Difference In Signal-to-noise Ratio Research Articles

Feasibility of improving image performance in photon-counting computed tomography using X-ray spectrum filtration

Photon-counting computed tomography (PCCT) is an emerging technology based on new energy-resolving X-ray detectors (photon-counting detectors (PCDs)) that provide promising image performance compared to the conventional energy-integrating CT (EICT). It has the potential to provide higher resolution and contrast, lower radiation dose, and fewer artifacts, which has led to significant research interest. This study proposes a method to further improve the image performance of the PCCT using an X-ray spectrum filtration technique. We conducted a feasibility study via simulations using aluminum (Al), beryllium (Be), sodium (Na), nickel (Ni), tin (Sn), neodymium (Nd), and tantalum (Ta) incorporating varying thicknesses using a PCD simulation toolkit (PcTK). The PCCT system used in this simulation was modeled to have a cadmium telluride-based PCD with four multi-energy thresholds of E = 40, 60, 80, 100 keV, assuming that the object received the same number of photons. Using the PCCT images obtained with the highest threshold (i.e., E4 = 100 keV), the image quality was evaluated quantitatively in terms of the signal difference-to-noise ratio (SDNR) and structural similarity (SSIM). Among the filtrations selected in this simulation, a filtration of 2.0 mmAl (inherent) and 1.5 mmSn (added) showed the best image quality. The SDNR and SSIM values measured in the PCCT image obtained with an added filtration of 1.5 mmSn were 3.73 and 0.81, approximately 1.9 and 1.8 times higher than those with no added filtration, respectively. Consequently, the X-ray spectrum filtration technique in PCCT is useful to further improve image performance.

Automatic image quality evaluation in digital radiography using for-processing and for-presentation images.

To investigate the impact of digital image post-processing algorithms on various image quality (IQ) metrics of radiographic images under different exposure conditions. A custom-made phantom constructed according to the instructions given in the IAEA Human Health Series No.39 publication was used, along with the respective software that automatically calculates various IQ metrics. Images with various exposure parameters were acquired with a digital radiography unit, which for each acquisition produces two images: one for-processing (raw) and one for-presentation (clinical). Various examination protocols were used, which incorporate diverse post-processing algorithms. The IQ metrics' values (IQ-scores) obtained were analyzed to investigate the effects of increasing incident air kerma (IAK) on the image receptor, tube potential (kVp), additional filtration, and examination protocol on image quality, and the differences between image type (raw or clinical). The IQ-scores were consistent for repeated identical exposures for both raw and clinical images. The effect that changes in exposure parameters and examination protocol had on IQ-scores were different depending on the IQ metric and image type. The expected positive effect that increasing IAK and decreasing tube potential should have on IQ was clearly exhibited in two IQ metrics only, the signal difference-to-noise-ratio (SDNR) and the detectability index (d'), for both image types. No effect of additional filtration on any of the IQ metrics was detected on images of either type. An interesting finding of the study was that for all different image acquisition selections the d' scores were larger in raw images, whereas the other IQ metrics were larger in clinical images for most of the cases. Since IQ-scores of raw and their respective clinical images may be largely different, the same type of image should be consistently used for monitoring IQ constancy and when results from different X-ray systems are compared.

Effect of Gonadal Protection on Image Quality in Frontal Hip Radiography

In recent years, there has been a growing movement in Western countries toward the abolition of gonadal protection during radiography. The reasons for this recommendation are that there are few reports of increased risk of genetic effects, that the ovarian dose is not due to direct X-rays but due to internally scattered X-rays that cannot be shielded, and that the presence of gonadal protection may adversely affect the automatic exposure control mechanism and may mask important findings. In addition, the gonadal protection is a large high absorber of X-rays, and its presence in the irradiation field may have some effect on image quality, but the effect of the gonadal protection on image quality has not been clarified. In addition, after the abolition of gonadal protection, the optimal irradiation field setting is expected to become even more important to avoid unnecessary exposure. In this study, we investigated the effect of gonadal protection on image quality in frontal hip radiographs of adults with different radiation qualities and clarified the image quality under conditions in which the irradiation field is appropriately narrowed. Frontal hip radiographs were taken using a human phantom as the subject, and the image quality of the femoral head was evaluated. Two irradiation fields were used: (a) 14×17 inch field and (b) an appropriate field (11.6×15 inch) that does not impair the reference line and image information necessary for reading hip joint images. The imaging tube voltage was set at 70 kV, and conditions for adding a copper filter were also considered. The incident surface air kerma was set to 1.25 mGy. The incident surface dose at this time was sufficiently lower than the diagnostic reference level (2.5 mGy) in Japan and was judged to be appropriate for imaging using an indirect conversion flat panel detector. The image quality evaluation item was the signal difference to noise ratio (SdNR) including scatterers. The SdNR decreased by 4.6% when a gonadal shield was placed, indicating that the gonadal shield reduced image quality. When the irradiation field size was appropriately narrowed down, SdNR slightly increased or decreased depending on the quality of the imaging material, but the change was small compared to the change in SdNR with and without the gonadal protection shield. The results of this study confirm that the elimination of gonadal protection in hip radiography has significant advantages, such as reducing unnecessary X-ray exposure while ensuring image quality, when the irradiation field is set appropriately.

