of hypoechoic lesions within the affected muscle segment. The images were frozen and the sonograms were acquired and saved. Conclusion: Ultrasonography is an indispensable tool for evaluating patients with exercise induced spontaneous rhabdomyolysis. This case study is of immense significance in developing affordable methods of image based diagnosis and investigation of rhabdomyolysis that also aids in standard clinical, laboratory and histopathological studies of the condition.

Calculation of Lens Exposure Reduction Using Organ-effective Modulation in Pediatric Head CT

Using a pediatric head phantom constructed in our department, we examined a method to reduce exposure by using organ-effective modulation (OEM; Toshiba Medical Systems Corporation, Tochigi) to tilt the gantry during pediatric head computed tomography (CT) scanning. The radiation reduction and CT image standard deviation (SD) were measured at gantry angles at which the orbit was slightly irradiated, partially irradiated, and completely irradiated. The OEM incident surface dose reduction rate was measured using an automatic exposure control (AEC) phantom with a diameter of 6-18 cm. The lens surface dose reduction rate using OEM was 21.2%. When the gantry was tilted and the orbit was completely out of the scanning range, the rate of reduction was 47.8%. OEM incident surface dose reduction rates were 27.4% for a phantom diameter of 18 cm, 22.0% for that of 16 cm, 17.8% for that of 14 cm, 17.2% for that of 12 cm, 8.4% for that of 10 cm, and 0% for that of 8 cm and 6 cm. OEM effectiveness decreased with decreasing phantom diameter. The use of OEM increased the rate of change of SD by 1.25´ when the gantry inclination was 0°, 1.27´ when the gantry inclination was 10°, and 1.27´ when the gantry inclination was 20°in the 12 o'clock position. The degree of reduction in exposure dose to the lens in pediatric head CT imaging was 47.8% by completely removing the lens from the irradiation range using gantry tilt and 21.2% by using OEM. The effect of OEM changed in proportion to tube current. The exposure reduction effect of the OEM decreases with decreasing head size, indicating its reduced effectiveness in head CT scans of smaller infants.

Analysis of computer tomographic image: skeleto-muscle index as a criterion of sarcopenia in patients with patients with patients

Aim of the study. The study of the possibility and informativeness of the detection of sarcopenia in a patient with pancreatic cancer (PC) by post-processing obtained using computed tomography (CT) images. Materials and methods. A total of 108 patients with obstructive jaundice syndrome (probably of tumor etiology, and later diagnosed with pancreas cancer) were studied using the «Activion 16» spiral tomograph (Toshiba Medical Systems Corporation) according to a common protocol. The control group consisted of 60 patients aged from 22 to 74 years. We determined sarcopenia criteria on CT images: musculoskeletal L3 index (MSI) as the ratio of the area indicator of skeletal muscle in the body to the level L3 square growth patient. The somatotype index (SI) was determined by the formula: SI = BL x 100 / TSCH, where BL is the body length, TSCH is the transverse size of the chest, measurement in centimeters. Results. Based on media values at the L3 level, sarcopenia was generally detected in 85.18 % of patients with pancreas cancer. Sarcopenia was observed in 100 % of patients with a dolichomorphic type, in 87.8 % of patients with a mesomorphic type, and in 65.5 % of patients with a brachiomorphic type of somatotype. Sarcopenia based on SMI at the L3 level is set in 85.2 % of patients with pancreas cancer: 47.8±4.3 cm² / m² for men, 36.2±4.1 cm² / m² for women, 58.4±3 6 cm² / m² and 44.2±3.5 cm² / m² for conditionally healthy men and women, respectively (p<0.01). The reliable differences of SMI according to gender were established in conditionally healthy men and women suffering from pancreatic cancer with inaccurate differences in BMI. In patients, the statistically significant difference of SMI (p = 0.001), corresponds to the various distribution of fatty mass in the body structure, was accompanied by statistical misleading differences in BMI. Findings. CT as a standard method of diagnosis of pancreatic cancer and inflammatory diseases of the pancreas by calculating the SMI allows evaluating the degree of sarcopenia. SMI is more informative and personalized indicators to assess body composition than the standard used BMI as CT allows differentiation of muscle and fat components in the composition of the human body and to quantify

Seeing the Unseen: Evaluating Testicular Vascularity in Neonates by Using the Superb Microvascular Imaging Ultrasound Technique.

