A spiculated mass target model for clinical image quality control in digital mammography.

OBJECTIVES: Quality assurance of breast imaging has a long history of using test objects to optimize and follow up imaging devices. In particular, the evaluation of new techniques benefits from suitable test objects. The applicability of a phantom consisting of spiculated masses to assess image quality and its dependence on dose in flat field digital mammography (FFDM) and digital breast tomosynthesis systems (DBT) is investigated. METHODS: Two spiculated masses in five different sizes each were created from a database of clinical tumour models. The masses were produced using 3D printing and embedded into a cuboid phantom. Image quality is determined by the number of spicules identified by human observers. RESULTS: The results suggest that the effect of dose on spicule detection is limited especially in cases with smaller objects and probably hidden by the inter-reader variability. Here, an average relative inter-reader variation of the counted number of 31% was found (maximum 83%). The mean relative intra-reader variability was found to be 17%. In DBT, sufficiently good results were obtained only for the largest masses. CONCLUSIONS: It is possible to integrate spiculated masses into a cuboid phantom. It is easy to print and should allow a direct and prompt evaluation of the quality status of the device by counting visible spicules. Human readout presented the major uncertainty in this study, indicating that automated readout may improve the reproducibility and consistency of the results considerably. ADVANCES IN KNOWLEDGE: A cuboid phantom including clinical objects as spiculated lesion models for visual assessing the image quality in FFDM and DBT was developed and is introduced in this work. The evaluation of image quality works best with the two larger masses with 21 spicules.

Technical note: Realization and uncertainty analysis for an adjustable 3D structured breast phantom in digital breast tomosynthesis.

BACKGROUND: Projection imaging phantoms are often optimized for 2-dimensional image characteristics in homogeneous backgrounds. Therefore, evaluation of image quality in tomosynthesis (DBT) lacks accepted and established phantoms. PURPOSE: We describe a 3D breast phantom with a structured, variable background. The phantom is an adaptable and advanced version of the L1 phantom by Cockmartin et al. Phantom design and its use for quality assurance measurements for DBT devices are described. Four phantoms were compared to assess the objectivity. METHODS: The container size was increased to a diameter of 24 cm and a total height of 53.5 mm. Spiculated masses were replaced by five additional non-spiculated masses for higher granularity in threshold diameter resolution. These patterns are adjustable to the imaging device. The masses were printed in one session with a base layer using two-component 3D printing. New materials compared to the L1 phantom improved the attenuation difference between the lesion models and the background. Four phantoms were built and intra-human observer, inter-human observer and inter-phantom variations were determined. The latter assess the reproducibility of the phantom production. Coefficients of variance (V) were calculated for all three variations. RESULTS: The difference of the attenuation coefficients between the lesion models and the background was 0.20 cm-1 (with W/Al at 32 kV, equivalent to 19-20 keV effective energy) compared to 0.21 cm-1 for 50/50 glandular/adipose breast tissue and cancerous lesions. PMMA equivalent thickness of the phantom was 47.0 mm for the Siemens Mammomat Revelation. For the masses, the V i n t r a $V_{intra}$ for the intra-observer variation was 0.248, the averaged inter-observer variation, V ¯ i n t e r $\overline{V}_{inter}$ was 0.383. V p h a n t o m $V_{phantom}$ for phantom variance was 0.321. For the micro-calcifications, V i n t r a $V_{intra}$ was 0.0429, V ¯ i n t e r = $\overline{V}_{inter}=$ 0.0731 and V p h a n t o m = $V_{phantom}=$ 0.0759. CONCLUSIONS: Position, orientation and shape of the masses are reproducible and attenuation differences appropriate. The phantom presented proved to be a candidate test object for quality control.

Realistic 3D printed CT imaging tumor phantoms for validation of image processing algorithms.