Signal-difference-to-noise comparison of temporal subtraction, kV-switching dual-energy and photon-counting dual-energy x-ray angiography.

Dual-energy (DE) x-ray angiography with photon-counting detectors (PCDs) may enable single-exposure DE imaging of coronaryvasculature. To compare the iodine signal-difference-to-noise ratio (SDNR) of single-exposure DE angiography with digital subtraction angiography (DSA) and kV-switching DE angiography for matched patient x-rayexposure. In a phantom study, we determined the technique parameters that maximized the iodine SDNR per root entrance air kerma for DSA, kV-switching DE angiography and single-exposure DE angiography. We measured SDNR from images of a phantom consisting of an iodine step-wedge immersed in a water tank of either 20 or 30cm in thickness. We also imaged a phantom with simulated vessels embedded in background clutter and measured vessel SDNR. For this second phantom, we also applied anti-correlated noise reduction (ACNR) and calculated the resulting iodine SDNR. All images were acquired using a cadmium telluride PCD with two energy bins and analog charge summing for charge sharing suppression. The energy-discrimination capabilities were only used for the single-exposure DE approach. Optimized techniques were compared in terms of SDNR per root air kerma for two levels of x-rayscatter. For the same patient x-ray exposure, the SDNR of single-exposure DE imaging without ACNR was 75% to 85% of that of kV-switching DE imaging (also without ACNR) and DSA, the latter two of which had nearly equal SDNR. The single-exposure DE approach required ∼50% of the tube load of the kV-switching approach to achieve the same SDNR. For matched patient air kermas, the single exposure approach required only ∼25% of the tube load of the kV-switching approach. ACNR increased SDNR by 2.4 and 3.0 for kV-switching and single-exposure DE imaging,respectively. Photon-counting, single-exposure DE angiography can suppress soft tissues and provide iodine SDNR levels comparable to DSA and kV-switching DE angiography for matched patient radiation exposures. When ACNR is used to reduce DE image noise, the SDNR of single-exposure DE imaging and kV-switching DE imaging exceed that of DSA by more than a factor of two. Compared to kV-switching DE imaging, single-exposure DE imaging requires substantially lower tube loading to achieve the sameSDNR.

ANALISIS AUDIT DOSIS SEBAGAI UPAYA OPTIMISASI PADA PEMERIKSAAN CT ABDOMEN INTRAVENOUS (IV) DI RUMAH SAKIT UMUM PUSAT ADAM MALIK MEDAN

Audits are conducted on CT scan examinations using dose metrics to assess the need for optimization in computed tomography procedures. Diagnostic reference levels (DRL) provide an indicator that helps optimize patient medical exposure by adhering to the recommendations of the International Commission on Radiological Protection (ICRP). In the radiology unit at Adam Malik Hospital, efforts were made to reduce the radiation dose given to patients during CT abdominal IV examinations by using the lowest possible radiation dose without compromising image quality. The CT scans were carried out on 1526 patients using a Philips Ingenuity brand CT Scan, type MRC880, serial number 168014, and a built-in phantom as a patient representation. The radiation output was represented by the volumetric computed tomography dose index (CTDIvol) and dose length product (DLP). The physical parameters of tube voltage (kV) and pitch were evaluated to optimize the CT abdominal IV dose. At the same time, the Signal Difference to Noise Ratio (SDNR) was used to analyze image quality for each change in physical parameters. The results of dose audit data for CT abdominal IV patients, when using parameters of 120 kV and 1.1-1.2 pitch, obtained a Q2 value of 1452 mGy.cm higher than I-DRL of 1360 mGy.cm. Data from measurements with a phantom at 100 kV and 1.40-1.48 pitch showed a lower dose than the previous parameters. CT abdominal IV patient dose data with 100 kV and 1.40 -1.48 pitch showed that the DLP value in Q2 was 755 mGy.cm, lower than the previous measurement of 1452 mGy.cm. This means that there was a 52% decrease in dose after changing the parameters of 100 kV and 1.40 -1.48 pitch with image quality remaining optimal. The highest SDNR value of 12 was obtained at 100 kV and 1.48 pitch. The results indicate that it is necessary to establish a new protocol for CT abdominal IV with parameters of 100 kV and 1.40 -1.48 pitch for adult patients over 15 years of age. Keywords: optimization, radiation dose, image quality, CT abdomen