To evaluate testicular vascularity in neonates by using the novel Superb Microvascular Imaging (SMI; Toshiba Medical Systems Corporation, Tokyo, Japan) ultrasound (US) technique and to compare this technique to conventional Doppler US techniques. A total of 140 healthy neonates between 2 and 60 days old who were admitted for routine screening were included in the study. However, in 9 cases, the Doppler study could not be completed. In the remaining 131 cases, color Doppler imaging (CDI), power Doppler imaging (PDI), Advanced Dynamic Flow (ADF; Toshiba Medical Systems), and monochrome SMI (mSMI) techniques were performed on a single representative testicle. Real-time cine images were captured for 5 to 10 seconds for each technique by using a high-frequency (7.2-14-MHz) linear transducer. The images were evaluated by 3 observers using a grading system to quantify the degree of vascularity and artifact interference. A total of 131 testicles (74 right and 57 left) were evaluated, and vascularity was shown in 110 (84%) testicles with CDI, 109 (83%) with PDI, 94 (72%) with ADF, and 128 (98%) with mSMI by the consensus of all observers. The Doppler techniques were ranked from highest to lowest in the following order based on the degree of vascularity detected: mSMI > PDI > CDI > ADF (P < .001). Based on the presence of artifacts, the Doppler techniques were ranked as follows from high to low: ADF > CDI > PDI > mSMI (P < .001). Superb Microvascular Imaging is a promising US technique that appears to detect testis vascularity better than conventional Doppler US techniques; however, further research is needed to support the results of this study.

Improvement of CT Imaging with a Metal Artifact Reduction Technique for Radiation Treatment Planning-Fundamental Study of Structure Delineation and Dose Calculation

In radiotherapy planning, CT images are widely used to delineate the gross tumor volume (GTV) and the organs at risks (OARs), which allows for the calculation of the dose distribution to each structure. The delineated contours of the GTV and OARs may become inaccurate, and subsequently result in the inaccurate derivation of the dose distribution, if there are metal artifacts present in the CT image. The metal artifact reduction technique, single energy metal artifact reduction (SEMAR), installed on the CT system (Aquilion ONETM Vision Edition, Toshiba Medical Systems Corporation) could potentially reduce metal artifacts. Therefore, we investigated whether SEMAR can improve the accuracy of delineation, and subsequently the dosimetric accuracy, in the treatment planning process. Using an acrylonitrile-butadiene-styrene resin phantom (RT-3000-New, R-Tech. Inc, Tokyo, Japan), titanium bars were inserted on both the left and right sides, and four types of electron density inserts (rods) were separately inserted in the middle. The electron densities of the rods were 0.90, 0.96, 1.07, and 1.09. After CT images were acquired, SEMAR-ON (when applying the SEMAR correction) images were generated. On both SEMAR-ON and SEMAR-OFF (when not applying the SEMAR correction) images, the rod contours were delineated automatically, using a CT value threshold. This threshold was selected so that the area of the automatically delineated contour was 615.4 mm2. The difference in the contour area of SEMAR-ON, SEMAR-OFF, and no metal artifact images were compared using the dice coefficient. When SEMAR was used, the dice coefficient improved by 57.4%. Therefore, SEMAR was considered to be useful in improving the accuracy of GTV and OAR delineation.

Variability of Liver Shear Wave Measurements Using a New Ultrasound Elastographic Technique.

A new 2-dimensional (2D) shear wave elastographic (SWE) device has been developed for the noninvasive assessment of liver fibrosis. Guidelines on measurement acquisition parameters are not yet well established for this technique. Our study aimed to assess 2D SWE measurement variability and to determine the number of measurements required per patient to reliably assess liver stiffness. Two-dimensional SWE was assessed in 55 patients with mixed-etiology chronic liver disease on an Aplio 500 ultrasound system (Toshiba Medical Systems Corporation, Tochigi, Japan). Ten measurements were obtained per patient by an operator blinded to all preceding readings. Results were analyzed with clinical information obtained from medical records. The median interquartile range/median ratio for 2D SWE was 0.131 (quartiles 1-3, 0.089-0.174). Five readings provided an approximation within 0.11 m/s, or 4.2% of the median velocity of 10 measurements. Factors associated with increased measurement variability included body mass index (ρ = 0.388; P = .01), increased skin-to-liver capsule distance (ρ = 0.426; P = .002), and measurements taken within 1.5 cm of the liver capsule (P < .001). Measurements with heterogeneous shear wave profiles (indicated by a region of interest [ROI] SD/speed ratio > 0.15) showed greater deviation from the set's median velocity than those with an ROI SD/speed ratio of 0.15 or lower (0.42 versus 0.22 m/s; P = .001). Two-dimensional SWE showed low overall measurement variability, with a minimum of 5 readings providing equivalent precision to the existing method using 10 samples. Obesity, increasing abdominal wall thickness, subcapsular measurements and an ROI SD/speed ratio of greater than 0.15 were all associated with increased measurement variability. The ROI SD/speed ratio warrants further evaluation as a quality assessment metric, to allow objective operator assessment of individual 2D SWE measurement reliability in real time.

