Repeatable and standardized quantitative assessment of diagnostic image quality in contrast-enhanced mammography (CEM) is limited by the absence of realistic pseudo-anthropomorphic phantoms. We extended the L2 phantom mimicking realistic anatomical noise by integrating a plate containing 3D-printed iodine inserts of varying areal densities and diameters, enabling systematic evaluation of iodine detectability with a structured background. A key feature of the L2 phantom is the possibility to generate different background patterns by agitating the phantom. CEM images were acquired on a Siemens Mammomat Revelation system at 28 kV in TiCEM dual-energy mode with automatic exposure control. 8 readers participated in a Four-Alternative Forced Choice (4AFC) study with 12 independent acquisitions per condition, each performed after gentle phantom agitation to generate unique background configurations. Psychometric functions were fitted for each reader to determine detection thresholds set at 62.5% correct readings as a function of both cylinder diameter and iodine concentration. Detectability improved with increasing iodine content and cylinder size. Intra- and inter-reader variability decreased with higher signal conspicuity, and geometric distortion was negligible ([Formula: see text]). As a proof-of-concept study, the thresholds determined provide quantitative benchmarks for phantom-based comparison of CEM acquisition protocols and technical performance assessment on the investigated system. Overall, the L2 phantom with the added iodine contrast detail plate, combined with the 4AFC framework, offers a promising tool for evaluating image quality and assessing iodine detectability in CEM under controlled phantom conditions.

Background: L2 represents a breast phantom with structured non-static background. By shaking the phantom between the image acquisitions a different background configuration is achieved. In this work, the variability of the background of multiple models of the phantom is assessed. Methods: Four models of the phantom where manufactured. 60 2D image acquisitions of one model and each 12 2D image acquisitions of the three further models where perfomed at automatic exposure control (AEC) dose level. Regions of interest where defined in the non-static background of the phantom models followed by radiomic feature extraction using the open-source software Lifex (www.lifexsoft.org). Results: From 110 extracted radiomic features 16 were found to be high reproducible within 60 image acquisitions of one model and each 12 images of three further models of the L2 phantom. Conclusion: The reproducibility of the manufacturing process of a 3D structured breast phantom was investigated by extracting radiomic features. The variability within four models of the phantom was found to be within the range of the variability of 60 image acquisitions of one model. With regard to extracted features, the manufacturing process of the non-static background is reproducible.

Objective To test whether a locally hosted, retrieval-augmented clinical decision framework (CDF) improves recognition of cocaine-induced midline destructive lesions (CIMDL)—a malignancy mimicker—during dental teleconsultation, compared with a cloud large language model (LLM) without retrieval. Materials and Methods We conducted a paired feasibility evaluation using 401 simulated consultations derived from Sigmund Freud’s historical lesion narrative. The local CDF used mistral-7b-instruct-v0.2 with retrieval-augmented generation (RAG) over a curated CIMDL corpus; the comparator was GPT-4o accessed without retrieval. Identical prompts and clinical context were used in both arms. The primary endpoint was inclusion of CIMDL in the differential diagnosis, adjudicated against published criteria. Paired outcomes were compared with McNemar’s test; odds ratios (OR) and 95% confidence intervals (CI) were computed from discordant pairs. Results On the MAIN-prompt dataset, the local RAG model identified CIMDL more often than the cloud comparator (discordant pairs: 44 [local-only] vs 19 [cloud-only]; χ2 with Yates correction = 9.14, p = 0.0025; OR = 2.28, 95% CI 1.34–3.89). Conclusions Under realistic privacy constraints, a RAG-enabled local framework improved recognition of a key cancer mimicker during dental triage relative to a cloud LLM without retrieval. Clinical Relevance Enhanced early recognition of CIMDL may prevent misclassification as oral SCC and expedite appropriate referral; local, privacy-preserving AI is feasible for chairside decision support.

