RPS 404 - Photon counting CT: advances in chest imaging

Author Block: J. Kroschke¹, B. J. Kerber¹, O. Von Stackelberg², F. Ensle¹, L. Jungblut¹, M. O. Wielpütz³, T. Frauenfelder¹, H-U. Kauczor⁴, O. Weinheimer⁴; ¹Zurich/CH, ²Mannheim/DE, ³Greifswald/DE, ⁴Heidelberg/DE
Purpose: Photon-counting computed tomography (PCCT) enables dose reductions to levels comparable to chest radiography, which is of clinical interest for applications such as lung cancer screening. However, quantitative CT (QCT) metrics may be altered at ultra-low dose (ULD). This study evaluated the impact of dose reduction on lung QCT.
Methods or Background: In 101 patients (mean age 61.0±12.5 years), non-contrast low-dose (LD-CT, CTDIvol: ~0.64±0.15 mGy) and radiography-comparable ULD-CT (~0.11±0.03 mGy) scans were acquired in the same session on PCCT, with LD-CT as reference. Using YACTA software fully automated QCT analysis was performed on images reconstructed with a soft kernel (Br36u, strength level 3) for lung parenchyma and a hard kernel (Bl64u, strength level 3) for airways. Two expert readers assessed image quality, emphysema, and airway wall features.
Results or Findings: ULD-CT showed a 66.5% increase in noise for Br36u and 63.9% for Bl64u, reflected in lower visual image quality (p<0.001, κ=0.59). Automated airway segmentation decreased (−41.4, p<0.001), consistent with fewer visible generations (p<0.001, ICC=0.81). Wall percentage remained stable across dose levels, with no significant differences in visually assessed wall thickening (R1 p=0.89, R2 p=0.20).
At ULD, mean lung density (MLD) was reduced 13.5 HU (p<0.001; r²=0.93), leading to a lower 15th percentile (Perc15: −20.2 HU, p<0.001; r²=0.93). Applying a sponge model correction for volume differences decreased bias (MLD: −12.5 HU; Perc15: −19.9 HU) and improved correlations (r²=0.97–0.98). Visually, emphysema extent was consistently underestimated at ULD (p<0.001, κ=0.92).
Conclusion: PCCT at radiography-comparable dose alters QCT metrics, particularly lung density and emphysema quantification. While sponge model correction mitigates these effects, both automated and visual emphysema assessments remain biased, highlighting limitations of the conventional −950 HU cut-off at ULD.
Limitations: Single-center, single-vendor study with limited patient numbers. No HR-CT as reference standard.
Funding for this study: No external funding was provided for this study.
Has your study been approved by an ethics committee? Yes
Ethics committee - additional information: Approval for this study was granted by the local ethics committee (KEK-ZH-NR. 2022-D0008)

Author Block: Z. Zhu¹, K. Xu¹, L. Nicodeme², Q. Wang¹, L. Song¹, Z. Jin¹; ¹Beijing/CN, ²Vienna/AT
Purpose: The accurate quantification of interstitial lung disease (ILD) in idiopathic inflammatory myopathies (IIM) is critical for prognosis but is limited by the radiation dose constraints of conventional CT. This study aimed to evaluate the clinical utility of photon-counting CT (PCCT)-derived quantitative parameters for ILD severity assessment in IIM, comparing standard-dose (SD) and tin-filtered low-dose (LD) protocols.
Methods or Background: In this prospective single-center study, outpatients with IIM-ILD underwent consecutive SD (120 kVp) and LD (Sn100 kVp) PCCT scans between September 2023 and November 2024. Images were reconstructed with 1.0-mm slice thickness. Quantitative ILD features were extracted using an EU-MDR–approved deep learning software. Fibrosis extent was defined as the sum of reticulation, honeycombing, and bronchiectasis. Visual scoring was performed for severity classification. Comparisons were analyzed using Bland–Altman and receiver operating characteristic analyses; correlation tests were assessed with Spearman’s rank correlation coefficients.
Results or Findings: A total of 48 adults with IIM-ILD (40 females; mean age, 53.88 ± 11.13 years) were included. LD scans achieved a substantial dose reduction (CTDVol, 0.77 vs 5.40 mGy) while maintaining high agreement with SD (net differences <1% for all parameters). Low-dose protocols slightly underestimated fibrotic changes, with a mean net difference of -0.64% (95% LOA: −1.83% to 0.54%), whereas they overestimated the extent of ground-glass opacity, with a mean net difference of 0.98% (95% LOA: −1.27% to 3.24%). The reticulation was strongly correlated with FVC% (rho_max = –0.615, P<0.001) and DLCO% (rho_max = –0.726, P<0.001). The total ILD burden strongly distinguished limited from extensive disease (AUCs, 0.876 to 0.881).
Conclusion: LD protocols markedly reduce radiation exposure without compromising accuracy. PCCT provides a reliable and reproducible quantitative assessment of ILD severity in IIM and has the potential to improve longitudinal monitoring in IIM-ILD.
Limitations: None.
Funding for this study: No funding was provided for this study.
Has your study been approved by an ethics committee? Yes
Ethics committee - additional information: This study was approved by the Ethics Committee of Peking Union Medical College Hospital, and all participants provided written informed consent (I-23PJ1459).