Diagnostic Performance of Superb Microvascular Imaging and Other Sonographic Modalities in the Assessment of Lateral Epicondylosis.

The aim of this study was to compare the diagnostic performance of different sonographic modalities for diagnosing lateral epicondylosis. A total of 50 symptomatic and 50 asymptomatic common extensor tendons in 44 patients with lateral epicondylosis, and 25 healthy participants were prospectively examined by B-mode sonography, color Doppler imaging, power Doppler imaging, Superb Microvascular Imaging (SMI; Toshiba Medical Systems Corporation, Tokyo, Japan), and strain elastography. We evaluated blood flow in common extensor tendons by using a grading system with color Doppler imaging, power Doppler imaging, and SMI. The diagnostic performance of the modalities was compared. When a cutoff value of hypoechogenicity was used for the mean strain ratio, the sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and accuracy rates were 92.0%, 94%.0, 93.9%, 92.2%, and 93.0%, respectively. When a cutoff point of grade 1 was used, the sensitivity, specificity, PPV, NPV, and accuracy rates were 26.0%, 10.0%, 10.0%, 57.5%, and 63.0, for color Doppler imaging; 40.0%, 10.0%, 10.0%, 62.5%, and 70.0% for power Doppler imaging; and 84.0%, 94.0%, 93.0%, 85.5%, and 89.0% for SMI. When a cutoff value of 3.94 was used for the mean strain ratio, the sensitivity, specificity, PPV, NPV, and accuracy rates were 78.0%, 92.0%, 90.7%, 80.7%, and 85.0%, respectively. A statistically significant correlation was detected between SMI, strain elastography, and visual analog scale scores (P < .001). The combination of SMI and B-mode sonography was found to have excellent diagnostic performance for lateral epicondylosis. Neovascularzation in patients' tendons with lateral epicondylosis was identified much better with SMI compared to color or power Doppler imaging.

Ultrasound Elastography in Pediatric Congenital Hypothyroid Patients.

Congenital hypothyroidism (CH) is most frequently encountered in newborns as an endocrine disorder characterized by thyroid hormone deficiency, and is one of the most common reasons for preventable mental retardation. This prospective study was designed to detect the pediatric occurrences of CH followed as euthyroid, with no anomalies detected via US on the gray scale, in comparison with a pediatric group with normal levels. A total of 42 apparently healthy children with no thyroid disorder (Group 1) and 54 euthyroid CH (Group 2) using thyroid hormone were included in this study. Both B-mode gray scale ultrasound (US) and elastography examinations were made using Toshiba Aplio 400 device (Toshiba Medical Systems Corporation, Otawara, Japan), with a 12 MHz linear probe. All the radiological examinations were made by a single radiologic physician with at least 5 years of experience in elastography. In total, 96 occurrences in the right and left lobes of 192 thyroid gland measurements were included in the research. There were 20 males and 22 females in the healthy group (n=42), and 28 males and 26 females in the CH group (n=54). Although, there were no significant differences in the average age or gender (p=0.563), there were significant differences in the strain index (SI) values in the CH group.The receiver operating characteristics (ROC) curve was done to calculate the cut-off value for diagnosing CH with strain index ratio (SIR); the value of the cut-off was 0.695, with 63.1% sensitivity and 50.9% specificity. This was the first study about CH in children. Our study found the SIR of CH to be higher than the normal thyroid parenchyma. It showed that in parenchymal related CH, SE should be used. This study should be a guide for new studies that should be done about the different etiological factors of CH.

