Gantry-based cone-beam CT of the thoracolumbar spine: A phantom comparison with Photon-Counting CT and Energy-Integrating CT.

Dose optimization for pediatric chest CT: a comparative study of energy-integrating and photon-counting detector CT using 70kV and 100kV protocols with tin filtration regarding image quality and dose exposure.

BACKGROUND: Photon-counting CT (PCCT) may improve dose efficiency compared with energy-integrating detector CT (EID-CT), but evidence remains limited in very young children undergoing non-contrast preoperative chest CT under real-world clinical protocols. OBJECTIVE: To provide a size-aware matched comparison of radiation dose and image quality between PCCT and EID-CT in infants and toddlers (≤ 36 months) undergoing non-contrast preoperative chest CT, and to examine whether the main findings remained directionally consistent across prespecified strata of age, BMI, and water-equivalent diameter (DW). METHODS: In this single-center matched cohort study, a prospective PCCT cohort and a retrospective EID-CT cohort were propensity score–matched 1:1 (49 pairs). Dose metrics (CTDIvol, DLP, SSDE) and objective and subjective image quality were evaluated, with subgroup analyses stratified by age (< 12 vs. ≥ 12 months), BMI tertiles, and DW tertiles. RESULTS: The PCCT group showed significantly lower radiation dose metrics (CTDIvol, DLP, and SSDE) compared to the EID-CT group (P < 0.001). In terms of objective image quality, PCCT significantly reduced image noise in all lung lobes and consistently demonstrated higher signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) (all P < 0.001). Subjective image quality assessments showed no significant difference between PCCT and EID-CT (P > 0.05). Across prespecified age, BMI, and DW strata, PCCT remained associated with lower dose metrics and favorable objective image-quality trends, although these subgroup findings should be interpreted as exploratory. CONCLUSION: In this matched cohort of infants and toddlers undergoing non-contrast preoperative chest CT, PCCT was associated with substantially lower radiation dose and improved objective image quality compared with EID-CT, and no statistically significant difference was detected in subjective image quality scores between PCCT and EID-CT.

C-arm Cone-beam CT: General Principles and Technical Considerations for Use in Interventional Radiology

A comparative evaluation of Cone Beam Computed Tomography (CBCT) and Multi-Slice CT (MSCT): Part I. On subjective image quality

Comparison of Low Dose Performance of Photon-Counting and Energy Integrating CT

Background Although energy-integrating detector (EID) CT remains the standard in diagnosing and monitoring lung cancer, it has limitations compared with photon-counting CT (PCCT). However, the role of low-dose PCCT in evaluating lung cancer remains unexplored. Purpose To compare the diagnostic quality of chest CT images from PCCT with a low radiation dose and a low injection rate, volume, and concentration of contrast agent (hereafter, a "quadruple-low protocol") with that of EID CT in patients with lung cancer. Materials and Methods This retrospective study included patients with lung cancer undergoing PCCT or EID CT between July 2024 and September 2024. Patients underwent PCCT with the low radiation dose plus reduced contrast agent protocol (quadruple-low protocol: 2.0 mL/sec injection rate, 1.0 mL/kg of 320 mg of iodine per milliliter) and EID CT with a conventional protocol. Two radiologists independently evaluated the subjective image quality and lesion imaging features. Lesion and parenchymal metrics (attenuation, signal-to-noise ratio [SNR], and contrast-to-noise ratio [CNR]) were also assessed. Data were compared using the Student t test, Mann-Whitney U test, or multivariable regression. Sensitivity analysis was performed using propensity score matching. Results Among 425 participants (mean age, 61 years ± 9.5 [SD]; 273 men), PCCT reduced radiation dose by 55% (mean effective dose, 3.49 mSv ± 0.91 vs 7.82 mSv ± 2.15; P < .001) while lowering contrast agent injection rate, volume, and concentration by 33% (P < .001), 22% (P < .001), and 9% (P < .001), respectively. PCCT reduced the incidence of contrast-induced nephropathy (CIN) compared with EID CT (0% [0 of 120] vs 7.9% [24 of 305], P = .02). PCCT also exhibited higher objective SNR and CNR in lung lesions and parenchyma, with superior subjective image quality scores and increased diagnostic confidence for imaging features (all adjusted P < .001). Results remained consistent in sensitivity analysis. Conclusion Compared with EID CT, PCCT with a quadruple-low protocol reduced the incidence of CIN and enhanced image quality and diagnostic confidence in imaging features in patients with lung cancer. © RSNA, 2026 Supplemental material is available for this article.

