Photon-counting CT for hepato-bilio-pancreatic imaging: a qualitative head-to-head comparison with third-generation dual-source CT: preliminary results.

Feasibility of low concentration iodinated contrast medium in portal venous abdominal imaging: performance of photon-counting CT virtual monoenergetic imaging compared to conventional EID-CT.

PURPOSE To evaluate whether reduced-iodine photon-counting CT (RI-PCCT) virtual monoenergetic imaging (VMI) provides comparable quantitative and non-inferior qualitative image quality compared with standard-iodine energy-integrating detector CT (SI-EIDCT) in portal venous phase abdominal imaging, and to identify the optimal keV range. MATERIALS AND METHODS This retrospective study included 84 adult patients who underwent abdominopelvic PCCT using a lower-concentration iodinated contrast medium (270 mg I/mL) administered at the same injection volume as routine practice, resulting in a reduced total iodine dose, and who had a prior conventional EID-CT performed with standard contrast medium (350 mg I/mL) within one year. Organ-specific contrast-to-noise ratio (CNR) and signal-to-noise ratio (SNR) were calculated across virtual monoenergetic imaging (VMI) levels ranging from 40 to 65 keV and compared with EID-CT. Two independent radiologists assessed subjective image quality at predefined VMI levels (40, 45, and 50 keV) using a 5-point Likert scale. Non-inferiority testing was performed using a predefined margin of -0.5. RESULTS The total iodine dose was significantly lower in the PCCT group than in the EID-CT group (400.60 ± 29.82 vs. 517.88 ± 39.46 mgI/kg, P < 0.001). At 40 keV, RI-PCCT demonstrated higher CNR than SI-EIDCT for the pancreas, portal vein, and spleen (all P < 0.001), whereas liver CNR was similar. SNR showed organ-specific reductions, particularly in the liver. Qualitative scores were lower at 40 keV, but 45 keV and 50 keV met the predefined non-inferiority criterion for all qualitative parameters using a -0.5-point margin. Interobserver agreement was excellent for all qualitative parameters (Gwet's AC2, 0.932-0.975). CONCLUSIONS RI-PCCT provided comparable quantitative and non-inferior qualitative image quality compared with SI-EIDCT, while lowering the iodine and radiation dose. VMI at 45-50 keV provided the optimal balance of contrast and noise, supporting its potential clinical feasibility for routine portal venous phase imaging.

Clinical Photon-Counting CT in Neuroradiology: A Real-World Paired Comparison with Conventional Energy-Integrating CT.

BACKGROUND AND PURPOSE Photon-counting CT offers higher spatial resolution, improved contrast-to-noise efficiency, and spectral imaging, but its performance against heterogeneous EID-CT systems in routine use remains incompletely characterized. We compared image quality, pathology conspicuity, and radiation dose between clinical PCCT and EID-CT in paired routine neuroradiological examinations, accounting for differences in scanner generation, protocol, and reconstruction. We hypothesized higher image-quality and pathology-conspicuity scores and dose efficiency, while treating the comparison as pragmatic rather than detector-isolating. MATERIALS AND METHODS This retrospective study included consecutive adults undergoing routine clinical PCCT from December 2023 through February 2024 who had a corresponding same-region EID-CT within three months; when several EID-CT scans were eligible, the closest in time was selected. Examinations were grouped by protocol: non-contrast brain CT was the primary cohort; contrast-enhanced brain CT and arterial and venous CTA were exploratory. Four blinded readers assessed image quality and pathology conspicuity, with paired scans assigned to separate sessions at least four weeks apart. CNR, dose-normalized CNR (CNRD), and radiation dose were compared within subjects using the Wilcoxon signed-rank test. RESULTS The 194 patients (mean age, 65±15 years; 100 males) contributed to 270 pairs: 225 non-contrast brain CTs, 14 contrast-enhanced brain CTs, 26 arterial CTAs, and 5 venous CTAs. In the primary cohort, PCCT was associated with higher overall image-quality scores (median 4 versus 3; p<.001), higher time-independent pathology conspicuity in 224/225 pairs (median 4 versus 3; p<.001), 102%-152% higher GM/WM CNR, 128%-180% higher CNRD, and 22% lower median dose (38.4 versus 49.2 mGy; all p<.001). All three primary endpoints remained significant in the ≤1-day subset (n=60). Artifact scores did not differ significantly. Exploratory contrast-enhanced and angiographic analyses favored PCCT for selected parenchymal and small-vessel metrics, including perforator visualization (median 3 versus 2; p<.001), but these small subgroups were preliminary and did not strengthen the primary conclusions. CONCLUSIONS PCCT was associated with higher image quality, pathology conspicuity, GM/WM CNR and CNRD, and lower dose in routine non-contrast brain CT. Smaller protocol groups were exploratory. Because scanner generations, vendors, protocols, and reconstructions were unmatched, the differences cannot be attributed solely to detector technology.

