Patients Of Different Sizes Research Articles

The determination of coefficients for size specific effective dose for adult and pediatric patients undergoing routine computed tomography examinations.

The effective dose resulting from computed tomography (CT) scans provides an assessment of the risk associated with stochastic effects but does not account for the patient's size. Advances in Monte Carlo simulations offer the potential to obtain organ dose data from phantoms of varying stature, enabling derivation of a size-specific effective doses (SEDs) representing doses to individual patients. This study aimed to compute size-specific k-conversion factors for SED in routine CT examinations for adult and pediatric patients of different sizes. Radiation interactions were simulated for adult and pediatric phantom models of various sizes using National Cancer Institute CT version 3.0.20211123. Subsequent calculations of SED were performed, and coefficients for SED were derived, considering the variations in body sizes. The results revealed a strong correlation between effective diameter and weight, observed with size-specific k-conversion factors for adult and pediatric phantoms, respectively. While size-specific k-conversion factors for CT brain remained constant in adults, values for pediatric cases varied. When using the tube current modulation (TCM) system, size-specific k-conversion factors increased in larger phantoms and decreased in smaller ones. The extent of this increase or decrease correlated with the set TCM strength. This study provides coefficients for estimating SEDs in routine CT exams. Software utilizing look-up tables of coefficients can be used to provide dose information for CT scanners at local hospitals, offering guidance to practitioners on doses to individual patients and improving radiation risk awareness in clinical practice.

Protocol optimization for functional cardiac CT imaging using noise emulation in the raw data domain.

Four-dimensional (4D) wide coverage computed tomography (CT) is an effective imaging modality for measuring the mechanical function of the myocardium. However, repeated CT measurement across a number of heartbeats is still a concern. A projection-domain noise emulation method is presented to generate accurate low-dose (mA modulated) 4D cardiac CT scans from high-dose scans, enabling protocol optimization to deliver sufficient image quality for functional cardiac analysis while using a dose level that is as low as reasonably achievable (ALARA). Given a targeted low-dose mA modulation curve, the proposed noise emulation method injects both quantum and electronic noise of proper magnitude and correlation to the high-dose data in projection domain. A spatially varying (i.e., channel-dependent) detector gain term as well as its calibration method were proposed to further improve the noise emulation accuracy. To determine the ALARA dose threshold, a straightforward projection domain image quality (IQ) metric was proposed that is based on the number of projection rays that do not fall under the non-linear region of the detector response. Experiments were performed to validate the noise emulation method with both phantom and clinical data in terms of visual similarity, contrast-to-noise ratio (CNR), and noise-power spectrum (NPS). For both phantom and clinical data, the low-dose emulated images exhibited similar noise magnitude (CNR difference within 2%), artifacts, and texture to that of the real low-dose images. The proposed channel-dependent detector gain term resulted in additional increase in emulation accuracy. Using the proposed IQ metric, recommended kVp and mA settings were calculated for low dose 4D Cardiac CT acquisitions for patients of different sizes. A detailed method to estimate system-dependent parameters for a raw-data based low dose emulation framework was described. The method produced realistic noise levels, artifacts, and texture with phantom and clinical studies. The proposed low-dose emulation method can be used to prospectively select patient-specific minimal-dose protocols for functional cardiac CT.

Diagnostic performance and feasibility of dual-layer detector dual-energy CT for characterization of urinary stones in patients of different sizes.

