Aluminum Phantom Research Articles

Evaluation of Modular J-PET sensitivity

The Modular J-PET represents the latest advancement in the Jagiellonian-PET series, utilizing extended plastic scintillator strips. This prototype's modular design enables cost-effective imaging of multi-photon annihilation and positronium, allowing for easy assembly, portability, and versatility. Additionally, its lightweight construction facilitates static bed examinations with a mobile detection system that can be positioned conveniently alongside the patient, negating the requirement for spacious clinical settings. Comprising 24 modules arranged in regular 24- sided polygons circumscribing a 73.9 cm diameter circle, each module integrates 13 scintillator strips, measuring 50 cm in length and 6mm×24mm in cross-section. Scintillation light is captured at both ends through analog Silicon Photomultipliers (SiPMs). This research presents Sensitivity of the Modular J-PET tomograph, adhering to the NEMA_NU 2-2018 standards. Sensitivity measurement was performed with 〖^68〗Geline source inside the 5 sleeves aluminium phantom placed at center of the detector`s FOV and 10 cm offset from the center of detector. Analyzing the gathered data involved employing the specialized J-PET Framework software, developed within the C++ architecture. To validate the experimental findings, comparisons were made with GATE simulations, wherein the source and phantom were emulated in the same configuration as employed in the actual experiment.

Feasibility of aluminum phantom radiography for osteoporosis detection in postmenopausal women with a fragility fracture of the distal radius compared toDXA and HR-pQCT.

Recently, promising results have been reported for detection of osteoporosis with use of an aluminum phantom. Therefore, the aim of this study was to evaluate the feasibility of radiography-based bone mineral density (BMD) measurement using a graded aluminum phantom. This study included 27 postmenopausal women with a distal radius fracture. Aluminum phantom radiography of the healthy radius was conducted as well as high-resolution peripheral quantitative computed tomography (HR-pQCT) measurement of the ultradistal radius and dual energy X-ray absorptiometry(DXA) of the radius, spine, and hip. A strong correlation was observed between aluminum phantom radiography-based mean gray value(mGV) and DXA-derived BMD, especially for the ultradistal radius (ρ = 0.75; p < 0.001). A moderate correlation for the femoral neck (ρ = 0.61 and p < 0.001) between modalities was found. Radius mGV and HR-pQCT-derived BMD only showed a moderate correlation (ρ = 0.48; p < 0.09). Aluminum phantom radiography might serve as a cost efficient, highly available, low-radiation dose screening, and diagnostic method for osteoporosis additively to DXAmeasurements. Especially, an application in areas with constrained DXA availability and such as preoperative trauma settings would be beneficial. However, further investigation and assessment of specificity and sensitivity is needed.

Calorimeter measurements of absolute dose in aluminum, a surrogate of bone, to validate dose-to-medium in Acuros XB

Objective. While the accuracy of dose calculations in water with Acuros XB is well established, experimental validation of dose in bone is limited. Acuros XB reports both dose-to-medium and dose-to-water, and these values differ in bone, but there are no reports of measurements of validation in bone. This work compares Acuros XB calculations to measurements of absolute dose in aluminum (medium similar to bone). The validity of using selected relative dosimeters in aluminum is also investigated. Approach. A calorimeter with an aluminum core embedded in an aluminum phantom was selected as bone surrogate for the measurement of absolute dose. Matching the medium of the core to the medium of the phantom allowed eliminating the calculation of the conversion between media. The dose was measured at the fixed depth of 3.3 cm in aluminum (∼9 g·cm−2) with 6X, 10X, 6FFF and 10FFF photon beams from a TrueBeam Varian linac. In addition, experimental cross-calibration between water and aluminum was performed for an IBA CC13 ionization chamber, a PTW microDiamond and EBT3 Gafchromic film. Main results. Calculations with Acuros XB dose-to-medium in aluminum differed from the calorimetry data by −2.8% to −3.5%, depending on the beam. Use of dose-to-water would have resulted in about 39% discrepancy. The cross calibration coefficient between water and aluminum yielded values of about 0.87 for the CC13 chamber, 0.91 for the microDiamond, and 0.88 for the film, and independent of the beam within about ±1%. Significance. It was demonstrated the value of the dose-to-medium in aluminum (surrogate of bone) computed with Acuros XB is close to the value of the absolute dose measured with a calorimeter, and there is a significant discrepancy when dose-to-water is used instead. The use of an ionization chamber, a microDiamond and Gafchromic film in aluminum required a considerable correction from calibration in water.