Medical imaging phantoms are widely used for validation and verification of imaging systems and algorithms in surgical guidance and radiation oncology procedures. Especially, for the performance evaluation of new algorithms in the field of medical imaging, manufactured phantoms need to replicate specific properties of the human body, e.g., tissue morphology and radiological properties. Additive manufacturing (AM) technology provides an inexpensive opportunity for accurate anatomical replication with customization capabilities. In this study, we proposed a simple and cheap protocol using Fused Deposition Modeling (FDM) technology to manufacture realistic tumor phantoms based on the filament 3D printing technology. Tumor phantoms with both homogenous and heterogeneous radiodensity were fabricated. The radiodensity similarity between the printed tumor models and real tumor data from CT images of lung cancer patients was evaluated. Additionally, it was investigated whether a heterogeneity in the 3D printed tumor phantoms as observed in the tumor patient data had an influence on the validation of image registration algorithms. A radiodensity range between -217 to 226 HUs was achieved for 3D printed phantoms using different filament materials; this range of radiation attenuation is also observed in the human lung tumor tissue. The resulted HU range could serve as a lookup-table for researchers and phantom manufactures to create realistic CT tumor phantoms with the desired range of radiodensities. The 3D printed tumor phantoms also precisely replicated real lung tumor patient data regarding morphology and could also include life-like heterogeneity of the radiodensity inside the tumor models. An influence of the heterogeneity on accuracy and robustness of the image registration algorithms was not found.

X-ray attenuation of bone, soft and adipose tissue in CT from 70 to 140 kV and comparison with 3D printable additive manufacturing materials.

Additive manufacturing and 3D printing are widely used in medical imaging to produce phantoms for image quality optimization, imaging protocol definition, comparison of image quality between different imaging systems, dosimetry, and quality control. Anthropomorphic phantoms mimic tissues and contrasts in real patients with regard to X-ray attenuation, as well as dependence on X-ray spectra. If used with different X-ray energies, or to optimize the spectrum for a certain procedure, the energy dependence of the attenuation must replicate the corresponding energy dependence of the tissues mimicked, or at least be similar. In the latter case the materials' Hounsfield values need to be known exactly to allow to correct contrast and contrast to noise ratios accordingly for different beam energies. Fresh bovine and porcine tissues including soft and adipose tissues, and hard tissues from soft spongious bone to cortical bone were scanned at different energies, and reference values of attenuation in Hounsfield units (HU) determined. Mathematical model equations describing CT number dependence on kV for bones of arbitrary density, and for adipose tissues are derived. These data can be used to select appropriate phantom constituents, compare CT values with arbitrary phantom materials, and calculate correction factors for phantoms consisting of materials with an energy dependence different to the tissues. Using data on a wide number of additive manufacturing and 3D printing materials, CT numbers and their energy dependence were compared to those of the tissues. Two commercially available printing filaments containing calcium carbonate powder imitate bone tissues with high accuracy at all kV values. Average adipose tissue can be duplicated by several off-the-shelf printing polymers. Since suitable printing materials typically exhibit a too high density for the desired attenuation of especially soft tissues, controlled density reduction by underfilling might improve tissue equivalence.

Technical note: A PET/MR coil with an integrated, orbiting 511 keV transmission source for PET/MR imaging validated in an animal study.

BACKGROUND: MR-based methods for attenuation correction (AC) in PET/MRI either neglect attenuation of bone, or use MR-signal derived information about bone, which leads to a bias in quantification of tracer uptake in PET. In a previous study, we presented a PET/MRI specific MR coil with an integrated transmission source (TX) system allowing for direct measurement of attenuation. In phantom measurements, this system successfully reproduced the linear attenuation coefficient of water. PURPOSE: The purpose of this study is to validate the TX system in a clinical setting using animals and to show its applicability compared to standard clinical methods. METHODS: As test subject, a 15-kg piglet was injected with 53 MBq of 18F-NaF. The µ-map obtained with the TX system and the reconstructed activity distribution were compared to four established AC methods: a Dixon sequence, an ultra-short echo time (UTE) sequence, a CT scan, and a 511 keV transmission scan using a Siemens ECAT EXACT HR+ as the reference. The PET/MRI measurements were performed on a Siemens Biograph mMR to obtain the µ-map using the TX system as well as the Dixon and UTE sequence directly followed by the CT and ECAT measurements. RESULTS: The reconstructed activity distribution using the TX system for AC showed similar results compared to the reference (<5% difference in hot regions) and outperformed the MR-based methods as implemented in the PET/MRI system (<10% difference in hot regions). However, the additional hardware of the TX system adds complexity to the acquisition process. CONCLUSION: Our porcine study demonstrates the feasibility of post-injection transmission scans using the developed TX system in a clinical setting. This makes it a useful tool for PET/MRI in cases where transmission information is needed for AC. Potential applications are studies using larger animals where state-of-the-art atlas-based or artificial intelligence AC methods are not available.