SU‐G‐206‐05: A Comparison of Head Phantoms Used for Dose Determination in Imaging Procedures

Purpose:To determine similarities and differences between various head phantoms that might be used for dose measurements in diagnostic imaging procedures.Methods:We chose four frequently used anthropomorphic head phantoms (SK‐150, PBU‐50, RS‐240T and Alderson Rando), a computational patient phantom (Zubal) and the CTDI head phantom for comparison in our study. We did a CT scan of the head phantoms using the same protocol and compared their dimensions and CT numbers. The scan data was used to calculate dose values for each of the phantoms using EGSnrc Monte Carlo software. An .egsphant file was constructed to describe these phantoms using a Visual C++ program for DOSXYZnrc/EGSnrc simulation. The lens dose was calculated for a simulated CBCT scan using DOSXYZnrc/EGSnrc and the calculated doses were validated with measurements using Gafchromic film and an ionization chamber. Similar calculations and measurements were made for PA radiography to investigate the attenuation and backscatter differences between these phantoms. We used the Zubal phantom as the standard for comparison since it was developed based on a CT scan of a patient.Results:The lens dose for the Alderson Rando phantom is around 9% different than the Zubal phantom, while the lens dose for the PBU‐50 phantom was about 50% higher, possibly because its skull thickness and the density of bone and soft tissue are lower than anthropometric values. The lens dose for the CTDI phantom is about 500% higher because of its totally different structure. The entrance dose profiles are similar for the five anthropomorphic phantoms, while that for the CTDI phantom was distinctly different.Conclusion:The CTDI and PBU‐50 head phantoms have substantially larger lens dose estimates in CBCT. The other four head phantoms have similar entrance dose with backscatter hence should be preferred for dose measurement in imaging procedures of the head.Partial support from NIH Grant R01‐EB002873 and Toshiba Medical Systems Corp.

TU-FG-209-05: Demonstration of the Line Focus Principle Using the Generalized Measured-Relative Object Detectability (GM-ROD) Metric

Purpose: Demonstrate and quantify the augmented resolution due to focalspot size decrease in images acquired on the anode side of the field, for both small and medium (0.3 and 0.6mm) focal-spot sizes using the experimental task-based GM-ROD metric. Theoretical calculations have shown that a medium focal-spot can achieve the resolution of a small focal-spot if acquired with a tilted anode, effectively providing a higher-output small focal-spot. Methods: The MAF-CMOS (micro-angiographic fluoroscopic complementary-metal-oxide semiconductor) detector (75µm pixel pitch) imaged two copper wire segments of different diameter and a pipeline stent at the central axis and on the anode side of the beam, achieved by tilting the x-ray C-arm (Toshiba Infinix) to 6° and realigning the detector with the perpendicular ray to correct for x-ray obliquity. The relative gain in resolution was determined using the GM-ROD metric, which compares images on the basis of the Fourier transform of the image and the measured NNPS. To emphasize the geometric unsharpness, images were acquired at a magnification of two. Results: Images acquired on the anode side were compared to those acquired on the central axis with the same target-area focal-spot to consider the effect of an angled tube, and for all three objects the advantage of the smaller effective focal-spot was clear, showing a maximum improvement of 36% in GM-ROD. The images obtained with the small focal-spot at the central axis were compared to those of the medium focal-spot at the anode side and, for all objects, the relative performance was comparable. Conclusion: For three objects, the GM-ROD demonstrated the advantage of the anode side focal-spot. The comparable performance of the medium focal-spot on the anode side will allow for a high-output small focal-spot; a necessity in endovascular image-guided interventions. Partial support from an NIH grant R01EB002873 and an equipment grant from Toshiba Medical Systems Corp.