To compare radiation doses in cone beam computed tomography (CBCT) with those of multi-detector computed tomography (MDCT) using manufacturers' standard protocols. Dose-levels in head and abdominal imaging were evaluated using a dosimetric phantom. Effective dose estimates were performed by placing thermoluminescent dosimeters in the phantom. Selected protocols for two CBCT systems and comparable protocols for one MDCT system were evaluated. Organ doses were measured and effective doses derived by applying the International Commission on Radiological Protection 2007 tissue weighting factors. Effective doses estimated for the head protocol were 4.4 and 5.4 mSv for the two CBCT systems respectively and 4.3 mSv for MDCT. Eye doses for one CBCT system and MDCT were comparable (173.6 and 148.4 mGy respectively) but significantly higher compared with the second CBCT (44.6 mGy). Two abdominal protocols were evaluated for each system; the effective doses estimated were 15.0 and 18.6 mSv, 25.4 and 37.0 mSv, and 9.8 and 13.5 mSv, respectively, for each of the CBCT and MDCT systems. The study demonstrated comparable dose-levels for CBCT and MDCT systems in head studies, but higher dose levels for CBCT in abdominal studies. There was a significant difference in eye doses observed between the CBCT systems. • Cone beam computed tomography (CBCT) is increasingly utilised in interventional radiology. • Effective doses for selected CBCT and MDCT protocols were estimated and compared. • Dose levels in CBCT and MDCT were comparable for head studies. • Dose levels were higher in CBCT for abdominal studies.

The aim was to compare the image quality of photon-counting detector CT (PCD-CT) and energy-integrating detector CT (EID-CT) in patients with tibial plateau fractures treated with metallic osteosynthesis material, and to identify optimal reconstruction parameters for PCD-CT. After ethical approval, twelve patients underwent PCD-CT and EID-CT scans. Images were reconstructed using bone and soft-tissue kernels with metal artifact reduction (iMAR). PCD-CT virtual monoenergetic images (VMI) at 70, 110, and 150 keV were generated. Five radiologists assessed metal artifact severity and bone and soft-tissue visualization using a 7-point Likert scale. Visual grading characteristics analysis was performed. Noise levels were quantified and compared using Wilcoxon's signed-rank test. EID-CT was rated superior in reducing metal-artifact streaks (AUC: 0.10-0.21). No significant difference was found between EID-CT iMAR and PCD-CT VMI at 110 keV and 150 keV (AUC: 0.40-0.49) concerning the metal-bone interface. An ultra-high-resolution PCD-CT kernel outperformed its EID-CT counterpart in bone visualization, with AUC values of 0.67-0.92 across all bone criteria, including those incorporating artifact-affected regions. PCD-CT showed lower noise. Metal artifact reduction was superior in EID-CT iMAR images compared to PCD-CT iMAR and VMI 110/150 keV, except at the metal-bone interface, where EID-CT iMAR images and PCD-CT VMI 110/150 keV performed comparably. The ultra-high-resolution PCD-CT kernel provided the best bone visualization, even when artifact-affected areas were included. Noise levels were lower in PCD-CT. This is the first in vivo comparison of photon-counting and energy-integrating CT for postoperative knee imaging with metallic osteosynthesis material. These findings highlight the need for improved metal artifact reduction in PCD‑CT, while demonstrating superior bone visualization, and support a complementary interpretation strategy in postoperative knees using high‑energy VMI and MAR‑corrected reconstructions. Photon-counting CT demonstrated excellent bone visualization. Conventional EID-CT achieved better metal artifact reduction than photon-counting CT. The metal-bone interface was rated similarly for energy-integrating CT and photon-counting CT virtual monoenergetic images. These findings indicate that further improvements in metal artifact reduction algorithms for PCD-CT are warranted.