3D ultrasound guided navigation system with hybrid image fusion.

A prototype of a navigation system to fuse two image modalities is presented. The standard inter-modality registration is replaced with a tracker-based image registration of calibrated imaging devices. Intra-procedure transrectal US (TRUS) images were merged with pre-procedure magnetic resonance (MR) images for prostate biopsy. The registration between MR and TRUS images was performed by an additional abdominal 3D-US (ab-3D-US), which enables replacing the inter-modal MR/TRUS registration by an intra-modal ab-3D-US/3D-TRUS registration. Calibration procedures were carried out using an optical tracking system (OTS) for the pre-procedure image fusion of the ab-3D-US with the MR. Inter-modal ab-3D-US/MR image fusion was evaluated using a multi-cone phantom for the target registration error (TRE) and a prostate phantom for the Dice score and the Hausdorff distance of lesions . Finally, the pre-procedure ab- 3D-US was registered with the TRUS images and the errors for the transformation from the MR to the TRUS were determined. The TRE of the ab-3D-US/MR image registration was 1.81 mm. The Dice-score and the Hausdorff distance for ab-3D-US and MR were found to be 0.67 and 3.19 mm. The Dice score and the Hausdorff distance for TRUS and MR were 0.67 and 3.18 mm. The hybrid navigation system showed sufficient accuracy for fusion guided biopsy procedures with prostate phantoms. The system might provide intra-procedure fusion for most US-guided biopsy and ablation interventions.

Toward on-the-fly trajectory optimization for C-arm CBCT under strong kinematic constraints.

Cone beam computed tomography (CBCT) has become a vital tool in interventional radiology. Usually, a circular source-detector trajectory is used to acquire a three-dimensional (3D) image. Kinematic constraints due to the patient size or additional medical equipment often cause collisions with the imager while performing a full circular rotation. In a previous study, we developed a framework to design collision-free, patient-specific trajectories for the cases in which circular CBCT is not feasible. Our proposed trajectories included enough information to appropriately reconstruct a particular volume of interest (VOI), but the constraints had to be defined before the intervention. As most collisions are unpredictable, performing an on-the-fly trajectory optimization is desirable. In this study, we propose a search strategy that explores a set of trajectories that cover the whole collision-free area and subsequently performs a search locally in the areas with the highest image quality. Selecting the best trajectories is performed using simulations on a prior diagnostic CT volume which serves as a digital phantom for simulations. In our simulations, the Feature SIMilarity Index (FSIM) is used as the objective function to evaluate the imaging quality provided by different trajectories. We investigated the performance of our methods using three different anatomical targets inside the Alderson-Rando phantom. We used FSIM and Universal Quality Image (UQI) to evaluate the final reconstruction results. Our experiments showed that our proposed trajectories could achieve a comparable image quality in the VOI compared to the standard C-arm circular CBCT. We achieved a relative deviation less than 10% for both FSIM and UQI metrics between the reconstructed images from the optimized trajectories and the standard C-arm CBCT for all three targets. The whole trajectory optimization took approximately three to four minutes.

Optimization for customized trajectories in cone beam computed tomography.