OPTIMISASI DOSIS DAN KUALITAS CITRA PADA PEMERIKSAAN PULMONARY ARTERY CATHETER (PAC) DAN PERCUTANEUS CORONARY INTERVENTION (PCI) SEBAGAI UPAYA PROTEKSI RADIASI PASIEN DI CATHLAB RSUP ADAM MALIK MEDAN

The radiation exposure a patient receives during diagnosis and treatment cannot be fully avoided. However, it is crucial to optimize the radiation dose to ensure it is only as much as needed. The purpose of this study is to minimize the patient's radiation exposure during interventions and produce optimal image quality. To accomplish this, dose optimization and image quality were evaluated during PAC and PCI procedures in the Cathlab room at Adam Malik Hospital using Philips Allura Xper FD20. The study was retrospective, using patient dose audits from January 2020 to February 2023, with 250 PACs and 139 PCI mature patients. The median dose value (Q2) was compared to the National diagnostic reference level (NDRL) third quartile (Q3) value to determine optimal patient dose levels. We used a 28 cm PMMA phantom and a 2 cm imaging quality in-house phantom to represent the patient and a solid-state detector to measure surface dose. Medical physicists, radiographers, cardiologists, and nurses worked together in optimization cycles to ensure dose levels were kept to a minimum. Image quality was assessed by calculating the signal difference-to-noise ratio (SDNR), and images were recorded in DICOM format and analyzed using Image J software. Entrance Surface Air Kerma (ESAK) values were recorded to calculate Figure of Merit (FOM) values for each change in physical parameters. The study showed that the distance between the image detector and the object significantly affects the patient's dose. A distance of 14 cm resulted in a higher dose than a distance of 2 cm. The SDNR value varied with the object image distance (OID) factor, and increasing the object's distance to the image detector did not increase the SDNR value. Setting the OID spacing to a minimum is recommended for PAC and PCI procedures to minimize the patient's radiation exposure. The FOM values were affected by both the ESAK and SDNR values. Keywords: Dose Optimization, Image Quality, objek to image distance (OID), Pulmonary Artery Catheter, Percutaneous Coronary Intervention, Cathlab.

The effect of added filtration on radiation dose and image quality in digital radiography of newborns.

Repeated chest and/or abdomen radiographs are needed on mobile digital radiography (DR) units to assess infants' health status. Optimization of DR tube peak kilovoltage (kVp) and tube current time product (mAs) to derive images of diagnostic quality at as low as reasonably achievable radiation dose has been a challenging task. To investigate the effect of exposure parameters and additional filtration on entrance skin dose and image quality in newborn DR imaging. A physical anthropomorphic phantom that simulates the average full-term neonate was used. Chest and chest/abdomen DR images were acquired at the manufacturer's recommended kVp/mAs exposure parameters followed by a series of image acquisitions at different kVp/mAs and beam filtration combinations. Entrance skin dose (ESD) and signal difference to noise ratio (SdNR) for soft tissue, bone and feeding gastric tube were estimated in raw unprocessed images. A figure of merit (FOM) analysis provided the kVp/mAs and filtration that generated images of adequate quality at the lowest ESD. Signal difference increased with kVp and progressively decreased with increasing filtration. Compared to the manufacturer's recommended 53 kVp/1.6 mAs exposure parameters, ESD was reduced by 76% (47.61μGy versus 11.3μGy) in the chest and 66% (47.61μGy versus 16.14μGy) in the chest/abdomen when the exposure parameters and additional beam filtration provided by the FOM analysis were used. The results derived from this phantom study suggest that additional beam filtration along with the appropriate leverage of exposure parameters can lower ESD while maintaining image quality in full-term newborns.