MO-FG-CAMPUS-IeP1-04: Kerma Area Product Calculation for Non-Uniform X-Ray Fields Using a Skin Dose Tracking System

Purpose: The functionality of the Dose-Tracking System (DTS) has been expanded to include the calculation of the Kerma-Area Product (KAP) for non-uniform x-ray fields such as result from the use of compensation filters during fluoroscopic procedures Methods: The DTS calculates skin dose during fluoroscopic interventions and provides a color-coded dose map on a patient-graphic model. The KAP is the integral of air kerma over the x-ray field and is usually measured with a transmission-ionization chamber that intercepts the entire x-ray beam. The DTS has been modified to determine KAP when there are beam non-uniformities that can be modeled. For example, the DTS includes models of the three compensation filters with tapered edges located in the collimator assembly of the Toshiba Infinix fluoroscopic C-Arm and can track their movement. To determine the air kerma after the filters, DTS includes transmission factors for the compensation filters as a function of kVp and beam filtration. A virtual KAP dosimeter is simulated in the DTS by an array of graphic vertices; the air kerma at each vertex is corrected by the field non-uniformity, which in this case is the attenuation factor for those rays which pass through the filter. The products of individual vertex air-kerma values for all vertices within the beam times the effective-area-per-vertex are summed for each x-ray pulse to yield the KAP per pulse and the cumulative KAP for the procedure is then calculated. Results: The KAP values estimated by DTS with the compensation filter inserted into the x-ray field agree within ± 6% with the values displayed on the fluoroscopy unit monitor, which are measured with a transmission chamber. Conclusion: The DTS can account for field non-uniformities such as result from the use of compensation filters in calculating KAP and can obviate the need for a KAP transmission ionization chamber. Partial support from NIH Grant R01-EB002873 and Toshiba Medical Systems Corp

TH‐EF‐207A‐03: Photon Counting Implementation Challenges Using An Electron Multiplying Charged‐Coupled Device Based Micro‐CT System

Purpose:To successfully implement and operate a photon counting scheme on an electron multiplying charged‐coupled device (EMCCD) based micro‐CT system.Methods:We built an EMCCD based micro‐CT system and implemented a photon counting scheme. EMCCD detectors use avalanche transfer registries to multiply the input signal far above the readout noise floor. Due to intrinsic differences in the pixel array, using a global threshold for photon counting is not optimal. To address this shortcoming, we generated a threshold array based on sixty dark fields (no x‐ray exposure). We calculated an average matrix and a variance matrix of the dark field sequence. The average matrix was used for the offset correction while the variance matrix was used to set individual pixel thresholds for the photon counting scheme. Three hundred photon counting frames were added for each projection and 360 projections were acquired for each object. The system was used to scan various objects followed by reconstruction using an FDK algorithm.Results:Examination of the projection images and reconstructed slices of the objects indicated clear interior detail free of beam hardening artifacts. This suggests successful implementation of the photon counting scheme on our EMCCD based micro‐CT system.Conclusion:This work indicates that it is possible to implement and operate a photon counting scheme on an EMCCD based micro‐CT system, suggesting that these devices might be able to operate at very low x‐ray exposures in a photon counting mode. Such devices could have future implications in clinical CT protocols.NIH Grant R01EB002873; Toshiba Medical Systems Corp.

SU‐C‐209‐01: Validation of the Simulated Detectability Metric (G‐ROD) Using the Experimental Generalized Measured Relative Object Detectability Metric (GM‐ROD)

Purpose:The Generalized Relative Object Detectability (G‐ROD) family of ideal observer metrics are a well‐characterized set of task‐based metrics used for quantitatively comparing imaging systems that include the detector, focal spot geometry and scatter characteristics on the basis of system abilities in imaging a given simulated object. The G‐ROD metric takes the integral over spatial frequencies of the Fourier transform of a simulated object function weighted with the detector generalized DQE (GDQE), divided by the comparable integral for another detector. When a measured image of an actual object is used, the generalized measured‐ROD (GM‐ROD) metric can compare detector systems without explicitly determining detector MTF. In this work, the results of simulated and measured ROD calculations for the same object are compared for the first time.Methods:G‐ROD calculations were performed to compare a high resolution microangiographic fluoroscopic (MAF) detector to a flat panel detector (FPD) using 5mm segments of simulated copper wires of varying diameter (d=0.05–0.6mm) as the object function for three different focal spot sizes at two magnifications. A GM‐ROD experiment with similar parameters was performed to compare the same detector system using three actual 5mm copper wires (d=0.113mm,0.238mm,0.558mm) imaged under identical but simulated conditions used in G‐ROD calculations to determine the agreement between simulated and experimentally obtained results.Results:The G‐ROD and GM‐ROD calculations examined relative detector system imaging performance. The GM‐ROD results for all three different sized wires imaged with low magnification and a small focal spot size were 2.1, 1.38, and 1.1, respectively, and the G‐ROD results for the same calculation was 1.81, 1.3, and 1.07, corresponding to percent deviations of 13%, 5.8%, and 2.7%.Conclusion:These results indicate experimental validation of the simulated metric results.Partial support from NIH grant R01EB002873 and an equipment grant from Toshiba Medical Systems Corp.