PURPOSE: We developed a target-based cone beam computed tomography (CBCT) imaging framework for optimizing an unconstrained three dimensional (3D) source-detector trajectory by incorporating prior image information. Our main aim is to enable a CBCT system to provide topical information about the target using a limited angle noncircular scan orbit with a minimal number of projections. Such a customized trajectory should include enough information to sufficiently reconstruct a particular volume of interest (VOI) under kinematic constraints, which may result from the patient size or additional surgical or radiation therapy-related equipment. METHODS: A patient-specific model from a prior diagnostic computed tomography (CT) volume is used as a digital phantom for CBCT trajectory simulations. Selection of the best projection views is accomplished through maximizing an objective function fed by the imaging quality provided by different x-ray positions on the digital phantom data. The final optimized trajectory includes a limited angular range and a minimal number of projections which can be applied to a C-arm device capable of general source-detector positioning. The performance of the proposed framework is investigated in experiments involving an in-house-built box phantom including spherical targets as well as an Alderson-Rando head phantom. In order to quantify the image quality of the reconstructed image, we use the average full-width-half-maximum (FWHMavg ) for the spherical target and feature similarity index (FSIM), universal quality index (UQI), and contrast-to-noise ratio (CNR) for an anatomical target. RESULTS: Our experiments based on both the box and head phantom showed that optimized trajectories could achieve a comparable image quality in the VOI with respect to the standard C-arm circular CBCT while using approximately one quarter of projections. We achieved a relative deviation <7% for FWHMavg between the reconstructed images from the optimized trajectories and the standard C-arm CBCT for all spherical targets. Furthermore, for the anatomical target, the relative deviation of FSIM, UQI, and CNR between the reconstructed image related to the proposed trajectory and the standard C-arm circular CBCT was found to be 5.06%, 6.89%, and 8.64%, respectively. We also compared our proposed trajectories to circular trajectories with equivalent angular sampling as the optimized trajectories. Our results show that optimized trajectories can outperform simple partial circular trajectories in the VOI in term of image quality. Typically, an angular range between 116° and 152° was used for the optimized trajectories. CONCLUSION: We demonstrated that applying limited angle noncircular trajectories with optimized orientations in 3D space can provide a suitable image quality for particular image targets and has a potential for limited angle and low-dose CBCT-based interventions under strong spatial constraints.

Additively Manufactured Patient-Specific Anthropomorphic Thorax Phantom With Realistic Radiation Attenuation Properties.

Conventional medical imaging phantoms are limited by simplified geometry and radiographic skeletal homogeneity, which confines their usability for image quality assessment and radiation dosimetry. These challenges can be addressed by additive manufacturing technology, colloquially called 3D printing, which provides accurate anatomical replication and flexibility in material manipulation. In this study, we used Computed Tomography (CT)-based modified PolyJetTM 3D printing technology to print a hollow thorax phantom simulating skeletal morphology of the patient. To achieve realistic heterogenous skeletal radiation attenuation, we developed a novel radiopaque amalgamate constituting of epoxy, polypropylene and bone meal powder in twelve different ratios. We performed CT analysis for quantification of material radiodensity (in Hounsfield Units, HU) and for identification of specific compositions corresponding to the various skeletal structures in the thorax. We filled the skeletal structures with their respective radiopaque amalgamates. The phantom and isolated 3D printed rib specimens were rescanned by CT for reproducibility tests regarding verification of radiodensity and geometry. Our results showed that structural densities in the range of 42-705HU could be achieved. The radiodensity of the reconstructed phantom was comparable to the three skeletal structures investigated in a real patient thorax CT: ribs, ventral vertebral body and dorsal vertebral body. Reproducibility tests based on physical dimensional comparison between the patient and phantom CT-based segmentation displayed 97% of overlap in the range of 0.00-4.57 mm embracing the anatomical accuracy. Thus, the additively manufactured anthropomorphic thorax phantom opens new vistas for imaging- and radiation-based patient care in precision medicine.

Evaluation of 3D ultrasound for image guidance.

PURPOSE: In this paper we compared two different 3D ultrasound (US) modes (3D free-hand mode and 3D wobbler mode) to see which is more suitable to perform the 3D-US/3D-US registration for clinical guidance applications. The typical errors with respect to their impact on the final localization error were evaluated step by step. METHODS: Multi-point target and Hand-eye calibration methods were used for 3D US calibration together with a newly designed multi-cone phantom. Pointer based and image based methods were used for 2D US calibration. The calibration target error was computed by using a different multi-cone phantom. An egg-shaped phantom was used as ground truth to compare distortions for both 3D modes along with the measurements of the volume. Finally, we compared 3D ultrasound images acquired by 3D wobbler mode and 3D free-hand mode with respect to their 3D-US/3D-US registration accuracy using both, phantom and patient data. A theoretical step by step error analysis was performed and compared to empirical data. RESULTS: Target registration errors based on the calibration with the 3D Multi-point and 2D pointer/image method have been found to be comparable (∼1mm). They both outperformed the 3D Hand-eye method (error >2mm). Volume measurements with the 3D free-hand mode were closest to the ground truth (around 6% error compared to 9% with the 3D wobbler mode). Additional scans on phantoms showed a 3D-US/3D-US registration error below 1 mm for both, the 3D free-hand mode and the 3D wobbler mode, respectively. Results with patient data showed greater error with the 3D free-hand mode (6.50mm - 13.37mm) than with the 3D wobbler mode (2.99 ± 1.54 mm). All the measured errors were found to be in accordance to their theoretical upper bounds. CONCLUSION: While both 3D volume methods showed comparable results with respect to 3D-US/3D-US registration for phantom images, for patient data registrations the 3D wobbler mode is superior to the 3D free-hand mode. The effect of all error sources could be estimated by theoretical derivations.