Optimization of chest CT protocols based on pixel image matrix, kernels and iterative reconstruction levels – A phantom study

IntroductionThis study investigated the impact of high matrix image reconstruction in combination with different reconstruction kernels and levels of iterative reconstructions on image quality in chest CT. MethodsAn anthropomorphic chest phantom (Kyoto Kagaku Co., Ltd., Kyoto, Japan), and a Catphan® 600 (The Phantom Laboratory, Greenwich, NY, USA) phantom were scanned using a dual source scanner. Standard institutional protocol with 512 × 512 matrix was used as a reference. Reconstructions were performed for 768 × 768 and 1024 × 1024 matrices and all possible combinations of three different kernels and five levels of iterative reconstructions were included. Signal difference to noise ratio (SdNR) and line pairs per cm (lp/cm) were manually measured. A Linear regression model was applied for objective image analysis (SdNR) and inter–and intra-reader agreement was given as Cohen's kappa for the visual image assessment. ResultsMatrix size did not have a significant impact on SdNR (p = 0.595). Kernel (p = 0.014) and ADMIRE level (p = 0.001) had a statistically significant impact on SdNR. The spatial resolution ranged from 7 lp/cm to 9 lp/cm. The highest spatial resolution was achieved using kernel Br64 and ADMIRE 1, 2 and 3 in both 768- and 1024-matrices, and with Br59 with ADMIRE 2 and 4 and 768-matrix, all visualizing 9 lp/cm. Both readers scored kernel Br59 highest, and the scoring increased with increasing levels of Iterative Reconstruction. ConclusionMatrix size did not influence image quality, however, the choice of kernel and degree of IR had an impact on objective and visual image quality in 768 - and 1024-matrices, suggesting that increased degree of IR may improve diagnostic image quality in chest CT. Implications for practiceImage quality in CT of the lung may be improved by increasing the level of IR.

Resolution aware nonconvex quasinorm iterative digital breast tomosynthesis imaging

Digital breast tomosynthesis is a promising modality providing 3D cross sectional images of breast. However, reconstructing the image from few projections is still a challenging task. We introduce an anisotropic total variation regularized reconstruction method which exploits varying resolution along transverse and sagittal planes by adapting the weights of TV gradients. Moreover, we also investigate if non-convex ℓp quasinorm with p ∈ (0,1) can help to improve the performance of anisotropic TV in detecting micro calcifications and spheroidal masses. The contrast to noise ratio (CNR) for in-plane quality, full with at half maximum (FWHM) of artefact spread function (ASF) for resolution in the z-axis, signal difference to noise ratio (SdNR), and quality factor (QF) for a comprehensive evaluation were used in quantitative analyses and comparisons. For low contrast analysis, QF value of the proposed method for p = 0.9 is 0.18 whereas QF value of isotropic TV with ℓ1 and ℓ2 norms are 0.15 and 0.14, respectively. For high contrast features such as micro-calcifications, although the best CNR value changes with different p values, the majority of the best CNR values are calculated for values 0.8 and 0.9. Overall, the results show that the proposed method, anisotropic TV with non-convex ℓp quasinorm, outperforms isotropic TV with ℓ1 and ℓ2 norms by recovering small micro calcifications and spheroidal masses with higher CNR and increased depth resolution. The proposed method shows the best performance for p values of 0.8 ≤ p < 1.

Dose-reduction Efficiency by Breast Compression in Digital Mammography

Although breast compression has been an efficient practice to reduce the breast dose in mammography, there may be some differences between analog and digital systems. The purpose of this study was to evaluate the dose-reduction efficiency by breast compression in digital mammography under its own criterion that signal difference-to-noise ratio (SDNR) be kept at a certain value. By adopting SDNR as an image quality indicator and average glandular dose (AGD) as a dose indicator, we measured SDNR versus AGD relationship for each breast depth. Then by utilizing figure of merit (FOM), we calculated the breast depth that we had to reduce for halving the breast dose while keeping the SDNR. To halve the dose, 1.49 cm compression was necessary for 0% breast density, 1.25 cm for 50%, and 1.06 cm for 100%. Through FOM analysis, we quantitatively revealed the dose-reduction efficiency by breast compression in digital mammography.

AQAFI: a bioanalytical method for automated KPIs quantification of fluorescent images of human leukocytes and micro-nano particles.