Author Block: J. Dittrich¹, C. Van den Berg¹, S. Scharm¹, C. M. Schaefer-Prokop², S. Dettmer¹, F. Wacker¹, G. H. Pöhler¹, H-o. Shin¹; ¹Hannover/DE, ²Amersfoort/NL
Purpose: To establish normative reference ranges for photon-counting CT (PCCT)-derived pulmonary ventilation and perfused blood volume (PBV) in healthy adults, using pulmonary function tests (PFTs) as the clinical reference standard.
Methods or Background: In this prospective, single-centre study (December 2022 - April 2024), 103 healthy adults underwent spirometry-guided inspiratory and expiratory contrast-enhanced PCCT in supine position. Automated lobar segmentation was performed using TotalSegmentator. CT-derived total lung capacity (CT-TLC), residual volume (CT-RV), and vital capacity (CT-VC) were compared with corresponding PFT metrics.
Ventilation (%) was quantified as the relative air-volume change between inspiration and expiration from nonlinearly registered virtual non-contrast images, normalised to inspiratory lung volume. PBV was calculated from inspiratory datasets, normalised to left atrial iodine attenuation, and corrected for lung inflation by fixing mean parenchymal attenuation at -850 Hounsfield Units. Reference ranges were expressed as mean ± standard deviation and 5th-95th percentiles. Associations with sex, age, lung region, and gravitational orientation were statistically analysed.
Results or Findings: The final cohort included 91 participants (mean age, 53±12 years; 49 men). CT-derived lung volumes were lower than corresponding PFT values but strongly correlated (CT-TLC r=0.89; CT-RV r=0.80; CT-VC r=0.82). Mean ventilation was 59.5 ± 8.5% (42.1%-72.5%), normalised mean PBV was 12.4 ± 2.5% (8.8%-16.8%).
PBV was higher in women than men (P=0.03), and both ventilation and PBV declined with age (P<0.001). Regionally, ventilation was higher in lower versus upper lobes (P=0.003), whereas PBV was higher in upper versus lower lobes (P=0.01). Both parameters exhibited a dorsal>ventral gradient (P<0.001).
Conclusion: This study defines normative reference ranges for PCCT-derived lung ventilation and PBV in healthy adults. Both parameters are influenced by demographic and regional factors and demonstrate characteristic gravitational gradients.
Limitations: Single-centre design; no assessment of scan-rescan repeatability.
Funding for this study: Part of the study was funded by DigiStrucMed (Else-Kröner-Foundation).
Has your study been approved by an ethics committee? Yes
Ethics committee - additional information: This study was approved by the German Federal Office for Radiation Protection (BfS) and by the local ethics committee of Medical School Hannover (number 10077_BO_S_2021 StrSchVO).