Urinary stones are frequently encountered in urology and are typically identified using non-contrast CT scans. Dual-energy CT (DECT) is a valuable imaging technique that produces material-specific images and allows for precise assessment of stone composition by estimating the effective atomic number (Zeff), a capability not achievable with the conventional single-energy CT's attenuation measurement method. To investigate the diagnostic performance and image quality of dual-layer detector DECT (dlDECT) in characterizing urinary stones in patients of different sizes. All consecutive dlDECT examinations with stone protocol and presence of urinary stones between July 2018 and November 2019 were retrospectively evaluated. Two radiologists independently reviewed 120 kVp and color-overlay Zeff images to determine stone composition (reference standard = crystallography) and image quality. The objective analysis included image noise and Zeff values measurement. A total of 739 urinary stones (median size 3.7 mm, range 1-35 mm) were identified on 177 CT examinations from 155 adults (mean age, 57 ± 15 years, 80 men, median weight 82.6 kg, range 42.6-186.9 kg). Using color-overlay Zeff images, the radiologists could subjectively interpret the composition in all stones ≥ 3 mm (n = 491). For stones with available reference standards (n = 74), dlDECT yielded a sensitivity of 80% (95%CI 44-98%) and a specificity of 98% (95%CI 92-100%) in visually discriminating uric acid from non-uric acid stones. Patients weighing > 90 kg and ≤ 90 kg had similar stone characterizability (p = 0.20), with 86% of stones characterized in the > 90 kg group and 87% in the ≤ 90 kg group. All examinations throughout various patients' weights revealed acceptable image quality. A Zeff cutoff of 7.66 accurately distinguished uric acid from non-uric acid stones (AUC = 1.00). Zeff analysis revealed AUCs of 0.78 and 0.91 for differentiating calcium-based stones from other non-uric stones and all stone types, respectively. dlDECT allowed accurate differentiation of uric acid and non-uric acid stones among patients with different body sizes with acceptable image quality. The ability to accurately differentiate uric acid stones from non-uric acid stones using color-overlay Zeff images allows for better tailored treatment strategies, helping to choose appropriate interventions and prevent potential complications related to urinary stones in patient care.

PHANTOM AND CLINICAL STUDIES ON LOW-DOSE CT PROTOCOL FOR APPLICATOR RECONSTRUCTION IN THREE-DIMENSIONAL BRACHYTHERAPY USING SIZE-SPECIFIC DOSE ESTIMATES BASED ON WATER EQUIVALENT DIAMETER.

To verify the feasibility of low-dose computed tomography (CT) protocol for applicator reconstruction in three-dimensional brachytherapy among patients of different sizes, using size-specific dose estimate based on water equivalent diameter (SSDEdw) in phantom and clinical studies. Pre-scans of a female pelvic phantom were followed by reconstruction of each image set with iDose4 levels 3-5. Imaging data from 64 cervical cancer patients were divided into low, standard and high weight groups. Among two to five CT scans required for applicator reconstruction, the first scan was adopted by routine-dose CT protocol (tube voltage = 120 kV, tube current-exposure time product = 320 mA.s) and the remaining by low-dose CT protocol (tube voltage = 120 kV, tube current-exposure time product = 80 mA.s). The SSDEdw and image quality parameters were compared among the groups, and correlations between SSDEdw and body mass index, area of reference plane (AreaROI3) and mean CT value of reference plane (CTROI3) were analyzed. According to the phantom test results, we determined tube voltage to 120 kV and tube current-exposure time product to 80 mA.s as the low-dose protocol. Clinical study revealed no statistically significant differences in signal-to-noise ratio (SNR) and contrast-noise-ratio (CNR) between low-dose and routine-dose CT in Groups A and B; in Group C, these were significantly lower in the former. The SSDEdw was significantly lower under low-dose than routine-dose protocol in all groups, with strong negative correlation with BMI and AreaROI3 in Groups A and B and moderate-to-strong negative correlation in Group C. Because of the characteristics of three-dimensional brachytherapy, in patients with BMI < 24.0 kg per m2, low-dose CT protocol can minimize radiation exposure and achieve precise, individualized treatment.

The impact of ASiR-V on abdominal CT radiation dose and image quality – A phantom study