Midfacial Advancement Line-A Comparative Evaluation of a New Measurement Method in Orthognathic Surgery.

PURPOSE: In planning intraoral quadrangular Le Fort II osteotomy (IQLFIIO), simulation of hard and soft tissue changes will be important at the infraorbital, Le Fort I, and incisor level. The aim of our study was to evaluate a new method for visualization and quantification. MATERIALS AND METHODS: Three different methods of quantification were compared: the point-to-point (PTP) measurement, which has been viewed as the reference standard; part comparison analysis (PCA); and a new method, the midfacial advancement line (MFAL) measurement. We performed a measurement comparison study using the Bland-Altman method to measure agreement and enrolled patients with midfacial deficiency and Class III malocclusion who had undergone IQLFIIO. The primary predictor variable was the method of measurement. The primary outcome variable was the amount of midfacial advancement. We also investigated the time required, visualization quality, and interobserver agreement. RESULTS: The sample included 12 subjects with a mean age of 21.6 years; 7 patients were male. The PTP and MFAL showed no significant observer dependence. The advancement measured with PTP and MFAL showed no significant differences. However, the advancement measured using MFAL and PCA showed a significant difference. The highest rating of visualization was found for MFAL. The time requirements were similar for all 3 methods. CONCLUSIONS: Our results have shown that the MFAL is a suitable method for visualization and quantification of soft and hard tissue changes at all 3 face levels in 1 image. It could be a valuable tool for virtual planning of midfacial advancement surgery.

Design, Implementation, and Evaluation of a Head and Neck MRI RF Array Integrated with a 511 keV Transmission Source for Attenuation Correction in PET/MR.

The goal of this work is to further improve positron emission tomography (PET) attenuation correction and magnetic resonance (MR) sensitivity for head and neck applications of PET/MR. A dedicated 24-channel receive-only array, fully-integrated with a hydraulic system to move a transmission source helically around the patient and radiofrequency (RF) coil array, is designed, implemented, and evaluated. The device enables the calculation of attenuation coefficients from PET measurements at 511 keV including the RF coil and the particular patient. The RF coil design is PET-optimized by minimizing photon attenuation from coil components and housing. The functionality of the presented device is successfully demonstrated by calculating the attenuation map of a water bottle based on PET transmission measurements; results are in excellent agreement with reference values. It is shown that the device itself has marginal influence on the static magnetic field B0 and the radiofrequency transmit field B1 of the 3T PET/MR system. Furthermore, the developed RF array is shown to outperform a standard commercial 16-channel head and neck coil in terms of signal-to-noise ratio (SNR) and parallel imaging performance. In conclusion, the presented hardware enables accurate calculation of attenuation maps for PET/MR systems while improving the SNR of corresponding MR images in a single device without degrading the B0 and B1 homogeneity of the scanner.

Comparison of a personalized breast dosimetry method with standard dosimetry protocols.