Author Block: F-j. FERETZ, Y. Gaillandre, A. Hutt, S. Khung, P. Felloni, B. Longere, C. V. Gkizas, J-B. Faivre, F. A. Pontana; Lille/FR
Purpose: To compare the detection and characterization of interstitial lung disease (ILD) elementary lesions in systemic sclerosis using ultra-high-resolution (UHR) photon-counting detector CT (PCCT) versus high-resolution CT (HRCT) from a third-generation dual-source energy-integrating detector CT.
Methods or Background: This retrospective study included 22 patients with systemic sclerosis and ILD (15 women; mean age: 62.8 years), each undergoing both HRCT and PCCT-UHR for follow-up with clinical and functional stability between scans. HRCT parameters: collimation 2×96×0.6 mm; pitch 2; Sn150kV; 150 mAs with automatic modulation; 1 mm slices; 512² matrix; Bl57 kernel; iterative reconstruction (ADMIRE level 4). PCCT-UHR parameters: collimation 2×120×0.2 mm; pitch 2; Sn100kV or Sn140kV depending on body habitus; automatic tube current modulation (IQ level 36); 0.2 mm slices; 1024² matrix; Bl60 kernel; QIR level 4. Image analysis included tracheal noise measurement and qualitative scoring (0-3 scale) of ground-glass opacities, intralobular reticulations, bronchiectasis, bronchiolectasis, and honeycombing on 1 mm slices.
Results or Findings: The mean interval between scans was 33 ± 25 months. Despite higher image noise with PCCT-UHR (67.14 ± 13.18 HU vs 33.63 ± 5.81 HU; P < 0.0001), overall image quality was subjectively superior (P = 0.0348). PCCT-UHR yielded significantly improved visualization of ground-glass opacities (P = 0.0003), intralobular reticulations (P = 0.0045), bronchiectasis (P = 0.0001), and bronchiolectasis (P = 0.0002), with no significant difference for honeycombing (P = 0.125). Radiation dose was significantly lower with PCCT-UHR (CTDIvol: 2.35 ± 0.82 mGy; DLP: 77.64 ± 25.38 mGy·cm) compared to HRCT (CTDIvol: 3.35 ± 1.01 mGy; DLP: 116.77 ± 33.45 mGy·cm; P = 0.0008).
Conclusion: Ultra-high-resolution PCCT enables more accurate and lower-dose detection of early fibrotic changes in systemic sclerosis-related ILD, potentially improving disease monitoring and therapeutic decision-making.
Limitations: Monocentric retrospective study
Funding for this study: None
Has your study been approved by an ethics committee? Yes
Ethics committee - additional information: Waiver of informed consent

Author Block: X. Yang, J. Gao; Zhengzhou/CN
Purpose: To assess the diagnostic quality of chest CT images acquired using a photon-counting detector CT (PCD-CT) with quadruple-lows protocol (low radiation dose, injection rate, volume, and concentration of agent) in patients with lung cancer.
Methods or Background: This prospective study included patients with lung cancer undergoing PCD-CT and those undergoing energy-integrating detector CT (EID-CT)between July and September 2024. Participants, who were matched in terms of age, sex, and body mass index, underwent PCD-CT (quadruple-lows protocol: 2.0 mL/s injection rate, 1.0 mL/kg of 320 mg iodine/mL) and EID-CT(conventional protocol: 3.0 mL/s, 1.2 mL/kg of 350 mg iodine/mL). Radiation doses and renal function were recorded. Two radiologists independently evaluated the subjective image quality and lesion imaging features (lobulation, spiculation, pleural retraction, vacuole, and vessel convergence). The lesion and parenchymal metrics (signal-to-noise ratio[SNR], and contrast-to-noise ratio[CNR]) were assessed via quantitative analysis. Statistical data were compared using t-test and Mann–Whitney U test.
Results or Findings: Among 240 participants (mean age, 61.0±9.6; males, 65%), PCD-CT with the quadruple-lows protocol reduced the radiation dose by 55.1%(effective dose: 3.5±0.9 vs. 7.8±2.0 mSv; P < 0.001) while lowering contrast agent injection rate, volume, and concentration by 33.3%, 20.9%, and 8.6%, respectively, and reducing contrast-induced nephropathy(CIN)incidence by 5% compared with EID-CT. PCD-CT also exhibited significantly higher objective SNR and CNR in lung lesions and parenchyma across all scanned phases (P < 0.001), with superior subjective image quality scores(P < 0.001) and increased diagnostic confidence for all lung cancer imaging features(P < 0.05).
Conclusion: PCD-CT with the quadruple-lows protocol can significantly reduce the radiation dose, contrast agent usage, and CIN incidence while enhancing image quality and diagnostic confidence in lung cancer imaging features.
Limitations: Single-center study included a Chinese population, which may limit the generalizability of the results.
Funding for this study: None
Has your study been approved by an ethics committee? Yes
Ethics committee - additional information: The Ethics Committee of Biomedicine Research of the First Affiliated Hospital of Zhengzhou University