Use of experimental phantoms to determine the accuracy and reliability of mandibular cortical width measurements by panoramic radiography and cone-beam computed tomography

The present study used an aluminum phantom to calculate accurate vertical magnification values around the mental foramen on panoramic radiography (PR) and compared corrected PR (Cor-PR) thickness measurements of the aluminum phantom and mandibular cortical width (MCW) of the human head with cone-beam computed tomography (CBCT) measurements at two fields of view (FOVs). The calculated vertical magnification value for PR around the mental foramen was 1.37. Measurements of the aluminum phantom significantly differed between Cor-PR and CBCT with an FOV of 100 mm and between CBCT with FOVs of 40 and 100 mm; however, MCW measurements did not significantly differ among the three methods. There was a very strong correlation between Cor-PR and CBCT with an FOV of 40 mm and between CBCT with FOVs of 40 mm and 100 mm, and intraobserver and interobserver agreement was good-to-excellent for all methods. These results suggest that Cor-PR and CBCT with small and large FOVs are acceptable for measuring MCW.

Extending the dynamic range of biomedical micro-computed tomography for application to geomaterials.

X-ray computed tomography (CT) can non-destructively examine objects by producing three-dimensional images of their internal structure. Although the availability of biomedical micro-CT offers the increased access to scanners, CT images of dense objects are susceptible to artifacts particularly due to beam hardening. This study proposes and evaluates a simple semi-empirical correction method for beam hardening and scatter that can be applied to biomedical scanners. Novel calibration phantoms of varying diameters were designed and built from aluminum and poly[methyl-methacrylate]. They were imaged using two biomedical micro-CT scanners. Absorbance measurements made through different phantom sections were fit to polynomial and inversely exponential functions and used to determine linearization parameters. Corrections based on the linearization equations were applied to the projection data before reconstruction. Correction for beam hardening was achieved when applying both scanners with the correction methods to all test objects. Among them, applying polynomial correction method based on the aluminum phantom provided the best improvement. Correction of sample data demonstrated a high agreement of percent-volume composition of dense metallic inclusions between using the Bassikounou meteorite from the micro-CT images (13.7%) and previously published results using the petrographic thin sections (14.6% 8% metal and 6.6% troilite). Semi-empirical linearization of X-ray projection data with custom calibration phantoms allows accurate measurements to be obtained on the radiodense samples after applying the proposed correction method on biomedical micro-CT images.

Dual Energy CBCT Methods to Produce RED, Zeff and Proton RSP Images Using the On-Board Imager of a Linear Accelerator

To present a feasibility study for using dual-energy (DE) cone beam computed tomography (CBCT) to produce relative electron density (RED), effective atomic number (Zeff) and proton relative stopping power (RSP) images, using the on-board imager (OCI) of a commercial linear accelerator. Low- and high-energy (80 kVp and 130 kVp, respectively) CBCT scans of the Catphan 604 phantom were acquired sequentially using the OBI of a commercial Linac. Each acquired projection pair was subsequently decomposed into basis material equivalent thicknesses using a calibration obtained from an aluminum (Al) and polymethyl methacrylate (PMMA) wedge phantom. The Al and PMMA thicknesses projections where then recombined using the linear attenuation coefficient (μ) for each basis material at the desired energy and reconstructed to produce virtual monoenergetic (VM) CBCT images. RED values for each insert of the phantom were obtained by converting the measured μ values for 150 keV VM-CBCT images directly to RED values based on a theoretical μ-RED linear correlation at that energy. The Zeff numbers for each insert were generated using the correlation between the ratio of 40 and 150 keV μ values and the reference Zeff. After obtaining RED and Zeff images, RSP images were obtained using the parametric method proposed by Hunemohr et al. Our theoretical analysis showed good linear correlation (0.9937) between 150 keV μ-values with the reference RED for elements with Z from 6 to 20, with a mean prediction error of 0.000 ± 0.073.The mean RED percentage error for phantom inserts was -0.24% ± 0.75%. The 50% bone insert had the largest percentage error (-1.49%). A logarithmic fit that transforms the ratio of 150/40 keV μ theoretical values to Zeff values from 6 to 20 was also defined. This fit resulted in a correlation coefficient of 0.9979, with a mean prediction error of 0.000 ± 0.021. Applying this data to the phantom inserts, the mean percentage error found for Zeff was 0.08% ± 2.09%. The Teflon insert had the largest percentage error for Zeff estimation (3.44%). The mean percentage RSP error value was -0.19% ± 1.78% with the 50% bone insert having the highest percentage error (-3.74.%). The presented method successfully obtained RED, Zeff and RSP images from VM-CBCT images produced using a sequential DE approach by scanning the phantom directly with the OBI of a commercial linear accelerator. Such an approach may allow for direct verification of RSP values at the time of treatment for proton systems that are equipped with an OBI.