Single-Phase Surrogate for True Non-Contrast Liver CT Using 190-keV Monoenergetic Imaging on Photon-Counting CT: Implications for Hepatic Steatosis Assessment.

RATIONALE AND OBJECTIVES To evaluate whether 190-keV virtual monoenergetic imaging (VMI) using photon-counting detector CT (PCD-CT) can serve as a surrogate for true non-contrast (TNC) in hepatic steatosis quantification and to compare its attenuation agreement with virtual non-contrast (VNC). METHODS Forty-nine patients who underwent abdominal PCD-CT and MRI-proton density fat fraction (PDFF) within 2 months were retrospectively analyzed. VNC and 190-keV VMI were reconstructed from equilibrium-phase scans. Liver attenuation was measured on TNC, VNC, and 190-keV VMI in four hepatic segments. Pearson correlation and Bland-Altman analyses assessed agreement with TNC. Receiver operating characteristic analysis evaluated diagnostic performance for steatosis (MRI-PDFF ≥ 5%). Statistical analyses were performed using MedCalc (version 23.4) and GraphPad Prism (version 10.6.1). Statistical significance was defined as p < 0.05. RESULTS The study included 49 patients (30 men, 19 women; mean age, 66.7 ± 11.2 years). In whole-liver analysis, 190-keV VMI correlated strongly with TNC (r=0.921, p<0.001), comparable to VNC (r=0.925). In the anterior segment, VNC showed a larger positive bias relative to TNC (+5.5 HU), whereas 190-keV VMI showed a smaller bias (+2.2 HU) that more accurately reproduced the regional attenuation pattern. For detecting steatosis in the anterior segment, a significant difference in area under the curve was observed between TNC and VNC (0.921 vs 0.817, p=0.018), whereas no significant difference was found between TNC and 190-keV VMI (0.921 vs 0.869, p=0.149). CONCLUSION 190-keV VMI may serve as a practical surrogate for TNC in hepatic steatosis quantification, demonstrating reduced segment-dependent bias compared with VNC in artifact-prone regions.

Photon-counting detector CT for CT pulmonary angiography: a systematic review and meta-analysis.

Detection of hypodense hepatic and renal lesions on abdominal CT reconstructed with deep learning image reconstruction technique in patients with large body habitus: A multi-reader study.

In patients with large body habitus, DLIR-M and -H improved IQ and CNR with DLIR-H providing superior lesion conspicuity and diagnostic confidence; this study represents one of the first evaluations of DLIR performance in this specific patient population.

Ultra-High-Resolution Dual-Source Photon-Counting CT for Expanded Characterization of Pathophysiological Imaging Patterns in Multiple Myeloma.

RATIONALE AND OBJECTIVES Dual-source photon-counting CT (DS-PCCT) combines spectral imaging with ultra-high spatial resolution for whole-body assessment of multiple myeloma (MM). This study assessed axial and appendicular skeletal manifestations at initial diagnosis by exploiting attenuation characteristics of soft tissue and fat in low-keV virtual monoenergetic images (VMI). MATERIALS AND METHODS In this retrospective study, 84 patients (67.1±10.5 y, 54 men) underwent whole-body DS-PCCT between November 2024 and December 2025. The sample comprised 53 therapy-naïve MM patients and 31 with precursor conditions (monoclonal gammopathy of undetermined significance, smoldering myeloma, solitary plasmacytoma). Three board-certified radiologists measured CT attenuation of osteolytic lesions and femoral bone marrow at 70 and 40 keV. Long bones were evaluated for diffuse high-grade, nodular, pseudonodular, and fatty marrow patterns, as well as endosteal scalloping. RESULTS Among 53 MM patients, 40 (75.5%) spectral-morphologic analysis identified 3 patient-level imaging phenotypes of osteolytic bone disease: a soft-tissue-attenuation phenotype (n=25, 47.2%), a fat-attenuation phenotype (n=10, 18.9%), and coexistence of both lesion types (n=5, 9.4%). The pseudonodular pattern was the predominant femoral marrow imaging pattern, whereas fatty marrow (30.2%), nodular lesions (18.9%), and diffuse high-grade infiltration (3.8%) occurred less frequently. Endosteal scalloping occurred exclusively in osteolytic MM (18.9%). Precursor conditions mainly showed fatty (58.1%) and pseudonodular (38.7%) patterns. Low-keV VMI demonstrated distinct energy-dependent attenuation across patterns. Inter-reader agreement for Hounsfield unit measurements was good to excellent (ICC >0.82). CONCLUSIONS DS-PCCT identified a previously undescribed fat-attenuation-predominant imaging phenotype in MM that meets criteria for symptomatic bone disease but is not captured by current International Myeloma Working Group definitions of focal lesions. Spectral-morphologic characterization of marrow involvement may complement existing imaging criteria and aid differentiation between overt MM and nonspecific marrow abnormalities.