Author Block: K. Xu, Z. Zhu, L. Song; Beijing/CN
Purpose: To evaluate whether low-dose photon-counting CT (PCD-CT) can preserve the detection of key pulmonary abnormalities related to interstitial lung disease (ILD) while reducing radiation exposure, and to explore the incremental value of thinner-slice low-dose images.
Methods or Background: We prospectively enrolled patients with inflammatory myopathy–associated ILD patients(IM-ILD) who underwent same-day standard-dose (SD) PCD-CT and low-dose (LD) PCD-CT between October 2023 and November 2024. Four image series—SD-1.0 mm and LD-1.0 mm/0.4 mm/0.2 mm—were assessed for subjective image quality, noise, and visualization of normal structures using a 5-point Likert scale. Subsequently, two thoracic radiologists further evaluated the presence and confidence of ILD-related findings, including ground-glass opacity with reticulation (GG+R), ground-glass opacity with traction bronchiectasis (GG+B), and honeycombing.
Results or Findings: Fifty patients were included (mean age 53 ± 11 years; 9 males). The mean effective dose was significantly lower for LD vs SD (0.32 ± 0.07 mSv vs 2.25 ± 0.56 mSv; p < 0.001). Although SD showed better results than LD in overall image quality and image noise (p < 0.05), detection rates for GG+R, GG+B, consolidation, and honeycombing showed no significant differences across the four series, except for GG+B between SD-1 mm and LD-0.2 mm. Reader confidence was also comparable, except for lower confidence in GG+B on LD-0.2 mm. Thinner LD-0.4 mm images provided incremental detection in a small number of cases of GG+B missed on 1 mm images, whereas LD-0.2 mm showed no added benefit.
Conclusion: Low-dose PCD-CT substantially reduced radiation exposure while still providing good capability in detecting ILD-related pulmonary abnormalities compared with standard-dose PCD-CT, with thinner slices offering additional diagnostic value.
Limitations: The sample size was relatively small.
Funding for this study: This study has received funding from the National Natural Science Foundation of China (NSFC no. 82171934) and the National High-Level Hospital Clinical Research Funding (2022-PUMCH-B-069).
Has your study been approved by an ethics committee? Yes
Ethics committee - additional information: The Institutional Review Board of our hospital approved this prospective study [I-23PJ1459].

Author Block: J. Happe¹, C. Bruni², L. Jungblut¹, N. Landini³, C. Blüthgen¹, A. R. Larici³, T. Frauenfelder¹, O. Distler², J. Kroschke¹; ¹Zürich/CH, ²Zurich/CH, ³Rome/IT
Purpose: To investigate whether the superior image quality of photon-counting detector CT (PCD-CT)
facilitates the application of automated lung texture analysis (LTA) for detecting interstitial
lung disease (ILD) in systemic sclerosis (SSc) compared to conventional energy-integrating
detector CT (EID-CT).
Methods or Background: 186 patients with systemic sclerosis (SSc), who had
undergone clinically indicated EID-CT or PCD-CT, were included. Matching was performed
based on comparable demographical and rheumatological profiles to ensure comparability.
Visual ILD assessment by three expert radiologists served as the reference standard. Image
quality was assessed both subjectively using Likert-scales and objectively by measuring
signal-to-noise ratios (SNR). Quantitative ILD features and disease extent were extracted
using LTA based on the CALIPER algorithm (Imbio). Diagnostic accuracy was evaluated
through ROC-AUC analysis.
Results or Findings: LTA-based ILD-assessment showed higher AUC for PCD-CT than EID-CT in detecting ILD
(PCD-CT AUC: 0.846 vs. EID-CT AUC: 0.772) and specific ILD features, including groundglass
opacities, reticulation, and honeycombing. However, EID-CT showed higher AUCs
than PCD-CT in detecting extensive ILD (>20% lung involvement; AUC = 0.978 vs. 0.842).
Despite reduced radiation exposure, PCD-CT still delivered comparable SNR alongside
improved image quality rating scores.
Conclusion: LTA demonstrated acceptable to excellent AUC values for ILD detection on both, PCD-CT
and EID-CT scans, with PCD-CT-based LTA consistently achieving superior AUCs in
detecting individual ILD features in systemic sclerosis. Notably, LTA models trained on EIDCT
data performed robustly when applied to PCD-CT images. Accordingly, the improved
image quality and reduced radiation dose of PCD-CT support its potential for longitudinal ILD
monitoring using LTA. Nonetheless, further multicenter validation is necessary to confirm
these findings.
Limitations: Post-hoc-analysis with the use of visual assessment by experienced thoracic
radiologists as the reference standard for LTA-derived parameters, due to the lack of
pathological confirmation.
Funding for this study: No funding was provided for this study.
Has your study been approved by an ethics committee? Yes
Ethics committee - additional information: The ethics committee notification can be found
under the number BASEC 2018-02165.