A Cross-Calibration Study of GE Lunar iDXA and GE Lunar DPX Pro for Body Composition Measurements in Children and Adults

Objective: To cross-calibrate dual energy X-ray absorptiometry machines when replacing GE Lunar DPX-Pro with GE Lunar iDXA. Methods: A cross-sectional study was conducted in 126 children (3–19 years) and 135 adults (20–66 years). Phantom cross calibration was carried out using aluminum phantom provided with each of the machines on both machines. Total body less head (TBLH), lumbar spine (L2–L4) and left femoral neck bone mineral density (BMD), bone mineral content (BMC), and bone area were assessed for each patient on both machines. TBLH lean and fat mass were also measured. Bland-Altman analysis, linear regressions, and independent sample t test were performed to evaluate consistency of measurements and to establish cross-calibration equations. Results: iDXA measured 0.33% lower BMD and 0.64% lower BMC with iDXA phantom as compared to DPX-Pro phantom (p < 0.001). In children, TBLH-BMC, femoral BMC and area were measured 10%–14% lesser, TBLH area was higher by 1%–2% and L2–L4 area by 10%–14% by iDXA as compared to DPX-Pro. iDXA measured higher TBLH fat [15% (girls), 31% (boys)] than DPX-Pro. In adults, TBLH-BMD (1.7%–3.4%), BMC (6.0%–10.9%) and area (4.2%–7.6%) were measured lesser by iDXA than DPX-Pro. L2–L4 BMD was higher [2.7% (men), 1.8% (women)] by iDXA than DPX-Pro. Femoral BMC was 2.11% higher in men and 4.1% lower in women by iDXA as compared to DPX-Pro. In children, R2 of cross-calibration equations, ranged from 0.91 to 0.96; in adults, it ranged from 0.93 to 0.99 (p < 0.01). After the regression equations were applied, differences in BMD values between both machines were negligible. Conclusion: A strong agreement for bone mass and body composition was established between both machines. Cross-calibration equations need to be applied to transform DPX-Pro measurements into iDXA measurements to avoid errors in assessment. This study documents a need for use of cross-calibration equations to transform DPX-Pro body composition data into iDXA values for clinical diagnosis.

XSITRAY: A Database for the Detection of Osteoporosis Condition

In the medical era, health of a bone is accessed by the bone mineral density (BMD) test. Bone fracture risk in the humans are estimated or evaluated by the BMD test. The test statement recognizes the presence of signs of presence of the frequent occurring disease in the bone called as osteoporosis. In the earlier stage, the challenge in the BMD measurement is that traditional x-rays are used with a step wedge made from an aluminum or ivory phantom. At each step of the phantom with the known densities, bone content present is intended by a illustration assessment of the density present in the bone. Effectiveness in the value and feasibility in the X-rays compared to cutting-edge methods divulge the potential for novel medical relevance among the investigators. So it is obligatory to enclose a customary database in X-Ray images for the young bud researchers to capture up the dealings to the advance stage by accurate examination of the medical results of the images. The projected X-Ray database is termed XSITRAY, characterizes an early attempt to offer a group of X-Ray images of Spine, Femur, Clavicle, Extremity &amp; Ankle, Extremity &amp; Hand and Knee bones. The details such as age, gender and unique Id of the patient are interpreted in the database.

Assessment of the effect of strontium, lead, and aluminum in bone on dual-energy x-ray absorptiometry and quantitative ultrasound measurements: A phantom study.