Average glandular dose (AGD) in digital mammography crucially depends on the estimation of breast glandularity. In this study we compared three different methods of estimating glandularities according to Wu, Dance and Volpara with respect to resulting AGDs. Exposure data from 3050 patient images, acquired with a GE Senographe Essential constituted the study population of this work. We compared AGD (1) according to Dance et al. applying custom g, c, and s factors using HVL, breast thickness, patient age and incident air kerma (IAK) from the DICOM headers; (2) according to Wu et al. as determined by the GE system; and (3) AGD derived with the Dance model with personalized c factors using glandularity determined with the Volpara (Volpara Solutions, Wellington, New Zealand) software (Volpare AGD). The ratios of the resulting AGDs were analysed versus parameters influencing dose. The highest deviation between the resulting AGDs was found in the ratio of GE AGD to Volpara AGD for breast thicknesses between 20 and 40 mm (ratio: 0.80). For thicker breasts this ratio is close to one (1 ± 0.02 for breast thicknesses >60 mm). The Dance to Volpara ratio was between 0.86 (breast thickness 20-40 mm) and 0.99 (>80 mm), and Dance/GE AGD was between 1.07 (breast thickness 20-40 mm) and 0.98 (41-60, and >80 mm). Glandularities by Volpara were generally smaller than the one calculated with the Dance method. This effect is most pronounced for small breast thickness and older ages. Taking the considerable divergences between the AGDs from different methods into account, the selection of the method should by done carefully. As the Volpara method provides an analysis of the individual breast tissue, while the Wu and the Dance methods use look up tables and custom parameter sets, the Volpara method might be more appropriate if individual ADG values are sought. For regulatory purposes and comparison with diagnostic reference values, the method to be used needs to be defined exactly and clearly be stated. However, it should be accepted that dose values calculated with standardized models, like AGD and also effective dose, are afflicted with a considerable uncertainty budgets that need to be accounted for in the interpretation of these values.

Deformable registration of 3D ultrasound volumes using automatic landmark generation.

US image registration is an important task e.g. in Computer Aided Surgery. Due to tissue deformation occurring between pre-operative and interventional images often deformable registration is necessary. We present a registration method focused on surface structures (i.e. saliencies) of soft tissues like organ capsules or vessels. The main concept follows the idea of representative landmarks (so called leading points). These landmarks represent saliencies in each image in a certain region of interest. The determination of deformation was based on a geometric model assuming that saliencies could locally be described by planes. These planes were calculated from the landmarks using two dimensional linear regression. Once corresponding regions in both images were found, a displacement vector field representing the local deformation was computed. Finally, the deformed image was warped to match the pre-operative image. For error calculation we used a phantom representing the urinary bladder and the prostate. The phantom could be deformed to mimic tissue deformation. Error calculation was done using corresponding landmarks in both images. The resulting target registration error of this procedure amounted to 1.63 mm. With respect to patient data a full deformable registration was performed on two 3D-US images of the abdomen. The resulting mean distance error was 2.10 ± 0.66 mm compared to an error of 2.75 ± 0.57 mm from a simple rigid registration. A two-sided paired t-test showed a p-value < 0.001. We conclude that the method improves the results of the rigid registration considerably. Provided an appropriate choice of the filter there are many possible fields of applications.

Equivalent thicknesses of beam hardening filters consisting of aluminium, copper, Al/Cu and Al/Gold combinations and plumbiferous acrylic for 40 to 150 kVp diagnostic spectra.

PURPOSE: Beam hardening filters used to reduce patient doses typically consist of aluminium, copper, or a combination of both. Optically transparent filters containing lead in plumbiferous acrylic became available. One vendor also uses a combination of aluminium and gold. Data is provided to compare filter thicknesses in terms of half-value layer (HVL) for clinically relevant kVp. METHODS: Equivalent filter thicknesses were defined by identical kVp and 1st HVL. Equivalent copper filter thicknesses were calculated for aluminium and typical filters found in radiographic and interventional systems. A verified semi-empirical spectrum calculation programme and National Institute of Standards and Technology (NIST) mass attenuation coefficients were applied. Lead acrylic filters were simulated by a two-component model of acrylic plus lead with mass thicknesses determined by matching 1 HVLs in Al at RQR5 using filter specifications. RESULTS: Coefficients are provided to convert mm Cu to mm Al and vice versa for tube potentials from 40 to 150 kVp. 1 mm Al corresponds to 27.8 ± 1 µm Cu over the entire energy range simulated. Using this simple model as opposed to simulations of all individual filters made from Al/Cu combinations (1 and 2 mm Al, 1 Al + 0.1 and 0.2 Cu, 1.5 Al plus 0.3 and 0.6 Cu, 2 Al plus 0.1 Cu) for the entire energy range results in differences in equivalent Cu thicknesses below 4 µm Cu (3 µm for 50-150 kVp). kVp dependence is larger for filters containing larger Z elements. 1 mm Al plus 10 µm gold used by Shimadzu corresponds to 75-80 µm Cu, depending on kVp; plumbiferous acrylic with nominal filtrations of 1 Al plus 0.1 Cu, and 1 Al plus 0.2 Cu corresponded to 124-132 µm, and 206-232 µm Cu, respectively. CONCLUSIONS: Experimental verification of the equivalence of aluminium and combined aluminium plus copper filters showed excellent agreement between calculated copper equivalent thickness and measurements with copper filters for clinical beams from 40 to 150 kVp.