IntroductionTo investigate how ASiR-V and kVp changes in Computed tomography (CT) affect radiation dose and image quality, when using automatic tube current modulation (ATCM) for different sized phantoms. MethodsA liver-phantom with two different liver inserts (QRM, Moehrendorf, Germany), with extension rings, representing fat, were additionally applied to the phantom to simulate patients of different sizes (small: 30cm diameter, medium: 35cm and large: 40cm). Abdominal scans were performed on a 256 slice CT scanner (GE Healthcare, Milwaukee, WI, USA), with consistent pitch (0.992), rotation time (0.5s), slice thickness (0.625mm) and collimation (80mm), while other parameters were varied (kVp: 80/100/120/140; Noise Index: 13/22; mA interval 80-720, ASiR-V: 30/60/100%). CTDI and DLP was recorded for each scan and image quality was assessed using objective metrics in predefined anatomic areas (HU and noise). Radiation dose and image quality metrics were compared between protocols. ResultsCTDI decreased by 80% from ASIR-V 30% to ASiR-V 100% for prescribed NI 13, and by 79% for the prescribed NI of 22. For 100% ASiR-V and a prescribed NI of 22 the CTDI remained the same regardless of phantom size for the different kVp settings. Pairwise comparison revealed significant differences in CTDI (p < 0.0001) for all combinations of prescribed NI and ASIR-V levels, except the difference between ASIR-V levels of 30 and 60%, with a prescribed NI of 13 (p = 0.124).When data from the three phantom sizes were combined, increasing ASIR-V from 30-100%, resulted in noise decreases of 22% for NI of 13 and by 8% for NI of 22. Notably, image quality in the low contrast area of the liver insert was impaired when the large phantom was scanned with 100% ASiR-V and either 80/100kVp (NI 22), because of the large reduction in tube current applied (down to 80 mA). ConclusionSubstantial radiation dose reductions (up to 80%) resulted from increasing ASiR-V levels. However, image quality deteriorates when 100% ASiR-V is applied due to low applied tube current by the ATCM.

Ultrafiltration Rate Thresholds Associated With Increased Mortality Risk in Hemodialysis, Unscaled or Scaled to Body Size

IntroductionOne proposed threshold ultrafiltration rate (UFR) of concern in hemodialysis patients is 13 ml/h per kg. We evaluated associations among UFR, postdialysis weight, and mortality to determine whether exceeding such a threshold would result in similar levels of risk for patients of different body weights.MethodsData were analyzed in this retrospective cohort study for 1 year following dialysis initiation (baseline) and over 2 years of follow-up in incident patients receiving thrice-weekly in-center hemodialysis. Patient-level UFR was averaged over the baseline period. To investigate the joint effect of UFR and postdialysis weight on survival, we fit Cox proportional hazards models using bivariate tensor product spline functions, adjusting for sex, race, age, diabetes, and predialysis serum albumin, phosphorus, and systolic blood pressure (BP). We constructed contour plots of mortality hazard ratios (MHRs) over the entire range of UFR values and postdialysis weights.ResultsIn the studied 2542 patients, UFR not scaled to body weight was strongly associated with MHR, whereas postdialysis weight was inversely associated with MHR. MHR crossed 1.5 when unscaled UFR exceeded 1000 ml/h, and this relationship was largely independent of postdialysis weight in the range of 80 to 140 kg. A UFR warning level associated with a lower MHR of 1.3 would be 900 ml/h, whereas the UFR associated with an MHR of 1.0 was patient-size dependent. The MHR when exceeding a UFR threshold of 13 ml/h per kg was dependent on patient weight (MHR = 1.20, 1.45, and >2.0 for a 60, 80, and 100 kg patient, respectively).ConclusionUFR thresholds based on unscaled UFR give more uniform risk levels for patients of different sizes than thresholds based on UFR/kg.

Comparison of Application Value of Different Radiation Dose Evaluation Methods in Evaluating Radiation Dose of Adult Thoracic and Abdominal CT Scan.

ObjectiveTo explore the differences among volumetric CT dose index (CTDIvol), body-specific dose assessment (SSDEED) based on effective diameter (ED), and SSDEWED based on water equivalent diameter (WED) in evaluating the radiation dose of adult thoracic and abdominal CT scanning.MethodsFrom January 2021 to October 2021, enhanced chest CT scans of 100 patients and enhanced abdomen CT scans of another 100 patients were collected. According to the body mass index (BMI), they can be divided into groups A and D (BMI < 20 kg/m2), groups B and E (20 kg/m2 ≤ BMI ≤ 24.9 kg/m2), and groups C and F (BMI > 24.9 kg/m2). The CTDIvol, anteroposterior diameter (AP), and the left and rght diameter (LAT) of all the patients were recorded, and the ED, water equivalent diameter (WED), the conversion factor (fsize,ED), (fsize, WED), SSDEED, and SSDEWED were calculated. The differences were compared between the different groups.ResultsThe AP, LAT, ED, and WED of groups B, E, C, and F were higher than those of groups A and D, and those of groups C and F were higher than those of groups B and E (P < 0.05). The fsize,ED and fsize, WED of groups B, E, C, and F are lower than those of groups A and D, and those of groups C and F are lower than those of groups B and E (P < 0.05). CTDIvol, SSDEED, and SSDEWED in groups B, E, C, and F are higher than those in groups A and D, and those in groups C and F are higher than those in groups B and E (p < 0.05). In the same group, patients with chest- and abdomen-enhanced have higher SSDEWED and SSDEED than CTDIvol, patients with chest-enhanced CT scans have higher SSDEWED than SSDEED, and patients with abdomen-enhanced CT scans have higher SSDEED than SSDEWED (P < 0.05).ConclusionCTDIvol and ED-based SSDEED underestimated the radiation dose of the subject exposed, where the patient was actually exposed to a greater dose. However, SSDEWED based on WED considers better the difference in patient size and attenuation characteristics, and can more accurately evaluate the radiation dose received by patients of different sizes during the chest and abdomen CT scan.