Micro-nanoparticle and leukocyte imaging find significant applications in the areas of infectious disease diagnostics, cellular therapeutics, and biomanufacturing. Portable fluorescence microscopes have been developed for these measurements, however, quantitative assessment of the quality of images (micro-nanoparticles, and leukocytes) captured using these devices remains a challenge. Here, we present a novel method for automated quality assessment of fluorescent images (AQAFI) captured using smartphone fluorescence microscopes (SFM). AQAFI utilizes novel feature extraction methods to identify and measure multiple features of interest in leukocyte and micro-nanoparticle images. For validation of AQAFI, fluorescent particles of different diameters (8.3, 2, 1, 0.8 μm) were imaged using custom-designed SFM at a range of excitation voltages (3.8-4.5 V). Particle intensity, particle vicinity intensity, and image background noise were chosen as analytical parameters of interest and measured by the AQAFI algorithm. A control method was developed by manual calculation of these parameters using ImageJ which was subsequently used to validate the performance of the AQAFI method. For micro-nanoparticle images, correlation coefficients with R2 > 0.95 were obtained for each parameter of interest while comparing AQAFI vs. control (ImageJ). Subsequently, key performance indicators (KPIs) i.e., signal difference to noise ratio (SDNR) and contrast to noise ratio (CNR) were defined and calculated for these micro-nano particle images using both AQAFI and control methods. Finally, we tested the performance of the AQAFI method on the fluorescent images of human peripheral blood leukocytes captured using our custom SFM. Correlation coefficients of R2 = 0.99 were obtained for each parameter of interest (leukocyte intensity, vicinity intensity, background noise) calculated using AQAFI and control (ImageJ). A high correlation was also found between the CNR and SDNR values calculated using both methods. The developed AQAFI method thus presents an automated and precise way to quantify and assess the quality of fluorescent images (micro-nano particles and leukocytes) captured using portable SFMs. Similarly, this study finds broader applicability and can also be employed with benchtop microscopes for the quantitative assessment of their imaging performance.

Optimizing effective dose and image quality in cone beam CT sialography

The purpose of this study was to develop protocols that optimize patient radiation dose and image quality for cone beam computed tomographic (CBCT) sialography for the major salivary glands. Radiation absorbed dose measurements were repeated in triplicate using 25 sites in the head and neck of a Radiation ANalog DOsimetry system (RANDO) phantom, and effective doses were calculated across a range of peak kilovoltage (kVp) and milliamperage (mA) settings using an 8 cm (diameter) by 5 cm (height) field of view (FOV) for submandibular imaging and an 8 cm (diameter) by 8 cm (height) FOV for parotid imaging. Image signal difference-to-noise ratio (SDNR) was determined, and the figure-of-merit (FOM), a measure of image quality, was calculated. For submandibular sialography, 85 kVp and 6 mA were chosen as the optimal exposure parameters, resulting in a mean effective dose of 82.47 µSv and a mean SDNR of 13.86, with a mean FOM of 2.33 µSv-1. For parotid sialography, 70 kVp and 6 mA were chosen, and these settings resulted in a mean effective dose of 39.99 µSv, a mean SDNR of 17.43, and a mean FOM of 7.60 µSv-1. Low-dose 3-dimensional sialography with high image quality and minimal effective dose can be delivered using CBCT with localized, small FOVs.

Experimental optimization of single-exposure dual-energy angiography with photon-counting x-ray detectors.

Photon-counting x-ray detectors may enable single-exposure dual-energy (DE) x-rayangiography. The purpose of this paper is to experimentally optimize the energy thresholds and tube voltage for single-exposure DE x-rayangiography. We optimized single-exposure DE x-ray angiography using the iodine signal-difference-to-noise ratio (SDNR) per root patient air kerma (κ) as a figureof merit. We measured the iodine SDNR by imaging an iodine stepwedge immersed in a water tank with a depth of 30cm in the direction of x-ray propagation. The stepwedge was imaged using tube voltages ranging from 90 to 150kV and a cadmium telluride (CdTe) x-ray detector with two energy bins and analog charge summing for charge sharing suppression. The energy threshold that separates the two energy bins was varied from approximately 35keV to approximately 75% of the maximum energy of the x-ray beam. Curve fitting was used to determine the threshold that maximized . The effect of scatter was determined from measurements of the scatter-to-primary ratios (SPRs) of the low-energy and high-energy images and a semi-empirical model of the relationship between SDNR and SPR. Using the optimal parameters, we imaged a phantom with vessel-simulating structures and backgroundclutter. The optimal energy thresholds increased monotonically from ∼50 to ∼85keV over the range of tube voltages considered. For tube voltages greater than 90kV, the optimal energy thresholds consistently allocated approximately two thirds of all detected primary photons to the low energy bin; this ratio was preserved without scatter. Consistent with prior modeling studies, increased monotonically with tube voltage from 90 to 150kV; at 150kV was approximately 38% higher than that at 90kV for an iodine area density of ∼50mg/cm2 . Scatter reduced SDNR by approximately 25% for SPRs of ∼1 and 0.4 in low-energy and high-energy images, respectively. Achieving optimal image quality in single-exposure DE angiography with photon-counting x-ray detectors will require high tube voltages (i.e.,>130kV) and, for thick patients, energy thresholds that allocate approximately two thirds of all primary photons to the low-energy image. Future work will compare the image quality of singe-exposure photon-counting and kV-switching approaches to DE x-rayangiography.