Soft Tissue Changes in Patients Undergoing Intraoral Quadrangular Le Fort II Osteotomy Versus Conventional Le Fort I Osteotomy.

PURPOSE: The aim of this study was to evaluate soft tissue changes after intraoral quadrangular Le Fort II osteotomy (IOQLFII) and correlate those changes to underlying osseous changes. MATERIALS AND METHODS: Twenty-six non-growing patients with midfacial deficiency and Class III malocclusion were analyzed. A study group of 13 patients who underwent IOQLFII was compared with 13 patients who underwent conventional Le Fort I osteotomy (LFI). After fusion of pre- and postoperative computed tomograms, each patient's hard and corresponding soft tissue changes were measured. Measurement points were defined at 3 levels in the IOQLFII group (infraorbital rim [IR], sinus floor [SF], and lateral incisor tip [LI]) and at 2 levels in the LFI group (SF and LI). Linear models were created to test for correlations between hard and soft tissues. RESULTS: The slope (a1 coefficient) between anteroposterior hard and soft tissue changes was found to be highly significant at each measurement point for all groups. In the IOQLFII group, soft tissue advancement was 69% (confidence interval [CI], 62 to 77%) of the hard tissue advancement at the IR, 90% (CI, 84 to 96%) at the SF, and 73% (CI, 64 to 82%) at the LI. In the LFI group, the corresponding percentages were 90% (83 to 97%) at SF and 84% (77 to 90%) at LI. CONCLUSION: IOQLFII results in predictable correction of midfacial deficiency. At the IR, bony advancement always resulted in markedly less soft tissue advancement than at the SF level. These results indicate that the planned infraorbital advancement should not be too conservative because soft tissue changes are smaller in this region.

Design of a head phantom produced on a 3D rapid prototyping printer and comparison with a RANDO and 3M lucite head phantom in eye dosimetry applications.

An anthropomorphic head phantom including eye inserts allowing placement of TLDs 3 mm below the cornea has been produced on a 3D printer using a photo-cured acrylic resin to best allow tissue equivalence. Thus Hp(3) can be determined in radiological and interventional photon radiation fields. Eye doses and doses to the forehead have been compared to an Alderson RANDO head and a 3M Lucite skull phantom in terms of surface dose per incident air kerma for frontal irradiation since the commercial phantoms do not allow placement of TLDs 3 mm below the corneal surface. A comparison of dose reduction factors (DRFs) of a common lead glasses model has also been performed. Eye dose per incident air kerma were comparable between all three phantoms (printed phantom: 1.40, standard error (SE) 0.04; RANDO: 1.36, SE 0.03; 3M: 1.37, SE 0.03). Doses to the forehead were identical to eye surface doses for the printed phantom and the RANDO head (ratio 1.00 SE 0.04, and 0.99 SE 0.03, respectively). In the 3M Lucite skull phantom dose on the forehead was 15% lower than dose to the eyes attributable to phantom properties. DRF of a sport frame style leaded glasses model with 0.75 mm lead equivalence measured were 6.8 SE 0.5, 9.3 SE 0.4 and 10.5 SE 0.5 for the RANDO head, the printed phantom, and the 3M Lucite head phantom, respectively, for frontal irradiation. A comparison of doses measured in 3 mm depth and on the surface of the eyes in the printed phantom revealed no difference larger than standard errors from TLD dosimetry. 3D printing offers an interesting opportunity for phantom design with increasing potential as printers allowing combinations of tissue substitutes will become available. Variations between phantoms may provide a useful indication of uncertainty budgets when using phantom measurements to estimate individual personnel doses.

Technical Note: Fully-automated analysis of Jaszczak phantom measurements as part of routine SPECT quality control.