Biomechanical analysis of the drilling parameters for early osteonecrosis of the femoral head

Background and objectiveCore decompression is a surgical procedure commonly used to treat the early osteonecrosis of the femoral head. However, It is not known whether different drilling parameters affect postoperative biomechanical strength. This study aimed to analyze the mechanical stability of different drilling locations and diameters of core decompression using finite element analysis. MethodsFinite element models were established based on computed tomography images obtained from five healthy participants, including the different drilling locations (Lesser trochanter: Above, Parallel, and Below) and diameters. Biomechanical parameters including stiffness and stress were evaluated under slow running loads. ResultsAt the same drilling diameter, the femoral stiffness was highest (p < 0.05) in the Above group and lowest in the Below group, while the maximum equivalent stress of the entry area and the necrotic area was highest (p < 0.05) in the Below group and lowest in the Above group. With the increase of drilling diameters, the stiffness decreased and its decreased percentage comparing the preoperative: Above (1.06–8.82%), Parallel (2.51–13.61%), and Below (3.99–15.06%). The maximum equivalent stress of the entry area and necrotic area increased as the drilling diameter increased, and its increased percentage comparing the preoperative, for the entry area: Above (14.11–219.58%), Parallel (35.91–306.37%), and Below (46.12–240.98%); for the necrotic area: Above (13.64–114.69%), Parallel (29.37–187.76%), and Below (44.76–202.10%). The range of safety drilling parameters (SDP) was obtained (Below<9 mm, Parallel<11 mm, and Above<13 mm) by comparing the maximum equivalent stress of two areas and its yield strength. For patients of different sizes and normal bone mineral density (BMD), the maximum equivalent stress of the two areas did not exceed its yield strength using the range of SDP, except for the patients with abnormal BMD (Osteoporosis) or high body mass index (BMI≥28 kg/m2). ConclusionsThe biomechanical properties of early osteonecrosis of the femoral head deceased with increasing drilling diameters parameters, especially at the location below the lesser trochanter. The SDP (Below<9 mm, Parallel<11 mm, and Above<13 mm) is a suitable reference for most patients to perform slow running postoperatively, while it may be not suitable for patients with osteoporosis or obesity.

Effects of different levels of CT iterative reconstruction on low-contrast detectability and radiation dose in patients of different sizes: an anthropomorphic phantom study.

The purpose of this study was to verify the maintenance of low-contrast detectability at different CT dose reduction levels, in patients of different sizes, as a consequence of the application of iterative reconstruction at different strengths combined with tube current modulation. Anthropomorphic abdominal phantoms of two sizes (small and large) were imaged at a fixed noise with iterative algorithm ASIR-V percentages in the range between 0 and 70% and corresponding dose reductions in the range of 0-83%. A total of 1400 images with and without liver low-contrast simulated lesions were evaluated by five radiologists, using the receiver operating characteristics (ROC) paradigm and evaluating the area under the ROC curve (AUC). The human observer results were then compared with AUC obtained with a channelized Hotelling observer (CHO). CNR values were also calculated. For the small phantom, the AUC values lie between 0.90 and 0.93 for human evaluations of images acquired without iterative reconstruction, with 30% ASIR-V and with 50% ASIR-V. The AUC decreased significantly to 0.81 (p = 0.0001) at 70% ASIR-V. The CHO results were in coherence with human observer scores. Also, similar results were observed for the large size phantom. CNR values were stable for the different ASIR-V percentages. The iterative algorithm maintained the low-contrast detectability up to a dose reduction of about 70%, following application of a 50% ASIR-V combined with automatic tube current modulation, regardless of the phantom size. At further dose reductions using greater iterative percentages, a significant decrease in detectability was observed.