Author Block: M. Zhang, B. Kun, L. Zhifei, H. K. Zhang, J. Shen, K. Liang; Shanghai/CN
Purpose: To compare the image quality and diagnostic performance of photon-counting detector CT (PCCT) with energy-integrating detector CT (EID-CT) for pulmonary nodule diagnosis by using both radiologist assessment and computer-assisted diagnosis (CAD).
Methods or Background: Thirty-four patients were retrospectively included (EID-CT, n=17; PCCT, n=17). All chest CTs were acquired at 120 kVp with automatic tube current modulation. Both EID-CT and PCCT images were reconstructed using hybrid iterative reconstruction (HIR) with 512×512 and 1024×1024 matrices. A radiologist recorded radiation dose and evaluated image quality using a five-point scale (1=non-diagnostic, 5=excellent). Solid (SN), ground-glass (GGN), and part-solid (PSN) nodules were independently identified by both a radiologist and CAD. Nodule detection performance was evaluated across the four image groups, using a blinded senior radiologist’s assessment of all available reconstructions served as the reference standard.
Results or Findings: There were no significant differences in baseline characteristics (gender, age, BMI) or nodule distribution between the groups (P>0.05). The effective radiation dose with PCCT was 70.2% lower than with EID-CT (2.94±0.49 vs. 9.85±1.13mSv; p<0.05). PCCT (HIR, 1024×1024) achieved the highest subjective image quality, significantly outperforming the best-performing EID-CT at the same matrix size (4.82±0.39 vs. 3.88 ± 0.49, p<0.05). For all three nodule types, PCCT outperformed the best-performing EID-CT (HIR, 1024×1024) for both the radiologist and CAD. Radiologist detection rates on PCCT were 88.1%(37/42), 92.3%(12/13), and 100%(2/2) for SN, GGN, and PSN, respectively; CAD on PCCT achieved 100.0% across all subtypes, versus 75.4%(43/57), 77.8%(14/18), and 50.0%(1/2) for the radiologist and 64.9%(37/57), 100.0%(18/18), and 50.0%(1/2) for CAD on EID-CT.
Conclusion: PCCT provides higher spatial resolution and lower radiation dose, as confirmed by both radiologist evaluation and automated detection software, supporting its clinical value for pulmonary nodule detection.
Limitations: Small sample size; limited number of part-solid nodules.
Funding for this study: N/A
Has your study been approved by an ethics committee? Yes
Ethics committee - additional information: The study protocol was approved by the Institutional Review Board.