PURPOSE: Inspection and quantitative validation of tomographic imaging properties of SPECT systems, i.e., spatial resolution, contrast, and inhomogeneity must be performed in regular intervals. Typically, the modular Jaszczak phantom is used for that purpose, as it offers the possibility to investigate all three system properties with a single measurement. The interpretation of the measurement is performed visually, thus, being insensitive to subtle changes in system performance. To overcome this limitation, a fully-automated software for the objective analysis of Jaszczak phantom measurements is proposed here. METHODS: The software was developed as an ImageJ plugin and offers a number of sequential evaluation steps: automatic determination of the type of Jaszczak phantom, calculation of sector and sphere contrast, detection of ring artifacts using either the Hough transform, followed by a threshold-based decision criterion, or Student's t-test. Monte Carlo simulations were used to estimate the detectability limits for ring artifacts. RESULTS: The software successfully calculated sector and sphere contrasts and reliably determined ring artifacts present in the homogeneity part of the Jaszczak phantom, based on automatic identification of the phantom type. CONCLUSION: Given the quantitative nature of the produced output, results from one imaging system can easily be compared to another in an objective way. The advantage of the software is clearly that the information provided is objective and does not rely on the experience level of the user.

Conversion factors between human and automatic readouts of CDMAM phantom images of CR mammography systems.

In mammography screening, profound assessment of technical image quality is imperative. The European protocol for the quality control of the physical and technical aspects of mammography screening (EPQCM) suggests using an alternate fixed choice contrast-detail phantom-like CDMAM. For the evaluation of technical image quality, human or automated readouts can be used. For automatic evaluation, a software (cdcom) is provided by EUREF. If the automated readout indicates unacceptable image quality, additional human readout may be performed overriding the automated readout. As the latter systematically results in higher image quality ratings, conversion factors between both methods are regularly applied. Since most image quality issues with mammography systems arise within CR systems, an assessment restricted to CR systems with data from the Austrian Reference Center in the mammography screening program has been conducted. Forty-five CR systems were evaluated. Human readouts were performed with a randomisation software to avoid bias due to learning effects. Additional automatic evaluation allowed for the computation of conversion factors between human and automatic readouts. These factors were substantially lower compared to those suggested by EUREF, namely 1.21 compared to 1.62 (EUREF UK method) and 1.42 (EUREF EU method) for 0.1 mm, and 1.40 compared to 1.83 (EUREF UK) and 1.73 (EUREF EU) for 0.25 mm structure size, respectively. Using either of these factors to adjust patient dose in order to comply with image quality requirements results in differences in the dose increase of up to 90%. This necessitates a consensus on their proper application and limits the validity of the assessment methods. Clear criteria for CR systems based on appropriate studies should be promoted.

Spectrum optimization for computed radiography mammography systems.

PURPOSE: Technical quality assurance is a key issue in breast screening protocols. While full-field digital mammography systems produce excellent image quality at low dose, it appears difficult with computed radiography (CR) systems to fulfill the requirements for image quality, and to keep the dose below the limits. However, powder plate CR systems are still widely used, e.g., they represent ∼30% of the devices in the Austrian breast cancer screening program. For these systems the selection of an optimal spectrum is a key issue. METHODS: We investigated different anode/filter (A/F) combinations over the clinical range of tube voltages. The figure-of-merit (FOM) to be optimized was squared signal-difference-to-noise ratio divided by glandular dose. Measurements were performed on a Siemens Mammomat 3000 with a Fuji Profect reader (SiFu) and on a GE Senograph DMR with a Carestream reader (GECa). RESULTS: For 50mm PMMA the maximum FOM was found with a Mo/Rh spectrum between 27kVp and 29kVp, while with 60mm Mo/Rh at 28kVp (GECa) and W/Rh 25kVp (SiFu) were superior. For 70mm PMMA the Rh/Rh spectrum had a peak at about 31kVp (GECa). FOM increases from 10% to >100% are demonstrated. CONCLUSION: Optimization as proposed in this paper can either lead to dose reduction with comparable image quality or image quality improvement if necessary. For systems with limited A/F combinations the choice of tube voltage is of considerable importance. In this work, optimization of AEC parameters such as anode-filter combination and tube potential was demonstrated for mammographic CR systems.