Effect of cone-beam CT detector size and projection geometry on scatter-induced image noise

<h3>Objective</h3> The aim of this study was to evaluate the effect of detector size with different projection geometries on scatter-induced image noise in cone beam computed tomography (CBCT). <h3>Study Design</h3> A polymethyl methacrylate phantom containing air and aluminum underwent CBCT scanning positioned in the center of the FOV. Images were acquired with the PaX-i3D Green Premium (Vatech, Korea), which has a narrow vertical detector with off-axis projection geometry and multiple consecutive rotations for small and medium FOVs; the OP300 3D Maxio (Instrumentarium Dental, Tuusula, Finland), with aligned projection geometry for small FOV, and off-axis geometry for medium FOV; and the Promax 3D Max (Planmeca, Helsinki, Finland), which has aligned geometry for small and medium FOVs. Scans were performed using small and medium FOVs, combining tube voltages and tube currents to maintain a fixed normalized dose-area product. Signal difference-to-noise ratio (SDNR) was calculated on two-dimensional projection images and compared using one-way ANOVA with post hoc Tukey tests (α =0.05) between CBCT units. <h3>Results</h3> For small FOVs, Promax showed the highest SDNR compared to OP300 and PaX-i3D, with the difference being statistically significant (p < 0.0001). OP300 exhibited significantly higher SDNR values than PaX-i3D (p < 0.0001). For medium FOVs, Promax had significantly higher SDNR than OP300 and PaX-i3D (p < 0.0001), and no difference was discovered between OP300 and PaX-i3D. Therefore, Promax had the lowest scatter-induced image noise since it has aligned projection geometry in small and medium FOV sizes. For OP300, which has an off-axis geometry, the scatter-induced image noise with the medium FOV was comparable to PaX-i3D. <h3>Conclusion</h3> Reducing the active area of the detector does not result in fewer scattered photons reaching the detector, as it needs more rotations to capture all the projections. Moreover, in off-axis projections there is a lateral off-set of the detector, which results in the center of the FOV being positioned in the edges of the projection images. <b>Statement of Ethical Review</b> Ethical review was sought and study was exempted from ethical review

In vitro measurements of radiation exposure with different modalities (computed tomography, cone beam computed tomography) for imaging the petrous bone with a pediatric anthropomorphic phantom

BackgroundVarious imaging modalities, such as multi-detector computed tomography (CT) and cone beam CT are commonly used in infants for the diagnosis of hearing loss and surgical planning of implantation hearing aid devices, with differing results.ObjectiveWe compared three different imaging modalities available in our institution, including a high-class CT scanner, a mid-class CT scanner and an angiography system with a cone beam CT option, for image quality and radiation exposure in a phantom study.Materials and methodsWhile scanning an anthropomorphic phantom imitating a 1-year-old child with vendor-provided routine protocols, organ doses, surface doses and effective doses were determined for these three modalities with thermoluminescent dosimeters. The image quality was evaluated using the signal difference to noise ratio (SDNR) and the spatial resolution of a line-pair insert in the phantom head. The dose efficiency, defined as the ratio of SDNR and effective dose, was also compared.ResultsThe organ and surface doses were lowest with the high-class CT protocol, but the image quality was the worst. Image quality was best with the cone beam CT protocol, which, however, had the highest radiation exposure in this study, whereas the mid-class CT was in between.ConclusionBased on our results, high-end CT should be used for surgical planning because it has the lowest dose, while the image quality is still sufficient for this purpose. However, if highest image quality is needed and required, e.g., by ENT surgeons, the other modalities should be considered.