Author Block: M. Moeskes¹, T. Derlin², A. M. Hunkemöller¹, C. M. Schaefer-Prokop³, J. Eckstein¹, B. C. Meyer¹, J. Vogel-Claussen¹, F. Wacker¹, H-o. Shin¹; ¹Hannover/DE, ²Bad Oeynhausen/DE, ³Amersfoort/NL
Purpose: The purpose of this study was to compare quantitative lung perfusion assessment using photon-counting computed tomography (PCCT) with ventilation/perfusion single-photon emission computed tomography (V/Q-SPECT), the current reference standard, in patients with suspected or confirmed chronic thromboembolic pulmonary hypertension (CTEPH).
Methods or Background: This retrospective, single-centre study included twenty-three patients (13 men, ten women; mean age 67.9 ± 10.7 years) who underwent both PCCT and V/Q-SPECT between 01.10.2021 and 31.12.2024. Lobar and whole-lung perfusion were quantified using PCCT-derived perfused blood volume maps and V/Q-SPECT perfusion images. Lung and lobe segmentation was performed with an artificial intelligence-based tool. Perfusion values were normalised (95% confidence interval z-score scaling). Agreement between modalities was analysed with Pearson correlation and Bland–Altman analysis, and perfusion defect volumes were compared across thresholds.
Results or Findings: Whole-lung mean perfusion correlated strongly between PCCT and V/Q-SPECT (r = 0.72, p < 0.05). Lobar correlations ranged from r = 0.62 in the middle lobe to r = 0.85 in the left lower lobe. PCCT yielded slightly higher mean perfusion values (0.50 ± 0.04) compared to V/Q-SPECT (0.49 ± 0.09). Bland–Altman analysis showed a bias of +0.015 with limits of agreement from –0.13 to +0.16. Perfusion defect volume correlation was moderate, with whole-lung r = 0.60 and lobar r = 0.49–0.77. Image quality was affected by venous contrast artefacts in PCCT and respiratory misregistration in V/Q-SPECT.
Conclusion: PCCT-based perfusion imaging demonstrates high concordance with V/Q-SPECT, supporting its potential as a comprehensive single-modality approach for functional and anatomical evaluation of CTEPH.
Limitations: The limitations of the study are its single-centre, retrospective design and the relatively small sample size.
Funding for this study: No funding was received for this study.
Has your study been approved by an ethics committee? Yes
Ethics committee - additional information: All individuals provided written informed consent, and the requirement for ethics approval was
waived by the institutional review board (No. 10724_BO_K_2023).

Author Block: M-J. Sähn, E. Topal, J. Ottemöller, R. I. Danebrock, J. Borggrefe, A. S. Surov; Minden/DE
Purpose: Photon counting computed tomography (PCCT) is a novel imaging modality able to measures iodine concentration within tumors. However, correlations between iodine concentration and histopathological features are not well established in lung cancer. This study aims to adress the issue.
Methods or Background: NSCLC (adenocarcinoma, squamous cell carcinoma) cases were evaluated using standardized protocols for measuring normalized iodine concentration (NIC) in PCCT and correlated it with Ki67 proliferation rate, number of tumor cells per unit area („cell count“), tumor proportion score (TPS), combined positive score (CPS), and immune cell (IC) score. SCLC NIC was correlated with Ki67 proliferation rate. All NICs were tested for subtype differences via Wilcoxon test. Interobserver reliability was assessed using intraclass correlation coefficients (ICCs).
Results or Findings: A total of 92 cases (NSCLC n=58, SCLC n=34) were included. The ICCs showed excellent inter-observer consistency for iodine concentration measurements in both NSCLC and small-cell lung cancer (SCLC). Correlation analysis revealed no significant association between iodine concentration and Ki67 proliferation rate, TPS, CPS, IC score or cell count in most tumor subtypes. However, a weak, statistically siginificant positive correlation was found with TPS in adenocarcinoma (0.21, p=0.007). No significant difference in iodine concentration between lung cancer subtypes was observed.
Conclusion: Our study demonstrates excellent interobserver consistency for measuring iodine concentration using PCCT in NSCLC and SCLC. While limited correlation with histopathological features was observed, the results suggest that iodine concentration may be useful to predict TPS in adenocarcinoma.
Limitations: Retrospective study.
Funding for this study: None.
Has your study been approved by an ethics committee? Yes
Ethics committee - additional information: Ruhr-University Bochum (2021–827)