Dual-energy X-ray absorptiometry (DXA) is the gold standard technique to measure areal bone mineral density (aBMD) for the diagnosis of osteoporosis. Because DXA relies on the attenuation of photon to estimate aBMD, deposition of bone-seeking metallic elements such as strontium, lead, and aluminum that differ in atomic numbers from calcium can cause inaccurate estimation of aBMD. Quantitative ultrasound (QUS) is another technique available to assess bone health by measuring broadband ultrasound attenuation (BUA), speed of sound (SOS), and an empirically derived quantity called stiffness index (SI). Because the acoustic properties are not prone to significant change due to changes in microscopic atomic composition of bone, it is hypothesized that QUS is unaffected by the presence of bone-seeking elements in the bone. The objective of this study was to investigate the effect of strontium, lead, and aluminum on DXA-derived aBMD and QUS parameters using bone-mimicking phantoms compatible with both techniques. Bone-mimicking phantoms were produced by homogeneously mixing finely powdered hydroxyapatite compounds that contain varying concentrations of strontium, lead, or aluminum with porcine gelatin solution. Seven strontium-substituted phantoms were produced with varying molar ratio of Sr/(Sr + Ca) ranging from 0% to 2%. Four lead-doped phantoms and four aluminum-doped phantoms were constructed with the respective analyte concentrations ranging from 50 to 200 ppm. An additional 0 ppm phantom was produced to be used as a baseline for the lead and aluminum phantom measurements. All phantoms had uniform volumetric bone mineral density (vBMD) of 200 mg/cm3 , and were assessed using a Hologic Horizon® DXA device and a Hologic Sahara® QUS device. Furthermore, theoretical aBMD bias for mol/mol% substitution of calcium with the three bone-seeking elements was calculated. Strong positive linear relationship was found between aBMD measured by DXA and strontium concentration (P < 0.001, r = 0.995). From the measurement of lead and aluminum phantoms using DXA, no statistically significant relationship was observed between aBMD and the analyte concentrations. For the QUS system, with an exception of BUA and lead concentration that exhibited statistically significant relationship (P < 0.038, r = 0.899), no statistically significant change was observed in all QUS parameters with respect to the clinically relevant concentration of all three elements. The calculated theoretical aBMD bias induced by 1 mol/mol% substitution of calcium with strontium, lead, and aluminum were 10.8%, 4.6%, and -0.7%, respectively. aBMD measured by DXA was prone to overestimation in the presence of strontium, but acoustic parameters measured by QUS are independent of strontium concentration. The deviation in aBMD induced by the clinically relevant concentrations of lead and aluminum under 200 ppm could not be detected using the Hologic Horizon® DXA device. Furthermore, the SI measured by the QUS system was not affected by lead or aluminum concentrations used in this study.

Validation of cortical bone mineral density distribution using micro-computed tomography

Changes in the bone mineral density distribution (BMDD), due to disease or drugs, can alter whole bone mechanical properties such as strength, stiffness and toughness. The methods currently available for assessing BMDD are destructive and two-dimensional. Micro-computed tomography (μCT) has been used extensively to quantify the three-dimensional geometry of bone and to measure the mean degree of mineralization, commonly called the tissue mineral density (TMD). The TMD measurement has been validated to ash density; however parameters describing the frequency distribution of TMD have not yet been validated. In the current study we tested the ability of μCT to estimate six BMDD parameters: mean, heterogeneity (assessed by the full-width-at-half-maximum (FWHM) and the coefficient of variation (CoV)), the upper and lower 5% cutoffs of the frequency distribution, and peak mineralization) in rat sized femoral cortical bone samples. We used backscatter scanning electron microscopy (bSEM) as the standard. Aluminum and hydroxyapatite phantoms were used to identify optimal scanner settings (70kVp, and 57μA, with a 1500ms integration time). When using hydroxyapatite samples that spanned a broad range of mineralization levels, high correlations were found between μCT and bSEM for all BMDD parameters (R2≥0.92, p<0.010). When using cortical bone samples from rats and various species machined to mimic rat cortical bone geometry, significant correlations between μCT and bSEM were found for mean mineralization (R2=0.65, p<0.001), peak mineralization (R2=0.61, p<0.001) the lower 5% cutoff (R2=0.62, p<0.001) and the upper 5% cutoff (R2=0.33, p=0.021), but not for heterogeneity, measured by FWHM (R2=0.05, p=0.412) and CoV (R2=0.04, p=0.469). Thus, while mean mineralization and most parameters used to characterize the BMDD can be assessed with μCT in rat sized cortical bone samples, caution should be used when reporting the heterogeneity.