Cone-beam breast CT using an offset detector: effect of detector offset and image reconstruction algorithm

Objective. A dedicated cone-beam breast computed tomography (BCT) using a high-resolution, low-noise detector operating in offset-detector geometry has been developed. This study investigates the effects of varying detector offsets and image reconstruction algorithms to determine the appropriate combination of detector offset and reconstruction algorithm. Approach. Projection datasets (300 projections in 360°) of 30 breasts containing calcified lesions that were acquired using a prototype cone-beam BCT system comprising a 40 × 30 cm flat-panel detector with 1024 × 768 detector pixels were reconstructed using Feldkamp–Davis–Kress (FDK) algorithm and served as the reference. The projection datasets were retrospectively truncated to emulate cone-beam datasets with sinograms of 768 768 and 640 768 detector pixels, corresponding to 5 cm and 7.5 cm lateral offsets, respectively. These datasets were reconstructed using the FDK algorithm with appropriate weights and an ASD-POCS-based Fast, total variation-Regularized, Iterative, Statistical reconstruction Technique (FRIST), resulting in a total of 4 offset-detector reconstructions (2 detector offsets × 2 reconstruction methods). Signal difference-to-noise ratio (SDNR), variance, and full-width at half-maximum (FWHM) of calcifications in two orthogonal directions were determined from all reconstructions. All quantitative measurements were performed on images in units of linear attenuation coefficient (1/cm). Results. The FWHM of calcifications did not differ (P > 0.262) among reconstruction algorithms and detector formats, implying comparable spatial resolution. For a chosen detector offset, the FRIST algorithm outperformed FDK in terms of variance and SDNR (P < 0.0001). For a given reconstruction method, the 5 cm offset provided better results. Significance. This study indicates the feasibility of using the compressed sensing-based, FRIST algorithm to reconstruct sinograms from offset-detectors. Among the reconstruction methods and detector offsets studied, FRIST reconstructions corresponding to a 30 cm × 30 cm with 5 cm lateral offset, achieved the best performance. A clinical prototype using such an offset geometry has been developed and installed for clinical trials.

Quantitative Analysis for the Delineation of the Subthalamic Nuclei on Three-Dimensional Stereotactic MRI Before Deep Brain Stimulation Surgery for Medication-Refractory Parkinson's Disease.

Delineation of the subthalamic nuclei (STN) on MRI is critical for deep brain stimulation (DBS) surgery in patients with Parkinson’s disease (PD). We propose this retrospective cohort study for quantitative analysis of MR signal-to-noise ratio (SNR), contrast, and signal difference-to-noise ratio (SDNR) of the STN on pre-operative three-dimensional (3D) stereotactic MRI in patients with medication-refractory PD. Forty-five consecutive patients with medication-refractory PD who underwent STN-DBS surgery in our hospital from January 2018 to June 2021 were included in this study. All patients had whole-brain 3D MRI, including T2-weighted imaging (T2WI), T2-weighted fluid-attenuated inversion recovery (FLAIR), and susceptibility-weighted imaging (SWI), at 3.0 T scanner for stereotactic navigation. The signal intensities of the STN, corona radiata, and background noise were obtained after placing regions of interest (ROIs) on corresponding structures. Quantitative comparisons of SNR, contrast, and SDNR of the STN between MR pulse sequences, including the T2WI, FLAIR, and SWI. Subgroup analysis regarding patients’ sex, age, and duration of treatment. We used one-way repeated measures analysis of variance for quantitative comparisons of SNR, contrast, and SDNR of the STN between different MR pulse sequences, and we also used the dependent t-test for the post hoc tests. In addition, we used Mann–Whitney U test for subgroup analyses. Both the contrast (0.33 ± 0.07) and SDNR (98.65 ± 51.37) were highest on FLAIR (all p < 0.001). The SNR was highest on SWI (276.16 ± 115.5), and both the SNR (94.23 ± 31.63) and SDNR (32.14 ± 17.23) were lowest on T2WI. Subgroup analyses demonstrated significantly lower SDNR on SWI for patients receiving medication treatment for ≥13 years (p = 0.003). In conclusion, on 3D stereotactic MRI of medication-refractory PD patients, the contrast and SDNR for the STN are highest on FLAIR, suggesting the optimal delineation of STN on FLAIR.

Technical note: Design and initial evaluation of a novel physical breast phantom to monitor image quality in digital breast tomosynthesis.