Author Block: Y. y. Wang, H. Wu, Y. Wang, X. Yu; Shanghai/CN
Purpose: To investigate the added value of multiparametric dual energy CT (DECT) radiomics integrated with clinical-radiological features for noninvasive differentiation of benign and malignant solid pulmonary nodules (SPNs), with emphasis on external validation and diagnostic performance in sub-centimeter nodules.
Methods or Background: This retrospective study enrolled 441 patients with pathologically confirmed SPNs who underwent preoperative DECT ( IQon CT and CT7500, Philips Healthcare), divided into training (n=252), internal test (n=112), and external test (n=77) cohorts. Radiomics features were extracted from conventional and virtual monoenergetic images (40 and 70 keV), and material decomposition images (including iodine density (ID), Z-effective atomic number (Zeff), electron density (ED) maps) in arterial (AP) and venous phases (VP). Logistic regression constructed radiomics models, and combined clinical-radiomics model was visualized as a nomogram. Subgroup analysis was performed by nodule size (≤10 mm vs >10 mm), and diagnostic accuracy was compared with that of two radiologists.
Results or Findings: A total of 441 SPNs (112 benign, 329 malignant) were included. The optimal radiomics model, comprising features from ID in VP and Zeff in both AP and VP, achieved area under the curve (AUC) of 0.835, 0.804, and 0.772 in the training, internal, and external cohorts, respectively. The combined model (age, lobulation, and 10 radiomic features) outperformed the clinical-radiological model in all cohorts (AUC: 0.889 vs 0.816; 0.865 vs 0.795; 0.823 vs 0.742; p<0.05). It maintained strong performance for ≤10 mm and >10 mm nodules, with AUC of 0.875 and 0.888 (internal test) and 1.000 and 0.794 (external test).
Conclusion: A DECT-based multiparametric radiomics model integrated with clinical radiological features enables accurate and noninvasive differentiation between benign and malignant SPNs, including sub-centimeter nodules.
Limitations: Retrospective design may introduce selection bias.
Funding for this study: National Key Research and Development Program of China (No. 2024YFF0728600)
Has your study been approved by an ethics committee? Yes
Ethics committee - additional information: Approved by the institutional review board of Renji Hospital affiliated to Shanghai Jiao Tong University (approval number: LY2025-036-B) and Sun Yat-sen University Cancer Center (approval number: B2025-189-01).

Author Block: A. Al-Jabir, C. Ridge, T. R. Semple; London/UK
Purpose: To evaluate radiation dose in CT pulmonary angiography (CTPA) on photon-counting CT (PCCT) versus energy-integrating CT (EID), combining meta-analysis with institutional data stratified by BMI.
Methods or Background: A systematic review of MEDLINE and Embase identified studies reporting dose metrics for PCCT and EID-CT. A random-effect model was used for pooled mean differences.

At our institution, consecutive CTPA data was analysed from a PCCT scanner (NAEOTOM Alpha; n=44) and a dual-source EID scanner (SOMATOM Force; n=565). Dose-length product (DLP) was extracted from diagnostic chest series only, and patients were stratified by WHO body mass index (BMI) categories.
Results or Findings: Meta-analysis review of four institutional series (n = 372) confirmed significantly lower doses with PCCT (pooled mean DLP: 113 vs 156 mGy·cm (SMD: −0.70, 95% CI −1.18 to −0.23, p = 0.004), although highly heterogeneous (I² = 82%).

In our institutional experience, both delivered doses within accepted DRLs across BMI groups.
Median DLP was modestly lower with PCCT (110, IQR 45.7) than EID (122, IQR 98.6; p=0.256), with the difference most pronounced in obese patients (156 [IQR 54, n=7] vs 193 [IQR 121.8, n=113]; p=0.054).

Elevated BMI remained the main driver of dose, with both systems showing greater variability at extremes of weight; outliers disproportionately inflated means. Both scanners possess high tube power, enabling excellent image quality but also risking higher exposures at extremes of weight if protocols are not carefully adapted.
Conclusion: Both PCCT and EID systems delivered radiation doses that remained well within acceptable limits across all BMI categories.
PCCT trended toward dose reductions, most evident in obese patients.
However, high BMI continues to challenge dose efficiency; with both systems offering substantial tube power, real-world benefit depends on BMI-adapted protocol optimisation.
Limitations: No limitations were identified.
Funding for this study: No funding was received for this study.
Has your study been approved by an ethics committee? Not applicable
Ethics committee - additional information:

Author Block: L. Piscopo¹, G. Rea², A. G. Fois¹, D. Turilli¹, G. De Paula¹, L. M. Fattacciu¹, E. Solinas¹, S. Masala¹, M. Scaglione¹; ¹Sassari/IT, ²Napoli/IT
Purpose: Sarcoidosis is a multisystem granulomatous disease, and the lung is the most commonly affected organ. The aim of this prospective study was to assess the morphological performance of Photon-counting CT (PCCT), with dual reconstruction kernel (HR and soft tissue kernels) in patients with pulmonary sarcoidosis, focusing on its diagnostic accuracy, radiation dose reduction, ultra-high-resolution (UHR) and spectral capabilities.
Methods or Background: Forty consecutive patients with pulmonary sarcoidosis underwent PCCT at our institution. Two chest radiologists blinded the imaging reports and functional data. Detailed evaluation of the granulomatous alterations with HRCT imaging (nodular, ground glass opacity, consolidative reticular, fibrosing) was the object of the radiological evaluation with the further aim of identifying elements of sub-millimetric detail (intercepted excellently by the PCCT) that could increase the diagnostic power. Radiation dose indices (CTDIvol, DLP, effective dose) were compared with standard energy-integrating detector CT (EID-CT).
Results or Findings: PCCT with its iterative algorithm reconstruction and UHR protocols (0.4 mm, with select reconstructions at 0.2 mm), provided a sharper depiction of parenchymal microstructures, interlobular septa, nodules, fibrotic changes, and pleural abnormalities. Compared to EID-CT, PCCT significantly enhanced the diagnostic accuracy with great potential in predictive value, while the radiation dose analysis demonstrated a 30–50% reduction in CTDIvol and effective dose.
Conclusion: PCCT provides significant advantages in granulomatous disorders, particularly in pulmonary sarcoidosis. Its UHR morphological detail, using 0.25 mm isotropic voxels, facilitates clear visualization of tiny micronodules near 0.5 mm and subtle early fibrotic reticulations in order to reduce the radiant load, expand spectral/quantitative potential, and improve its diagnostic accuracy and positive predictive value. Therefore, PCCT could improve the staging, therapy monitoring, and future integration into precision imaging pathways for granulomatosis lung diseases.
Limitations: Lack of standardization for new imaging method technology.
Funding for this study: This research received no external funding
Has your study been approved by an ethics committee? Yes
Ethics committee - additional information: The study was conducted according to the guidelines of
the Declaration of Helsinki. The local Institutional review board approved the study. The Ethical
Committee’s approval was obtained (2022030).

Author Block: X. Tong¹, J. Sun¹, J. Zhou¹, Y. Li², M. Jiang³, L. JIE¹, B. Li³, X. Liang²; ¹Chengdu/CN, ²ShangHai/CN, ³ShenYang/CN
Purpose: To analyze the image quality and diagnostic performance of high-resolution ultra-low-dose photon-counting CT (PCCT) in evaluating lung nodules with varying sizes and densities, and perform a comparative analysis with standard-dose energy-integrating detector CT (EID-CT). The ultimate goal is to verify the superiority of high-resolution ultra-low-dose PCCT in lung nodule imaging and its potential for clinical application.
Methods or Background: Fifteen spherical nodules, covering five diameters (3 mm, 5 mm, 8 mm, 10 mm, 12 mm) and three density levels (100 HU, -630 HU, -800 HU), were randomly embedded in a commercial lung phantom and scanned. High-resolution low-dose scanning was performed using PCCT (NeuViz P10); while standard-dose scanning was conducted with EID-CT (NeuViz Epoch+). Lung nodules were automatically detected using CAD software and subsequently evaluated in terms of contrast-to-noise ratio (CNR). Differences among scanning protocols were assessed using repeated measures ANOVA.
Results or Findings: The effective dose of PCCT was 0.524 mSv, compared with 2.425 mSv for EID-CT, corresponding to an approximately 78.4% reduction in radiation dose. For data reconstructed at 512 matrix size, PCCT showed higher CNR than EID-CT at both 512 (t = 4.812, p = 0.001) and 1024 (t = 4.743, p = 0.001) matrix sizes. Similarly, for data reconstructed at 1024 matrix size, PCCT showed higher CNR than EID-CT at both 512 (t = 3.691, p = 0.006) and 1024 (t = 3.166, p = 0.013) matrix sizes.
Conclusion: Despite approach 80% decrease in radiation dose, PCCT remains superior to large-matrix EID-CT when evaluating lung nodules and overall image quality, This finding strongly indicates that PCCT holds great potential as a reliable substitute for standard-dose EID-CT in applications like lung nodule assessment.
Limitations: These findings require further validation across diverse parameter settings and in vivo.
Funding for this study: No funding was received for this study.
Has your study been approved by an ethics committee? Not applicable
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