Effect of increased axial rotation angle on bone mineral density measurements of the lumbar spine

Background contextOsteoporosis frequently occurs in elderly people and is commonly associated with neuromuscular diseases or severe cerebral palsy. Osteoporosis can cause pain via compression fractures or secondary neurologic deficits; thus, accurate evaluation of bone mineral density (BMD) is essential for the prevention and treatment of osteoporosis. However, spinal axial rotation caused by scoliosis may affect the outcome of BMD tests, such that BMD measurements may be significantly greater than actual BMD in patients with severe scoliosis of the spine. PurposeWe investigated the effect of axial rotation angle on BMD measurements of the phantom spine. Study design/settingInvestigation for the effect of axial rotation with aluminum phantom spine. MethodsA GE-Lunar Aluminum Spine Phantom was used to assess BMD. Bone mineral content (BMC), BMD, and cross-sectional area were measured 100 times at L1–L4 using a GE Lunar Prodigy Vision system. Dual-energy X-ray absorptiometry was performed at axial rotation angles of 0° to 25° (5° intervals). ResultsCross-sectional area decreased and BMD values increased as the axial rotation angle increased, whereas BMC did not change significantly. A fitting function was obtained to evaluate the relationships among axial rotation angle, cross-sectional area, and BMD. We obtained an equation to estimate BMD at L1–L4: 1.000−0.001674x+0.0001043x2−0.000005333x3, where x denotes the axial rotation angle. We found that the observed BMD needed adjustment when the angle was more than 5°. ConclusionsBone mineral density values may be overestimated in patients with even slight (>5°) axial rotation. When osteoporosis is suspected in a clinical setting, the degree of axial rotation should be measured on a lumbar spine X-ray.

SU-E-I-29: Dose Rate and Image Quality Comparison Between Philips Veradius and GE OEC 9900 Elite Fluoroscopic C-Arms.

The radiation dose rate and image quality were compared on GE OEC 9900 Elite Vas 8 and Philips Veradius fluoroscopic C-arms. Plastic (PMMA) phantoms were used to simulate various thicknesses of soft tissues encountered during fluoroscopically-guided interventional procedures while aluminum and copper phantoms were used to simulate extremities of different sizes. An image quality test tool and an ionization chamber were included in the setup of each phantom. The phantoms were imaged in several fluoroscopy modes and at different dose levels. The entrance surface air KERMA rate (ESAKR) was measured for each phantom in each fluoroscopy mode. Simultaneously, the image quality was assessed by counting the number of low-contrast objects visible in the image quality test tool. For a given phantom type and thickness, the ESAKR was plotted versus the number of visible low-contrast objects to compare the dose rate required for a given level of image quality. Additionally, the mean ESAKR per number of objects was calculated and p-values were used to test for statistically significant differences between the C-arms. For comparable image quality with a given phantom type and thickness the ESAKR with the OEC was typically much higher than with the Veradius. One-tailed, unpaired t-tests confirm that the mean ESAKR per number of visible low-contrast objects was lower for the Veradius than for the OEC with all thicknesses of PMMA (p < 0.05). The differences for the aluminum and copper phantoms were much smaller and were not statistically significant (p-values ranged from 0.2 to 0.47). In general, the Veradius C-arm provided better low-contrast image quality during fluoroscopy, with lower ESAKR than the OEC 9900 Elite Vas 8. The differences were statistically significant only with PMMA phantoms. Funding support provided by Philips Healthcare (Bothell, WA).

SU-GG-I-95: Some Physical and Clinical Factors Influencing the Measurement of Precision Error, Least Significant Change, and Bone Mineral Density in DXA