Radiation doses and image quality of abdominal CT scans at different patient sizes using spectral detector CT scanner: a phantom and clinical study.

To compare radiation dose and image quality for abdominal CTs performed on a spectral detector CT (SDCT) and a comparable single-energy conventional CT scanner for patients of different sizes. Four semi-anthropomorphic phantoms were scanned on an SDCT (IQon, Philips Healthcare) and a comparable single-energy CT (iCT 256, Philips Healthcare) under matched scan parameters. Image noise and radiation dose were compared. For the HIPAA-compliant, IRB-approved retrospective cohort patient study, radiation dose was compared after adjusting for patient water equivalent diameter. Difference in subjective and objective image quality was assessed on a subset of 50 patients scanned on both scanners by two readers. CTDIvol and noise from SDCT were higher than conventional CT for all phantoms, with a relative difference of 7.8% (range 5.3-14%) for radiation dose and average difference of 9.0% (range 5.5-11%) for noise. 718 SDCT and 937 conventional CT patients were included in the patient study. CTDIvol for SDCT patients tends to be lower for smaller patients (- 2%, 95% confidence interval (- 5%, - 0.2%) for 200mm water equivalent diameter) and higher for larger patients compared to conventional CT (8%, (6%, 11%) for 400mm). No difference was seen for subjective image quality, SNR, CNR, or image noise between the two scanners, except for higher image noise in the portal vein and higher signal in the aorta on SDCT. Radiation dose for abdominal CT performed on SDCT is similar to the dose on a conventional CT for average size patients, lower for smaller patients, and slightly higher for larger patients. Image quality is similar between the two scanners.

Patient and scanner-specific variable acquisition times for whole-body PET/CT imaging

Image quality in positron emission tomography (PET) is limited by the number of detected photons. Heavier patients present higher photon attenuation levels, thus increasing image noise. In this work, we propose a new method that uses the combined patient attenuation/system matrix together with a tracer uptake prediction model to optimize scan times for different bed positions in whole body scans. Our main goal is to achieve consistent noise levels across patients and anatomical regions. We propose to optimize scan times for individual bed positions, for patients of any size, based on the scanner sensitivity and patient-specific attenuation. Variable scan times for every bed position were determined by combining the system matrix, derived from the computed tomography (CT) and the scanner-specific geometric sensitivity profiles, and estimations of the global tracer uptake for each patient. The method was validated with anthropomorphic phantoms and whole-body patient 18F-FDG PET/CT scans, where variable and fixed times were compared. Phantom experiments showed that the proposed method was successful in keeping noise level constant for different attenuation setups. In real patients, image noise variability was reduced to less than one-half compared with conventional fixed-time scans at the expense of a four-fold increase in scan times between the biggest and smallest patients. Our method can homogenize image quality not only across patients of different sizes but also across different bed positions of the same patient.

MON-103 ALLO-HEMODIALYSIS: A NOVEL TREATMENT OPTION FOR PATIENTS WITH ACUTE AND CHRONIC KIDNEY FAILURE IN LIMITED-RESOURCE SETTINGS