SU‐C‐209‐03: Anti‐Scatter Grid‐Line Artifact Minimization for Removing the Grid Lines for Three Different Grids Used with a High Resolution CMOS Detector

Purpose:Demonstrate the effectiveness of an anti‐scatter grid artifact minimization method by removing the grid‐line artifacts for three different grids when used with a high resolution CMOS detector.Method:Three different stationary x‐ray grids were used with a high resolution CMOS x‐ray detector (Dexela 1207, 75 µm pixels, sensitivity area 11.5cm × 6.5cm) to image a simulated artery block phantom (Nuclear Associates, Stenosis/Aneurysm Artery Block 76–705) combined with a frontal head phantom used as the scattering source. The x‐ray parameters were 98kVp, 200mA, and 16ms for all grids. With all the three grids, two images were acquired: the first for a scatter‐less flat field including the grid and the second of the object with the grid which may still have some scatter transmission. Because scatter has a low spatial frequency distribution, it was represented by an estimated constant value as an initial approximation and subtracted from the image of the object with grid before dividing by an average frame of the grid flat‐field with no scatter. The constant value was iteratively changed to minimize residual grid‐line artifact. This artifact minimization process was used for all the three grids.Results:Anti‐scatter grid lines artifacts were successfully eliminated in all the three final images taken with the three different grids. The image contrast and CNR were also compared before and after the correction, and also compared with those from the image of the object when no grid was used. The corrected images showed an increase in CNR of approximately 28%, 33% and 25% for the three grids, as compared to the images when no grid at all was used.Conclusion:Anti‐scatter grid‐artifact minimization works effectively irrespective of the specifications of the grid when it is used with a high spatial resolution detector.Partial support from NIH Grant R01‐EB002873 and Toshiba Medical Systems Corp.

TU‐D‐209‐02: A Backscatter Point Spread Function for Entrance Skin Dose Determination

Purpose:To determine the distribution of backscattered radiation to the skin resulting from a non‐uniform distribution of primary radiation through convolution with a backscatter point spread function (PSF).Methods:A backscatter PSF is determined using Monte Carlo simulation of a 1 mm primary beam incident on a 30 × 30 cm × 20 cm thick PMMA phantom using EGSnrc software. A primary profile is similarly obtained without the phantom and the difference from the total provides the backscatter profile. This scatter PSF characterizes the backscatter spread for a “point” primary interaction and can be convolved with the entrance primary dose distribution to obtain the total entrance skin dose. The backscatter PSF was integrated into the skin dose tracking system (DTS), a graphical utility for displaying the color‐coded skin dose distribution on a 3D graphic of the patient during interventional fluoroscopic procedures. The backscatter convolution method was validated for the non‐uniform beam resulting from the use of an ROI attenuator. The ROI attenuator is a copper sheet with about 20% primary transmission (0.7 mm thick) containing a circular aperture; this attenuator is placed in the beam to reduce dose in the periphery while maintaining full dose in the region of interest. The DTS calculated primary plus backscatter distribution is compared to that measured with GafChromic film and that calculated using EGSnrc Monte‐Carlo software.Results:The PSF convolution method used in the DTS software was able to account for the spread of backscatter from the ROI region to the region under the attenuator. The skin dose distribution determined using DTS with the ROI attenuator was in good agreement with the distributions measured with Gafchromic film and determined by Monte Carlo simulationConclusion:The PSF convolution technique provides an accurate alternative for entrance skin dose determination with non‐uniform primary x‐ray beams.Partial support from NIH Grant R01‐EB002873 and Toshiba Medical Systems Corp.