Photon counting computed tomography (PCCT) employs direct and spectrally resolved counting of individual x-ray quanta, enhancing image quality compared to the standard energy-integrating CT (EICT). To evaluate the quantitative improvements in CT image quality metrics by comparing the first medical PCCT with a state-of-the-art EICT. The PCCT versus EICT noise improvement ratio R was derived from the quantum statistics of the measurement process and measured across the clinical x-ray flux range for both systems. Detector and system modulation transfer functions (MTFs) were obtained using tilted-slit and wire phantom measurements. Image root mean square (RMS) noise, noise power spectrum (NPS), and x-ray patient dose were compared using a CatPhan phantom at two identical clinical target resolutions. The measurement of the PCCT noise improvement ratio R showed an elimination of electronic noise and a 10% noise transfer advantage. The PCCT detector MTF exhibited 3x higher angular resolution limits in comparison to EICT and close to ideal sinc behavior due to the electromagnetic formation of pixels in the PCCT semiconductor detector. This translated to 3.5x enhancements in CT system MTF ratios at 10 LP/cm, reflecting a significant improvement in millimeter range CT imaging. Both the improved quantum detection and the system MTF ratio improvement contribute to the measured 3x enhancements in image NPS at 10 LP/cm for identical image target resolution. An improvement of up to 1.7x in RMS image noise was observed accordingly. For low and ultra-low dose imaging with image filtering, dose efficiency increased between 2x and 10x, demonstrating the PCCT's capability to advance CT ultra-low dose imaging. The direct counting detection in PCCT has been shown to significantly improve sinogram noise and detector MTF ratios compared to energy integrating EICT. The observed translations into CT system MTF, image NPS, image noise, and dose ratios reflect a paradigm shift for CT image quality and dose efficiency.

Evaluation of Radiation Dose and Image Quality for the Varian Cone Beam Computed Tomography System

Cone Beam Computed Tomography (CBCT) has gained a broad acceptance in dentomaxillofacial imaging. Computed Tomography (CT) is another imaging modality for diagnosis and preoperative assessments of the head and neck region. Considering the increased radiation exposure and high cost of CT, this study sought to subjectively assess the image quality of CBCT and Multi Slice CT (MSCT). A dry human mandible was scanned by five CBCT systems (New Tom 3G, Scanora, CRANEX 3D, Promax and Galileos) and one MSCT system. Three independent oral and maxillofacial radiologists reviewed the CBCT and MSCT scans for the quality of 10 landmarks namely mental foramen, trabecular bone, Periodontal Ligament (PDL), dentin, incisive canal, mandibular canal, dental pulp, enamel, lamina dura and cortical bone using a five-point scale. Significant differences were found between MSCT and CBCT and among the five CBCT systems (p<0.05) in visualization of different anatomical structures. A fine structure such as the incisive canal was significantly less visible and more variable among the systems in comparison with other anatomical landmarks such as the mental foramen, mandibular canal, cortical bone, dental pulp, enamel and dentin (p<0.05). The Cranex 3D and Promax systems were superior to MSCT and all other CBCT systems in visualizing anatomical structures. The CBCT image quality was superior to that of MSCT even though some variability existed among different CBCT systems in visualizing fine structures. Considering the low radiation dose and high resolution, CBCT may be beneficial for dentomaxillofacial imaging.

The purpose of this study is to determine if a universal 120-kV ultra-high pitch and virtual monoenergetic images (VMIs) protocol on the photon-counting computed tomography (PCCT) system can provide sufficient image quality for pediatric abdominal imaging, regardless of size, compared with protocols using a size-dependent kV and dual-source flash mode on the energy-integrating CT (EICT) system. One solid water insert and 3 iodine (2, 5, 10 mg I/mL) inserts were attached or inserted into phantoms of variable sizes, simulating the abdomens of a newborn, 5-year-old, 10-year-old, and adult-sized pediatric patients. Each phantom setting was scanned on an EICT using clinical size-specific kV dual-source protocols with a pitch of 3.0. The scans were performed with fixed scanning parameters, and the CTDI vol values of full dose were 0.30, 0.71, 1.05, and 7.40 mGy for newborn to adult size, respectively. In addition, half dose scans were acquired on EICT. Each phantom was then scanned on a PCCT (Siemens Alpha) using a universal 120-kV protocol with the same full dose and half dose as determined above on the EICT scanner. All other parameters matched to EICT settings. Virtual monoenergetic images were generated from PCCT scans between 40 and 80 keV with a 5-keV interval. Image quality metrics were compared between PCCT VMIs and EICT, including image noise (measured as standard deviation of solid water), contrast-to-noise ratio (CNR) (measured at iodine inserts with solid water as background), and noise power spectrum (measured in uniform phantom regions). Noise at a PCCT VMI of 70 keV (7.0 ± 0.6 HU for newborn, 14.7 ± 1.6 HU for adult) is comparable ( P > 0.05, t test) or significantly lower ( P < 0.05, t test) compared with EICT (7.8 ± 0.8 HU for newborn, 15.3 ± 1.5 HU for adult). Iodine CNR from PCCT VMI at 50 keV (50.8 ± 8.4 for newborn, 27.3 ± 2.8 for adult) is comparable ( P > 0.05, t test) or significantly higher ( P < 0.05, t test) to the corresponding EICT measurements (57.5 ± 6.7 for newborn, 13.8 ± 1.7 for adult). The noise power spectrum curve shape of PCCT VMI is similar to EICT, despite PCCT VMI exhibiting higher noise at low keV levels. The universal PCCT 120 kV with ultra-high pitch and postprocessed VMIs demonstrated equivalent or improved performance in noise (70 keV) and iodine CNR (50 keV) for pediatric abdominal CT, compared with size-specific kV images on the EICT.