IntroductionThe image formation process of conventional pulse-echo Ultrasound mainly uses the backscattered amplitude and assumes constant attenuation and speed of sound in the penetrated media. Thus, many commercially available ultrasound imaging phantoms use only a limited choice of materials with simple geometric shapes. Part of today’s research in ultrasound is to gain more information on the acoustic properties of the object imaged. These advanced imaging and reconstruction procedures require more complicated phantom designs that contain different materials with precisely designable acoustic properties for validation and quality assurance (QA).MethodsTo fabricate such phantoms, we produced molds for casting ultrasound phantoms using additive manufacturing. Phantom materials used were based on agar and polyvinyl alcohol. To adapt the speed of sound glycerol was added to the mixtures. As glycerol diffuses out of the phantom material, polluting the surrounding water, we designed a watertight sample holder. The effect of the freeze-thaw cycles (FTCs) on the acoustic properties of the polyvinyl alcohol (PVA)-based phantoms was also investigated. Speed of sound and attenuation were determined for both phantoms materials, and Shore hardness measured for the PVA-based phantoms.ResultsShore hardness of the PVA phantoms increased by up to 79% of the initial value with increasing number of freeze-thaw cycles, but showed a saturation after 5 FTCs. However, the number of FTCs had only a small effect on the speed of sound and attenuation, as the sound speed increased slightly from 1,530.14 m/s to 1,558.53 m/s, (1.86%) and the attenuation exhibited only an increase of 6.75%. In contrast, differences of around 100 m/s in the speed of sound in the PVA phantoms (from 1,558.53 to 1,662.27 m/s), as well as in the agar-based phantoms (from 1,501.74 to 1,609.36 m/s) could be achieved by adding glycerol, making these materials appropriate candidates for the design and fabrication of US phantoms with defined sections and details with different speed of sound and attenuation. The use of the sample holder showed only an influence of 0.63% on the measured speed of sound.Discussion3D printed molds led to an improved manufacturing process as well as a free choice of the shape of the phantoms. A sample holder could prevent contamination of the water with no significant differences in the measured speed of sound.

The assessment of clinical image quality on ultrasound is currently often subjective. While image quality factors such as contrast response or depth of penetration can be evaluated semi-automatically, the evaluation of high contrast resolution requires test objects with specific inserts. The aim of this study was to evaluate the applicability of image quality metrics which were derived from Linear System Theory in the field of medical ultrasound imaging. Modular Transfer Function (MTF) and noise power spectrum (NPS) were determined on four phantoms. Image quality was assessed using a detectability index for different diameters. One phantom contained a cylinder filled with water, which appears as a circle in the US images. The other three phantoms were homogeneous and consisted of three different materials all based on PVA (polyvinyl alcohol). The basic phantom material was a 10% PVA hydrogel. The two other materials included microplastic spheres and starch to increase echogeneity. NPS and the MTF were determined using MATLAB routines. Two linear US transducers with bandwidths of 2.4–10 and 4–15 MHz were used to show the dependence of the index on the principal frequency of the US wave. The results show that for all phantom materials and object sizes (1–10 mm diameter), the detectability indices decreased with increasing penetration depth (from 6 to 10 cm). In addition, all indices of the higher frequency transducer were higher than those of the lower frequency transducer. When comparing the different phantom materials (PVA, PVA with starch and PVA with microspheres), different mean pixel value (MPV) were found, while the standard deviations for the materials were similar. This enabled us to evaluate the detectability index at different signal-to-noise ratios (SNR). Measures of image homogeneity (coefficient of the variance and variation) showed no significant difference to a commercial phantom (p-values ranging from 0.16 to 1, average p-value 0.5). These results suggest that the concept of a detectability index can also be applied to US imaging.

Ultrasound imaging can be used to visualize the boundaries between two media with different properties, but less information is available about the medium penetrated. Therefore, conventional ultrasound devices used in routine medical imaging usually assume a constant value for the speed of sound of the structures. Thus, current research aims to develop new methods to obtain more information about the medium scanned. To support the research ultrasound phantoms with precisely known properties like speed of sound, attenuation or hardness can be used. We developed polyvinyl alcohol based phantoms and investigated the correlation between the properties and the freeze-thaw cycles (FTC), as well as the effects of glycerol on the speed of sound. Additionally, we designed 3D printed molds for shaping the phantom and improving the FTC process. Furthermore, a construction was designed to prevent the measurement setup from being contaminated by PVA and glycerol defusing out of the phantom. The physical properties of the phantoms measured were the speed of sound, attenuation and Shore hardness. The measurements conducted were carried out using the standards of the American Institute for Ultrasound in Medicine (AIUM) and the American Society for Testing and Materials (ASTM). There was an increase in Shore hardness and speed of sound as the number of FTCs increased. However, the differences in the speed of sound were only minimal, whereby higher differences could be achieved by the addition of glycerol. At present, no statements can be made about the attenuation. The measurements of the materials are in an early state and further improvement is needed. The manufacturing process and measurements were improved by 3D printed molds.

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.