Purpose: In bone densitometry, Dual‐Energy X‐ray Absorptiometry (DXA) is commonly used to calculate a patient's Bone Mineral Density (BMD) which is used to determine the risk of developing a fracture. The International Society for Clinical Densitometry (ISCD) is the governing body whom sets forth quality control guidelines. Among these guidelines are phantom measurements which are used, for example, to detect any drift in the x‐ray tube . Another necessary aspect of quality control is determining the Least Significant Change (LSC) by completing a precision study. Several factors, both machine and human based, affect the BMD measurement. Our institution performed precision and phantom‐based accuracy studies and compared our results to those of other investigators. Method and Materials: In this work, a GELunar Prodigy Advance DXA was used. For our precision study, 15 patients had BMD measurements both at the PA lumbar spine and total hip (left) by five different technologists. The accuracy study employed custom‐built aluminum lumbar spine phantoms in the shapes of a parallelepiped and trapezoid and were placed each in a basin filled with 15 cm of water. Identical measurements were made also with the vendor supplied phantom. Results: At the 95% confidence level, the calculated LSC's for the spine and hip, respectively are 0.045 g/cm2 and 0.027 g/cm2. The machine calculated measurements of our custom‐built and vendor supplied aluminum phantoms were approximately 40%–50% lower than the physical measurements made in the lab. Conclusion: Based on our results and those reported by other investigators, we conclude that some of the major factors to affect BMD measurements are: precision error is higher for the spine than the hip and the degree of BMD measurement accuracy can be affected by the specific phantom being used as well as faults in edge detection algorithms. Research sponsored by Laurentian University.

Femoral stiffness and strength critically depend on loading angle: a parametric study in a mouse-inbred strain

Biomechanical tests of human femora have shown that small variations of the loading direction result in significant changes in measured bone mechanical properties. However, the heterogeneity in geometrical and bone tissue properties does not make human bones well suited to reproducibly assess the effects of loading direction on stiffness and strength. To precisely quantify the influence of loading direction on stiffness and strength of femora loaded at the femoral head, we tested femora from C57BL/6 inbred mice. We developed an image-based alignment protocol and investigated the loading direction influence on proximal femur stiffness and strength. An aluminum femoral phantom and C57BL/6 femora were tested under compression with different loading directions. Both tests, with the aluminum phantom and the murine bones, showed and quantified the linear dependence of stiffness on loading direction: a 5 degrees change in loading direction resulted in almost 30% change in stiffness. Murine bone testing also revealed and quantified the variation in strength due to loading direction: 5 degrees change in loading direction resulted in 8.5% change in strength. In conclusion, this study quantified, for the first time, the influence of misalignment on bone stiffness and strength for femoral head loading. We showed the extreme sensitivity of this site regarding loading direction.

Development of an Image-Free Navigation Tool for High Tibial Osteotomy

High tibial osteotomy (HTO) is a common therapy for medial gonarthrosis. Intraoperative planning and control of the correction is difficult. Therefore a workflow for a navigation with an image-free navigation system was developed for direct control of the correction of varus/valgus, internal/external rotation, and increase/decrease of the tibial slope. After registration of the lower limb, two k-wires define the osteotomy plane or planes for open- or closed-wedge osteotomy, respectively. The correction is accomplished under navigation system control in real-time. A rigid plate fixation is used for the fixation of the HTO. The reliability and accuracy of the system was approved with an aluminium phantom model.

KNEE SOFT TISSUE TIGHTENING AND ORIENTATION IN INTACT AND PROSTHETIC KNEE IN NAVIGATED TOTAL KNEE ARTHROPLASTY: AN IN-VITRO STUDY

High tibial osteotomy (HTO) is a common therapy for medial gonarthrosis. Intraoperative planning and control of the correction is difficult. Therefore a workflow for a navigation with an image-free navigation system was developed for direct control of the correction of varus/valgus, internal/external rotation, and increase/decrease of the tibial slope. After registration of the lower limb, two k-wires define the osteotomy plane or planes for open- or closed-wedge osteotomy, respectively. The correction is accomplished under navigation system control in real-time. A rigid plate fixation is used for the fixation of the HTO. The reliability and accuracy of the system was approved with an aluminium phantom model.

Calculation of rotational deformity in pediatric supracondylar humerus fractures

Supracondylar humerus fractures (SCHF) are common in the pediatric population. Cubitus varus deformity (CVD) is the most common long-term complication of SCHFs and may lead to elbow instability and deficits in throwing or extension. Distal fragment malrotation in the axial plane disposes to fragment tilt and CVD; however, no simple method of assessing fracture malrotation exists. This study tested a mathematical method of measuring axial plane malrotation in SCHFs based on plain radiographs. A pediatric SCHF model was made, and x-rays were taken at known intervals of rotation. Five independent, blinded observers measured these films. Calculated rotation for each data set was compared to the known rotation. The identical protocol was performed for an aluminum phantom. The reliability and agreement of the rotation values were good for both models. This method is a reliable, accurate, and cost-effective means of calculating SCHF distal fragment malrotation and warrants clinical application.