TU‐D‐209‐05: Automatic Calculation of Organ and Effective Dose for CBCT and Interventional Fluoroscopic Procedures

Purpose:To compare PCXMC and EGSnrc calculated organ and effective radiation doses from cone‐beam computed tomography (CBCT) and interventional fluoroscopically‐guided procedures using automatic exposure‐event grouping.Methods:For CBCT, we used PCXMC20Rotation.exe to automatically calculate the doses and compared the results to those calculated using EGSnrc with the Zubal patient phantom. For interventional procedures, we use the dose tracking system (DTS) which we previously developed to produce a log file of all geometry and exposure parameters for every x‐ray pulse during a procedure, and the data in the log file is input into PCXMC and EGSnrc for dose calculation. A MATLAB program reads data from the log files and groups similar exposures to reduce calculation time. The definition files are then automatically generated in the format used by PCXMC and EGSnrc. Processing is done at the end of the procedure after all exposures are completed.Results:For the Toshiba Infinix CBCT LCI‐Middle‐Abdominal protocol, most organ doses calculated with PCXMC20Rotation closely matched those calculated with EGSnrc. The effective doses were 33.77 mSv with PCXMC20Rotation and 32.46 mSv with EGSnrc. For a simulated interventional cardiac procedure, similar close agreement in organ dose was obtained between the two codes; the effective doses were 12.02 mSv with PCXMC and 11.35 mSv with EGSnrc. The calculations can be completed on a PC without manual intervention in less than 15 minutes with PCXMC and in about 10 hours with EGSnrc, depending on the level of data grouping and accuracy desired.Conclusion:Effective dose and most organ doses in CBCT and interventional radiology calculated by PCXMC closely match those calculated by EGSnrc. Data grouping, which can be done automatically, makes the calculation time with PCXMC on a standard PC acceptable. This capability expands the dose information that can be provided by the DTS.Partial support from NIH Grant R01‐EB002873 and Toshiba Medical Systems Corp.

TU‐D‐209‐03: Alignment of the Patient Graphic Model Using Fluoroscopic Images for Skin Dose Mapping

Purpose:The Dose Tracking System (DTS) was developed to provide realtime feedback of skin dose and dose rate during interventional fluoroscopic procedures. A color map on a 3D graphic of the patient represents the cumulative dose distribution on the skin. Automated image correlation algorithms are described which use the fluoroscopic procedure images to align and scale the patient graphic for more accurate dose mapping.Methods:Currently, the DTS employs manual patient graphic selection and alignment. To improve the accuracy of dose mapping and automate the software, various methods are explored to extract information about the beam location and patient morphology from the procedure images. To match patient anatomy with a reference projection image, preprocessing is first used, including edge enhancement, edge detection, and contour detection. Template matching algorithms from OpenCV are then employed to find the location of the beam. Once a match is found, the reference graphic is scaled and rotated to fit the patient, using image registration correlation functions in Matlab. The algorithm runs correlation functions for all points and maps all correlation confidences to a surface map. The highest point of correlation is used for alignment and scaling. The transformation data is saved for later model scaling.Results:Anatomic recognition is used to find matching features between model and image and image registration correlation provides for alignment and scaling at any rotation angle with less than onesecond runtime, and at noise levels in excess of 150% of those found in normal procedures.Conclusion:The algorithm provides the necessary scaling and alignment tools to improve the accuracy of dose distribution mapping on the patient graphic with the DTS.Partial support from NIH Grant R01‐EB002873 and Toshiba Medical Systems Corp.

TU-FG-209-10: Phantom Simulation Method to Evaluate the Clinical Utility of the High-Resolution Micro-Angiographic Fluoroscope Complementary Metal Oxide Semiconductor (MAF-CMOS) Detector

Purpose: The purpose of this study is to develop a method to evaluate the clinical utility of a high resolution 75µ pixel MAF-CMOS image receptor compared to a 200µ flat-panel detector (FPD). Methods: A simulated procedure evaluation method was developed using an aneurysm phantom since every clinical device-deployment procedure is different and to faithfully compare the performance of two detectors in a clinical setting would require the device deployment to be stopped at different stages so that images could be acquired with both detectors. Not only is this extremely challenging to implement for a large case cohort, it also requires additional exposure and risk to the patient. To simulate a treatment procedure, a 3D printed aneurysm phantom based on patient morphology was used. An anthropomorphic head phantom was placed underneath the aneurysm phantom to simulate patient attenuation and anatomical features. An endovascular coil was deployed into the aneurysm under the guidance of both the MAF-CMOS and the FPD. To qualitatively evaluate the performance of the detectors based on images, a questionnaire containing visualization criteria was developed and a grading scale from 1 (lowest) to 10 (highest) was assigned to each question. The images from these procedures along with the questionnaire will be presented to observers to qualitatively evaluate and compare the performance of the two detectors. Results: Realistic clinical interventions were simulated using a patient-specific aneurysm phantom. Using a common set of criteria in a questionnaire to individually evaluate these images and then comparing the results for a large cohort can be an effective method to determine the significance of using the MAF-CMOS detector during clinical procedures. Conclusion: The above method can be used to effectively evaluate the clinical utility of the MAF-CMOS detector without additional risk to the patient. partial support from NIH Grant R01-EB002873 and equipment grant from Toshiba Medical Systems Corp.

