Photon-Counting CT With Low-keV Virtual Monoenergetic Images for Detecting Muscle Invasion in Bladder Cancer: A Prospective Study.

Electron Density Dual-Energy CT for Liver Metastasis Detection Compared with Conventional and Virtual Monoenergetic Images at 40 keV.

OBJECTIVE To estimate the contrast-to-noise ratio (CNR) of liver metastases with electron density (ED) derived from dual-energy computed tomography and compare it with conventional and virtual monoenergetic images at 40 keV in both the unenhanced and portal-dominant phases. METHODS This observational retrospective, single-institution study included 32 patients with 49 liver metastases originating from digestive adenocarcinoma. All patients underwent dual-energy computed tomography (Spectral IQON®, Philips Healthcare) during unenhanced and portal-dominant phases. Conventional, virtual monoenergetic (VMI) images at 40 keV and ED images were reconstructed. The CNR of each metastasis was measured for each reconstruction in both the unenhanced and portal-dominant phases. Comparisons between techniques were conducted using linear mixed model regression. RESULTS Forty-nine liver metastases were included. For unenhanced acquisitions, ED demonstrated a statistically significantly higher CNR than both VMIs at 40 keV (mean difference 12.56 [95% IC, 10.17 to 14.95], p < 0.001) and conventional reconstructions (mean difference 12.83 [95% IC, 10.44 to 15.55], p < 0.001). Similarly, in the portal venous phase, ED showed a significantly higher CNR compared with both 40 keV monoenergetic (mean difference 9.81 [95% IC, 7.42 to 12.20], p < 0.001) and conventional reconstructions (mean difference 16.62 [95% IC, 14.23 to 19.00], p < 0.001). Moreover, a significantly better CNR was observed between unenhanced ED and portal venous 40 keV VMI (14.4626 ± 7.5 vs 11.1810 ± 6.2, respectively; p = 0.007). DISCUSSION Few studies have investigated electron density. These findings suggest that the CNR of liver metastases with ED is better than conventional and VMIs at 40 keV reconstructions, in both the unenhanced and portal-dominant phases. The single-center design and the small sample size limit the generalizability of these results. CONCLUSION Electron density provides a significantly better CNR for liver metastasis compared with both conventional and VMI at 40 keV reconstructions. Further studies are required to demonstrate that this gain in CNR improves the detection of hepatic metastases.

Image-quality optimization for late iodine enhancement with photon-counting CT: impact of spectral analysis and reconstruction parameters.

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.

Ultra-low dose chest-abdomen-pelvis CT with deep-learning image reconstruction for cancer follow-up: Impact on image quality and lesion detection.

PURPOSE The purpose of this study was to compare the image quality and lesion detection between ultra-low dose (ULD) chest-abdomen-pelvis computed tomography (CAP-CT) reconstructed with a deep-learning image reconstruction (DLR) algorithm, and standard-dose CT (STD-CT) in cancer follow-up. MATERIALS AND METHODS A total of 106 patients undergoing CAP-CT for the follow-up of cancer were prospectively included. Each patient underwent both STD-CT and ULD-CT acquisitions. ULD-CT images were reconstructed using two DLR levels (Smooth/Smoother). Dosimetric indicators, objective image quality, subjective image quality, and lesion detection were compared. Agreement between protocols and readers was assessed using Gwet's AC1 or AC2 coefficients. RESULTS ULD-CT significantly reduced radiation exposure, with a mean CTDIvol reduction of -71.5% and dose-length product reduction of -71.5% (P < 0.05). Minor but statistically significant differences in HU values were observed between STD-CT and ULD-CT across most tissues. For all organs or tissues, image noise was significantly higher with ULD-CT-Smooth than with STD-CT (P < 0.001), and with ULD-CT-Smoother than with STD-CT, except for dorsal vertebra (P = 0.39) and trachea (P = 0.26). For all organs or tissues, image noise was significantly lower with the Smoother DLR level than with Smooth DLR level (P < 0.001). Agreement between STD-CT and ULD-CT regarding lesion detection was almost perfect for thoracic, abdominal, and bone lesions. Detection of infracentimetric hepatic was lower with ULD-CT, whereas detection of larger lesions (≥ 10 mm) remained similar. Subjective image quality was lower with ULD-CT, with moderate inter-reader agreement, and lower diagnostic confidence than with STD-CT. One of the two readers considered that 19%-24% of ULD-CT examinations were uninterpretable. CONCLUSION ULD-CT with DLR offers substantial radiation dose reduction but resulted in poorer image quality and lower detection of small low-contrast abdominal lesions compared with STD-CT. Although lesion detection remained equivalent for thoracic and skeletal lesions, the high proportion of suboptimal or uninterpretable examinations may limit routine use of ULD protocols in cancer follow-up.

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.

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.