To describe the creation process of a new breast phantom specifically designed to monitor quality control (QC) metrics consistency over several months in digital breast tomosynthesis (DBT). The semi-anthropomorphic Tomomam® phantom was designed and evaluated twice monthly on a single Hologic Selenia Dimensions® unit over 5 months. The phantom is manufactured in a one-piece epoxy resin homogeneous material as the basis for manufacturing, simulating breast tissue as 50% equivalent glandular (GL)/50% equivalent adipose (AD) and compressed thickness of 60mm. The distribution of test objects on different planes inside the phantom should allow the quantification of 10 image quality metrics: reproducibility, signal difference-to-noise ratio (SDNR), geometric distortions in the plane, missing or added tissue at chest wall, at the top and bottom of images stack and lateral sides, in-plane homogeneity, image scoring, artifact spread function (ASF), geometric distortions in the volume. SDNR was quantified according to GL and AD tissues. Tolerance criteria per parameter were described to analyze results over the study time. Mean scores were equal to 15.4, 15.0, and 11.6 for masses, microcalcifications, and fibers, respectively. A large difference between GL and AD tissues for SDNR metrics was noted over the study time: the best results were obtained from GL tissues. Both geometric distortions and local homogeneity in the plane conformed to expected values. The mean volume value of the triangular prism was 11.3% greater than the expected value due to a reconstruction height equal to 66mm instead of 60mm. In this study, we monitored several QC metrics discriminating GL and AD tissues by using a new breast phantom developed by us. The preliminary clinical tests demonstrated that the Tomomam® phantom could be used to reliably and efficiently track 10 QC metrics with a single acquisition. More data need to be acquired to refine tolerance criteria for some metrics.

Novel phantom for performance evaluation of contrast-enhanced 3D rotational angiography.

This technical note presents an in-house phantom with a specially designed contrast-object module constructed to address the need for three-dimensional rotational angiography (3DRA) testing. The initial part of the study was a brief evaluation on the commercially available phantom used for 3DRA and computed tomography angiography (CTA) to confirm the need for a special phantom for 3D angiography. Once confirmed, an in-house phantom was constructed. The novel phantom was tested to evaluate the basic image performance metrics, i.e., unsharpness (MTF) and noise characterization (NPS), as well as to show its capability for vessel contrast visibility study. The low contrast objects in the commercially available tools dedicated for CT is found to yield significantly lower signal difference to noise ratio (SDNR) when used for 3DRA, therefore deemed inadequate for 3DRA contrast evaluation. The constructed in-house phantom demonstrates a capability to serve for basic imaging performance check (MTF, NPS, and low contrast evaluation) for 3DRA and CTA. With higher and potentially adjustable visibility of contrast objects as artificial vessels, the in-house phantom also makes more clinically relevant tests, e.g., human- or model observer study and task-based optimization, possible. The novel phantom with special contrast object module shows higher visibility in 3DRA compared to the currently available commercial phantom and, therefore, is recommended for use in 3D angiography.

DIR-DBTnet: Deep iterative reconstruction network for three-dimensional digital breast tomosynthesis imaging.

The goal of this study is to develop a three-dimensional (3D) iterative reconstruction framework based on the deep learning (DL) technique to improve the digital breast tomosynthesis (DBT) imaging performance. In this work, the DIR-DBTnet is developed for DBT image reconstruction by mapping the conventional iterative reconstruction (IR) algorithm to the deep neural network. By design, the DIR-DBTnet learns and optimizes the regularizer and the iteration parameters automatically during the network training with a large amount of simulated DBT data. Numerical, experimental, and clinical data are used to evaluate its performance. Quantitative metrics such as the artifact spread function (ASF), breast density, and the signal difference to noise ratio (SDNR) are measured to assess the image quality. Results show that the proposed DIR-DBTnet is able to reduce the in-plane shadow artifacts and the out-of-plane signal leaking artifacts compared to the filtered backprojection (FBP) and the total variation (TV)-based IR methods. Quantitatively, the full width half maximum (FWHM) of the measured ASF from the clinical data is 27.1% and 23.0% smaller than those obtained with the FBP and TV methods, while the SDNR is increased by 194.5% and 21.8%, respectively. In addition, the breast density obtained from the DIR-DBTnet network is more accurate and consistent with the ground truth. In conclusion, a deep iterative reconstruction network, DIR-DBTnet, has been proposed for 3D DBT image reconstruction. Both qualitative and quantitative analyses of the numerical, experimental, and clinical results demonstrate that the DIR-DBTnet has superior DBT imaging performance than the conventional algorithms.