Globally, between 2.2 and 7.1 million people may have died prematurely in 2010 because they did not have access to renal replacement therapy (Liyanage, The Lancet 2015). Social, economic, environmental, and technical barriers prevent a wide-spread use of current dialysis technologies. As a nephrology community, we have not yet developed impactful solutions to address this problem. In our research we systematically questioned long-held paradigms and conceptualized a novel treatment option that may have the potential to increase access to renal replacement therapy and reduce the loss of human life owing to kidney failure. We propose “alloHD” as a novel hemodialysis modality. With alloHD, the patient is dialyzed against a healthy subject (“buddy”). The buddy’s healthy kidneys then excrete the solutes and fluid transferred from the patient (Figure 1). Figure 1: Schematic alloHD setup with a pediatric patient (left) and an adult buddy (right). The buddy’s blood is pumped through the dialysate compartment and serves as dialysate; the two blood streams flow in opposite directions. In this version, ultrafiltration is accommodated by speed differentials of the patient-sided pumps. Using urea kinetic modeling, we simulated a wide range of clinically plausible scenarios and calculated the number of weekly alloHD sessions required to attain a target weekly standard Kt/V ≥ 2.0 when dialyzing pediatric and adult patients of different sizes against an adult buddy, using high-flux dialyzers and a treatment time of 4 hours each. We performed multiple alloHD simulations. Table 1 shows four representative results. Note that in these examples the blood flow rate (Qb) is the same for patient and buddy. AlloHD is a potentially life-saving treatment for patients with acute kidney injury (AKI) and end stage kidney disease (ESKD). Clearly, proof-of-concept animal studies are required, and risks for the buddy and patient need to be explored. Virus transfer is unlikely with intact dialyzer fibers, as the smallest known virus is 5x larger than average high-flux dialyzer pores. In AKI, catheters are likely the vascular access of choice for patient and buddy; in ESKD, arterio-venous fistulas are preferred. In addition to medical and technical considerations, a range of ethical and economic questions need to be addressed, e.g. buddy compensation and care delivery models. While we are cognizant of these challenges, we believe that alloHD expands the repertoire of dialysis therapy options, especially in the aftermath of disasters and in regions of the world where renal replacement therapy is currently out of reach for a large segment of the population.

Blood Pressure Evaluation in Dogs by the Method Doppler and Oscillometric

Blood pressure is currently a very important tool for clinical and veterinary surgery, especially in monitoring patients under anesthesia and in emergency situations. Hypertension can cause a number of changes in the body of dogs and cats, especially those who are middle-aged and elderly. In veterinary medicine, the blood pressure can be measured non-invasively and invasively. The non-invasive, or indirect technique, is frequently used during routine examinations since it presents convenience as it can be carried out quickly, although it is less accurate. For this research 245 dogs were selected, with one to ten years of age, of both sexes, castrated and uncastrated of different breeds and body scores. The dogs were weighed and had the body condition score determined using the system of 9 points, being categorized into: Control group, overweight group or obese group. Systolic blood pressure was obtained by non-invasive method using the Doppler flowmeter and the oscillometric method. 48 animals were excluded due to the high variability of values, with systolic blood pressure greater than 160 mm•Hg, as well as uncooperative and/or aggressive patients. There was agreement between both methods in 197 dogs conscious and asymptomatic and, therefore, this study showed that oscillometric method can be used in normotensive patients as the study was conducted in patients of different sizes, breeds, ages, body scores and sexual status.

Optimization of CT calcium scoring doses on the General Electric Discovery single-photon emission computed tomography/CT D670, 8-slice scanner.

Manufacturer-recommended exposure mA was typically resulting in 3–5 times greater patient doses for calcium score scans compared with other dedicated CT scanners at Nottingham University Hospitals. Image noise was used as a measure of image quality in phantom and patient data. The noise was quantified from the standard deviation in Hounsfield units within regions of interest in the myocardium. Noise in phantom data was found to vary linearly with the inverse square root of the applied mAs. It was assumed that a linear relationship would also apply to patient data but it was predicted that the linear gradient would vary between patients owing to differing patient size and composition. This noise model was used to calculate the exposure mA required to achieve a target noise level of 25 Hounsfield units in the myocardium for each patient. To maintain the image quality for patients of different sizes, three measures of size, weight, body mass index (BMI) and lateral dimension, were all tested for goodness of fit to the noise model. It was found that BMI correlated best with the noise model for small patients, and therefore, BMI was chosen as a measure of patient size for the revised mA table. Using this methodology, doses to small patients were reduced by a factor of four compared with manufacturer-recommended settings.

Patient Size-Specific Analysis of Dose Indexes From CT Lung Cancer Screening.