TU-FG-209-02: Effective Elimination of Aliased Signal Using An Apodized Aperture Pixel Design

Purpose: Signal and noise aliasing are major issues with high resolution direct and indirect detectors for which the Apodized Aperture Pixel (AAP) design provides an alternative solution. Methods: High resolution detectors for neurovascular interventions have MTFs that remain significant even at the Nyquist frequency. Under-sampling in such detectors, leads to aliasing of object frequencies and noise. Frequencies above the Nyquist wrap into the lower frequency range leading to aliasing. The conventional approach of convolving images with low-pass filters such as pixel binning helps in noise reduction but still allows aliasing. The AAP design proposed by Cunningham et.al, uses super sampled images with subpixels from a high resolution detector, convolved with a sinc function to get an image of the desired pixel size while apodizing the MTF beyond the Nyquist. The performance of the AAP filter in eliminating signal aliasing with respect to a standard filter such as simple 2x pixel binning are compared. Results: Three detectors were considered for this study including two indirect detectors with varying thickness of CsI (350µm, HR) and 500µm, HL) and a direct detector (aSe - 1000µm thickness – MTF after Rivetti et.al,). The presampled MTFs of respective detectors were convolved with a 2x pixel binning kernel and the AAP filter. The Fourier transform of an AAP filter, being the box function, the MTF remains high, up to Nyquist and then drops off drastically to zero. Detailed comparisons of resulting MTFs along with the original presampled MTF are shown. The AAP filter resulted in the least degradation of spatial resolution while eliminating aliasing thus outperforming 2x pixel binning Conclusion: In neurovascular imaging using high resolution detectors, the AAP design provides a viable option to effectively remove signal aliasing without compromising high spatial resolution. Partial support from NIH Grant R01-EB002873 and Toshiba Medical Systems Corp.

TU‐H‐CAMPUS‐IeP3‐02: Neurovascular 4D Parametric Imaging Using Co‐Registration of Biplane DSA Sequences with 3D Vascular Geometry Obtained From Cone Beam CT

Purpose:To create 4D parametric images using biplane Digital Subtraction Angiography (DSA) sequences co‐registered with the 3D vascular geometry obtained from Cone Beam‐CT (CBCT).Methods:We investigated a method to derive multiple 4D Parametric Imaging (PI) maps using only one CBCT acquisition. During this procedure a 3D‐DSA geometry is stored and used subsequently for all 4D images. Each time a biplane DSA is acquired, we calculate 2D parametric maps of Bolus Arrival Time (BAT), Mean Transit Time (MTT) and Time to Peak (TTP). Arterial segments which are nearly parallel with one of the biplane imaging planes in the 2D parametric maps are co‐registered with the 3D geometry. The values in the remaining vascular network are found using spline interpolation since the points chosen for co‐registration on the vasculature are discrete and remaining regions need to be interpolated. To evaluate the method we used a patient CT volume data set for 3D printing a neurovascular phantom containing a complete Circle of Willis. We connected the phantom to a flow loop with a peristaltic pump, simulating physiological flow conditions. Contrast media was injected with an automatic injector at 10 ml/sec. Images were acquired with a Toshiba Infinix C‐arm and 4D parametric image maps of the vasculature were calculated.Results:4D BAT, MTT, and TTP parametric image maps of the Circle of Willis were derived. We generated color‐coded 3D geometries which avoided artifacts due to vessel overlap or foreshortening in the projection direction.Conclusion:The software was tested successfully and multiple 4D parametric images were obtained from biplane DSA sequences without the need to acquire additional 3D‐DSA runs. This can benefit the patient by reducing the contrast media and the radiation dose normally associated with these procedures.Partial support from NIH Grant R01‐EB002873 and Toshiba Medical Systems Corp.