Imaging properties of cerium doped Yttrium Aluminum Oxide (YAP:Ce) powder scintillating screens under X-ray excitation

The aim of the present study was to evaluate the imaging performance of YAP:Ce powder scintillating screens under exposure conditions employed in diagnostic radiology (50–140 kV). Various screens were prepared in our laboratory from YAP: Ce powder (Phosphor Technology, Ltd.), with coating thickness ranging from 53 to 110 mg/cm 2. The imaging performance of the screens was assessed by experimental determination of the modulation transfer function (MTF) and the noise transfer function (NTF). MTF was determined by the edge spread function (ESF) method while NTF was estimated by noise power spectrum (NPS) measurements after uniform screen irradiation. In addition, parameters related to overall image quality, such as the signal-to-noise ratio transfer (MTF/NTF), were estimated. MTF curves were affected by the beam hardening effects caused by the patient simulating 20 mm thick aluminum phantom. Under these conditions MTF values were found to increase with the mean X-ray photon energy. A similar effect was observed for NTF curves. Results were compared with data obtained on CsI:Tl scintillator. Taking into consideration the very fast response of YAP:Ce, these data may be of interest in designing X-ray imaging detectors.

Effect of Activity and Age on Long Bones Using a New Densitometric Technique

Long bone structural parameters such as cross-sectional area or area moments of inertia are useful measures of long bone mechanical properties. We implemented a three-scan densitometric method to measure structural parameters in long bones of the lower leg in vivo. The validated method was applied to investigate the relationship between activity level, age, and long bone structural parameters in women. An aluminum phantom was used to estimate in vivo setup accuracy. In vivo precision was determined by same-day repeated measures on human subjects. For the activity study, women were recruited in two age groups (25-35, 60+yr) and two activity levels (recreational runners, nonrunners). Scans were taken of the middle third of the lower right leg; structural parameters for the tibia and fibula were determined at each scan line, averaged over the section, and adjusted by factors accounting for body size variations. Aluminum phantom cross-sectional area was underestimated by 4-6%, principal moments were underestimated by <5%, and principal angles were within +/-1.2 degrees. In vivo precision results (lower energy, scans spanning 60 degrees) indicated coefficients of variation for cross-sectional area (A), principal moments of inertia (Imax, Imin), and polar moment of inertia (J) of 0.52, 5.87, 2.22, and 3.82%, respectively. The activity study showed mean adjusted tibial A, Imax, Imin, and J were significantly higher in runners compared with nonrunners. There was no dependence on age. A three-scan densitometric method for measuring cross-sectional structural parameters in long bones in vivo was validated; accuracy and precision measurements establishes confidence limits. From the activity study results, we postulate that higher loads associated with running lead to increased cross-sectional parameters to support axial loads, bending, and torsion in the tibia.

Bone mineral density measures in longitudinal studies: The choice of phantom is crucial for quality assessment. The Tromsø study, a population-based study

Determination of change in bone mineral density (BMD) requires high-precision densitometry techniques. The purpose of the study is to investigate to what degree different densitometer phantoms reflect observed changes in human BMD and to investigate to what degree fluctuations in densitometers' measurement level influence bone loss estimates. Densitometer influence was assessed using the aluminum forearm phantom (AFP) provided by the manufacturer, the European forearm phantom (EFP) of semi-anthropomorphic calcium-hydroxyapatite, and repeated population measurements on different densitometer combinations. The mean follow-up time was 6.4 years (SD 0.6). Measured population bone loss varied from 4.6%/year to 3.2%/year, depending on densitometer combinations. These variations could not be explained by differences in sex, age, height, weight and baseline BMD. They were predicted by EFP measurements, but not AFP measurements. The EFP measurements indicate that X-ray tube replacement changed the densitometers' measurement level in one of three instances, whereas "wear and tear" did not. We used the EFP data for adjustment of the densitometers' measurement levels. After adjustment, the overall crude bone loss was reduced from 4.14% to 3.92%. Mean annual loss was reduced from 0.64% or 0.61%. We conclude that densitometer performance might influence the accuracy of bone loss estimates. Changes in performance are not detected by aluminum phantoms. Quality control of BMD measurements in longitudinal studies should be performed with anthropomorphic calcium-hydroxyapatite phantoms in order to detect possible differences between the participating densitometers' measurement levels.