The U.S. Centers for Medicare & Medicaid Services (CMS) recently approved the use of low-dose CT for lung cancer screening and described volumetric CT dose index (CTDIvol) requirements. These were based on the National Lung Screening Trial, which used only fixed-tube-current techniques. The aim of this study was to evaluate dose index data from a lung cancer screening program using automatic exposure control (AEC) techniques to ensure compliance with requirements and to correlate dose index values with patient size. CTDIvol, dose-length product (DLP), and body mass index (BMI) data were collected for 563 lung cancer screening examinations performed with AEC between January 1, 2014, through August 31, 2015. CTDIvol and DLP were analyzed according to the patient's BMI classification. Results were compared with the CMS requirement that the CTDIvol for a standard-sized patient (height, 170 cm; weight, 70 kg) be 3.0 mGy or less, with adjustments for patients of different sizes. For a subset of patients, the average water-equivalent diameter and size-specific dose estimate were estimated. The average CTDIvol for a standard-sized patient was 1.8 mGy, which meets CMS requirements. CTDIvol values were lower for smaller patients and higher for larger patients. Overall, the mean CTDIvol and DLP were 2.1 mGy and 74 mGy⋅cm, respectively. The size-specific dose estimate for the average water-equivalent diameter (27.5 cm) of the patient subset was 2.6 mGy. The screening protocols using AEC resulted in CTDIvol values that were compliant with CMS requirements. CTDIvol values greater than 3.0 mGy were only observed for overweight or obese patients.

Image texture and radiation dose properties in CT.

The aim of this study was to compare image noise properties of GE Discovery HD 750 and Toshiba Aquilion ONE. The uniformity section of a Catphan 600 image quality assurance phantom was scanned with both scanners, at different dose levels and with extension rings simulating patients of different sizes. 36 datasets were obtained and analyzed in terms of noise power spectrum. All the results prove that introduction of extension rings significantly altered the image quality with respect to noise properties. Without extension rings, the Toshiba scanner had lower total visible noise than GE (with GE as reference: FC18 had 82% and FC08 had 80% for 10 mGy, FC18 had 77% and FC08 74% for 15 mGy, FC18 had 80% and FC08 77% for 20 mGy). The total visible noise (TVN) for 20 and 15 mGy were similar for the phantom with the smallest additional extension ring, while Toshiba had higher TVN than GE for the 10 mGy dose level (120% FC18, 110% FC08). For the second and third ring, the GE images had lower TVN than Toshiba images for all dose levels (Toshiba TVN is greater than 155% for all cases). The results indicate that GE potentially has less image noise than Toshiba for larger patients. The Toshiba FC18 kernel had higher TVN than the Toshiba FC08 kernel with additional beam hardening correction for all dose levels and phantom sizes (120%, 107%, and 106% for FC18 compared to 110%, 98%, and 97%, for FC08, for 10, 15 and 20 mGy doses, respectively).PACS number(s): 87.57.Q‐, 87.57.nf, 87.57.C‐

Calculating patient-specific organ doses from adult body CT scans by Monte Carlo analysis using male-individual voxel phantoms.

Computed tomography (CT) dose calculators such as the WAZA-ARI are useful for estimating the radiation dose from CT examination. This study determined correction coefficients for estimating organ doses to patients of any size attended to in daily clinical practice. To this end, the authors constructed voxel phantoms based on the CT images of patients of different size and simulated radiation transport in CT examinations to obtain organ doses using Monte Carlo simulation. The results show that the linear relationship between effective diameter and organ dose can predict patient-specific organ doses. The effective diameter-based prediction can provide accuracy within an error of ±10%, whereas an error of >20% was observed only in the liver and bladder. These results may contribute to practical irradiation dose calculation from a CT examination depending on individual patient size within a certain degree of accuracy.