The goal of this study was the development of a phantom for the determination of the image quality of ultrasound (US) based on the Linear System Theory. Modular transfer Function (MTF) and noise power spectrum (NPS) were determined on two US phantoms. One contained a cylinder filled with water, which appears as a circle in the US images, the second was completely homogeneous. The base material of the phantom was Poly(vinyl alcohol) which was mixed with water in a 1:9 ratio. Additionally, micro-plastic spheres and starch, respectively, were included to increase echogenicity. An algorithm was developed that calculates a radial MTF from the circular structure representing spatial resolution averaged across all directions. Noise power spectrum was determined as described by Fredenberg et al., image quality was evaluated by means of a detectability index for different diameters. Two transducers with different bandwidths (4-13 MHz and 3-8 MHz) were used to show the dependence of the index on the main frequency of the US wave. In addition, three penetration depths, which also require different frequencies, were used. Detectability was higher with the transducer of higher frequency for all measurements i.e. for all depths and all diameters (paired t-tests, all p < 0.01). There was also a decrease of detectability with increasing depth for both transducers. The dependence of the index on the axial distance of the ROIs was highly significant (two-sided, paired Wilcoxon test, p < 0.00001). With respect to the comparison for the different phantom materials (PVA with starch and PVA with micro-spheres), the null hypothesis (equality of variances; unpaired, two-sided Wilcoxon test) could not be rejected (p = 0.14). The results suggest that the concept of the detectability index can also be applied to US images with some reservations.

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.

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.

AbstractBackgroundMR‐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.PurposeThe 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.MethodsAs 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.ResultsThe 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.ConclusionOur 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.

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.

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.

•It is possible to better photobiomodulation therapy in the fields of oral and maxillofacial surgery by optimizing dosage.•Photobiomodulation therapy enhances regeneration in the maxillofacial region.•Photobiomodulation improves implant osseointegration in the maxillofacial region.

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.

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 PolyJet(TM) 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.

Purpose In this work we present equivalent breast thickness and dose sensitivity of a next iteration 3D structured breast phantom with lesion models to demonstrate its potential use for quality assurance measurements in breast imaging. Methods PMMA equivalent thickness was determined employing the automatic exposure control (AEC) of Siemens Mammomat Inspiration and Siemens Mammomat Revelation. A 2D projection image of the phantom was acquired and the corresponding AEC settings recorded as reference. Equivalent PMMA thickness was found by interpolating between three PMMA thicknesses with mAs values close to the reference settings selected by AEC. Dose sensitivity of the reconstructed digital breast tomosynthesis (DBT) images was assessed by two experienced readers using a four alternative forced choice (4-AFC) study. Three different dose levels for lesion models and microcalcifications were evaluated. Results PMMA equivalent thickness of the phantom was 46.8 mm and 47.0 mm for measurements on Siemens Mammomat Inspiration and Siemens Mammomat Revelation which equals to a breast equivalent thickness of 55.5 mm and 55.8 mm, respectively, compared to a physical phantom thickness of 53.5 mm. For lesion models dose sensitiviy of the detectability was not obvious. For microcalcification the diameter threshold was found to increase for decreasing dose from high dose to AEC to low dose. Conclusions We found the measured equivalent breast thickness of our phantom to be close to its physical thickness. It can be concluded that changes in dose can be detected by the presented phantom for the tested dose levels.

Purpose We present a systematic error analysis for a navigation system which allows image fusion between two arbitrary image modalities. A prototype was built for prostate biopsies merging pre-operative magnetic resonance images (MRI) with interventional 3D free-hand transrectal US (TRUS). Methods The fusion between MRI and TRUS images was performed by replacing the inter-modal MRI-TRUS registration by an intra-modal 3D/3D-US/TRUS registration and a pre-operative image fusion between MRI and 3D(-abdominal)-US using an optical tracking system (OTS). The error of the inter-modal MRI/3D(-abdominal)-US image fusion was evaluated using a multi-cone phantom and a prostate phantom by calculating a target registration error (TRE) and the Dice score of segmented lesions (radius 5 mm) from the prostate phantom. The pre-operative 3D(-abdominal)-US was then registered with the TRUS images and the TRE error was calculated. Finally, a Dice score of segmented lesions between TRUS and MRI was determined. Results The fiducial registration error for the 3D(-abdominal)-US and TRUS calibration resulted in 0.87 mm and 1.18 mm, respectively. The TRE for the 3D abdominal transducer was 1.08 mm. The TRE of the MRI/3D-US image fusion using a multi-cone phantom was 1.81 mm. The Dice-score calculated from test lesions segmented in MRI and TRUS resulted in an error of 0.67. The TRE between the 3D-US and the TRUS was 2.10 mm. The Dice score from segmented lesions in MRI and TRUS was 0.67. Conclusions The intra-modal registration via OTS between MRI and TRUS images showed sufficient accuracy for prostate biopsy.

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 (FWHM avg ) 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 FWHM avg 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.