We aimed to quantitatively compare different computed tomography (CT)-based bone volume fraction (BV/TV) measurements. We hypothesize that phantom-less measurement using virtual monochromatic images (VMI) reconstructed form dual-energy CT (DECT) or photon counting CT (PCT) is less affected by tissue variations in trabecular bone than quantitative CT (QCT) and that PCT allows measurements with a lower radiation dose. The BV/TV of bovine trabecular bone samples were measured using four CT scanning methods. Eight different measurements were compared using three soft tissue substitutes (air, saline solution, and fat) to investigate its effect on BV/TV estimation. For this purpose, the samples' bone marrow was removed and replaced with one of the three substitutes in succession for CT scanning. For QCT, a standard bone phantom was used to derive BV/TV form CT values. While DECT- and PCT-based measurements were based on a system of energy-dependent equations established by reconstructing VMIs for specific photon energies. T-test, ANOVA tests and pairwise comparison were performed using the micro-CT (µCT) measurements as reference standard. QCT showed a significant difference between the fat, saline solution, and air. DECT and especially PCT showed no differences between the substitutes. PCT showed no significant differences between radiation doses. Our results highlight the complexity of BV/TV measurements and emphasize the impact of the trabecular bone components on measurement accuracy. Despite these challenges, VMIs from "low" dose PCT provide a reliable alternative to standard QCT. They have the potential to improve the estimation of bone conditions, as well offering valuable insights for clinical, and forensic applications.

Authors' response.

Quantitative imaging techniques, such as virtual monochromatic imaging (VMI) and iodine quantification (IQ), have proven valuable diagnostic methods in several specific clinical tasks such as tumor and tissue differentiation. Recently, a new generation of computed tomography (CT) scanners equipped with photon-counting detectors (PCD) has reached clinical status. This work aimed to investigate the performance of a new photon-counting CT (PC-CT) in low-dose quantitative imaging tasks, comparing it to an earlier generation CT scanner with an energy-integrating detector dual-energy CT (DE-CT). The accuracy and precision of the quantification across size, dose, material types (including low and high iodine concentrations), displacement from iso-center, and solvent (tissue background) composition wereexplored. Quantitative analysis was performed on two clinical scanners, Siemens SOMATOM Force and NAEOTOM Alpha using a multi-energy phantom with plastic inserts mimicking different iodine concentrations and tissue types. The tube configurations in the dual-energy scanner were 80/150Sn kVp and 100/150Sn kVp, while for PC-CT both tube voltages were set to either 120 or 140 kVp with photon-counting energy thresholds set at 20/65 or 20/70 keV. The statistical significance of patient-related parameters in quantitative measurements was examined using ANOVA and pairwise comparison with the posthoc Tukey honest significance test. Scanner bias was assessed in both quantitative tasks for relevant patient-specificparameters. The accuracy of IQ and VMI in the PC-CT was comparable between standard and low radiation doses (p < 0.01). The patient size and tissue type significantly affect the accuracy of both quantitative imaging tasks in both scanners. The PC-CT scanner outperforms the DE-CT scanner in the IQ task in all cases. Iodine quantification bias in the PC-CT (-0.9 ± 0.15 mg/mL) at low doses in our study was comparable to that of DE-CT (range -2.6 to 1.5 mg/mL, published elsewhere) at a 1.7× higher dose, but the dose reduction severely biased DE-CT (4.72 ± 0.22 mg/mL). The accuracy in Hounsfield units (HU) estimation was comparable for 70 and 100 keV virtual imaging between scanners, but PC-CT was significantly underestimating virtual 40 keV HU values of dense materials in the phantom representing the extremely obesepopulation. The statistical analysis of our measurements reveals better IQ at lower radiation doses using new PC-CT. Although VMI performance was mostly comparable between the scanners, the DE-CT scanner quantitatively outperformed PC-CT when estimating HU values in the specific case of very large phantoms and dense materials, benefiting from increased X-ray tubepotentials.