Polymethyl Methacrylate Phantom on CT Imaging to Evaluate Size-Specific Effective Dose in Pediatric and Adult Body

Background: Computed tomography (CT) scan is very important for the measurement of effective dose. A patient size-dependent factor is used to estimate patient dose from scanner output indices for patients of different sizes. The size dependent factor is used over a range of patient sizes, and extends to adult and pediatric patients as well as obese ones. Objective: This research was performed the estimation of size-specific effective dose during CT scan of brain of patients by using PMMA 16 cm reference phantom for treatment planning. Materials and methods: We were included pediatric and adult body patients and Polymethyl Methacrylate (PMMA) Phantom to evaluate size specific effective dose. We were used AAPM Report No. 204 as protocol in all the works. To measure size specific effective dose, we were used Lateral (LA), anterior posterior (AP), and effective diameter of the patients with reference Phantom PMMA 32 cm on CT imaging. Results: The effective dose had been calculated for different patients after CT scan of head or brain. To estimate the size-specific effective dose, different parameters like (AP), lateral (LAT), AP+LAT dimension, effective diameter, dose length product (DLP) and size specific dose estimate (SSDE) had been calculated. The estimated value of effective dose was in the range of (346-587) mSv. The relations of effective diameter with AP, LAT, AP+LAT dimension, SSDE and age of the patients had been analyzed. Conclusion: By knowing the effective diameter of the slice of patient’s CT image, a doctor can easily estimate the size-specific effective dose for CT scan of the patients. It was also noted that without knowing effective diameter, a doctor or medical physicist can estimate the size-specific effective dose depend on the patient’s age.

The Subzygomatic Triangle

The masseteric nerve is a valuable donor nerve in the management of facial paralysis; however, its location is less familiar to surgeons because this motor nerve is not commonly exposed in other head and neck procedures. Current techniques for masseteric nerve identification rely on physical measurements from surface or bony landmarks that may be unpredictable across patient age, ethnicity, and size. The authors sought to identify a rapid and minimally invasive technique based on surgical anatomy independent of intraoperative physical measurements. A two-phase, fresh-frozen cadaver study was performed followed by a clinical application that included 11 consecutive patients undergoing facial reanimation procedures between May of 2012 and October of 2012. Ten cadavers were dissected and 11 clinical applications are reported. In all dissections, the masseteric nerve was identified through the newly described "subzygomatic triangle." This triangle is formed by the zygomatic arch superiorly, the temporomandibular joint posteriorly, and the frontal branch of the facial nerve inferiorly and anteriorly. This finding was consistent across patient ages (8 to 49 years) and ethnicities. By using the short-scar, minimal dissection approach described in the study, average time to nerve identification was 10.2 minutes during the clinical application. The subzygomatic triangle is a consistent anatomic landmark for rapid, reliable, and minimally invasive identification of the masseteric nerve. Use of the subzygomatic triangle obviates the need for extensive dissection and surgeon reliance on soft-tissue measurements that may vary among patients of different size, sex, or ethnicity. Therapeutic, IV.

SU-E-I-09: Patient Organ Doses from KV-CBCT Acquisitions as Function of Patient Size and Scan Protocols.

To investigate the organ dose dependence on patient size and position resulting from an image guidance procedures. Depending upon the degree of variability between patients, the feasibility tabulating the organ dose based upon patient size and imaging acquisition procedure. Such tables could be useful in estimating and accounting for organ dose resulting from imaging procedures. Monte-Carlo methods were used to calculate radiation dose to the patient resulting from a kV CBCT imaging scan based upon CT image data. A Python program was created to generate DVHs using the calculated 3D dose matrix and the DICOM-RT Structure Set for the patient. A number of head and pelvic CT scans were used in the study, and the resulting DVHs were analyzed to determine the variation of organ dose as a function of patient size. For the head scans in supine position, the average of the mean doses for some organs, along with the standard deviation in those mean doses, are as follows:Brainstem: 0.25cGy +/- 0.02cGyBrain: 0.26cGy +/- 0.01cGyOptic Chiasm: 0.22 +/- 0.03cGyBone: 0.55 +/- 0.04cGyAnterior Skin: 0.13 +/- 0.05cGyPosterior Skin: 0.23 +/- 0.06cGyEye: 0.11cGy +/- 0.05cGyFor Pelvic scans, dose to organs such as rectum, have likewise been shown to have some variation between patients of different sizes. The results show that it is possible to express organ dose as a function of imaging procedure, imaging device, scan location, body size, and orientation. For example, using a standard head scan on an OBI 1.4 system, the dose to the eye ranged from 0.05-0.20cGy, depending upon the patient size. Considering the amount of imaging dose compared to the therapeutic dose, this study indicates that organ dose could be estimated by using tabulated values based upon the scan procedure and patient size.