Objectives: The aim of this study is to improve the reliability of subjective IQ assessment using a pairwise comparison (PC) method instead of a Likert scale method in abdominal CT scans. Methods: Abdominal CT scans (single-center) were retrospectively selected between September 2019 and February 2020 in a prior study. Sample variance in IQ was obtained by adding artificial noise using dedicated reconstruction software, including reconstructions with filtered backprojection and varying iterative reconstruction strengths. Two datasets (each n = 50) were composed with either higher or lower IQ variation with the 25 original scans being part of both datasets. Using in-house developed software, six observers (five radiologists, one resident) rated both datasets via both the PC method (forcing observers to choose preferred scans out of pairs of scans resulting in a ranking) and a 5-point Likert scale. The PC method was optimized using a sorting algorithm to minimize necessary comparisons. The inter- and intraobserver agreements were assessed for both methods with the intraclass correlation coefficient (ICC). Results: Twenty-five patients (mean age 61 years ± 15.5; 56% men) were evaluated. The ICC for interobserver agreement for the high-variation dataset increased from 0.665 (95%CI 0.396–0.814) to 0.785 (95%CI 0.676–0.867) when the PC method was used instead of a Likert scale. For the low-variation dataset, the ICC increased from 0.276 (95%CI 0.034–0.500) to 0.562 (95%CI 0.337–0.729). Intraobserver agreement increased for four out of six observers. Conclusion: The PC method is more reliable for subjective IQ assessment indicated by improved inter- and intraobserver agreement. Clinical relevance statement: This study shows that the pairwise comparison method is a more reliable method for subjective image quality assessment. Improved reliability is of key importance for optimization studies, validation of automatic image quality assessment algorithms, and training of AI algorithms. Key Points: • Subjective assessment of diagnostic image quality via Likert scale has limited reliability. • A pairwise comparison method improves the inter- and intraobserver agreement. • The pairwise comparison method is more reliable for CT optimization studies. Graphical

This study aims to demonstrate reduced iodine contrast media (CM) in routine abdominal CT scans in portal venous phase (PVP) using a photon-counting detector CT (PCD-CT) compared to total body weight (TBW) and kV-adapted CM injection protocols on a state-of-the-art energy-integrating detector CT (EID-CT) while maintaining sufficient image quality (IQ). Consecutive contrast-enhanced abdominal PVP CT scans from an EID-CT (Nov 2022-March 2024) and a PCD-CT (Sep 2023-Dec 2023) were compared. CM parameters (total iodine load (TIL), iodine delivery rate (IDR) and dosing factor (DF)) were reported. An individualized acquisition and CM injection protocol based on TBW and kV was applied for the EID-CT and a TBW adapted CM injection protocol was used for the PCD-CT. Objective IQ was evaluated with mean attenuation (Hounsfield Units, HU), signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR)). Subjective IQ was assessed via a 5-point Likert scale by 2 expert readers based on diagnostic confidence. Based on 91 EID-CT scans and 102 PCD-CT scans a TIL reduction of 20.1 % was observed for PCD-CT. PCD-CT demonstrated significantly higher SNR (9.9 ± 1.7 vs. 9.1 ± 1.8, p < 0.001) and CNR (5.1 ± 1.7 vs. 4.3 ± 1.3, p < 0.001) compared to EID-CT. Subjective IQ assessment showed that all scans had sufficient diagnostic IQ. PCD-CT allows for CM reduction while providing higher SNR and CNR compared to EID-CT, using clinical individualized scan and CM injection protocols.

Objectives: Quantifying diagnostic image quality (IQ) is not straightforward but essential for optimizing the balance between IQ and radiation dose, and for ensuring consistent high-quality images in CT imaging. This review provides a comprehensive overview of advanced objective reference-free IQ assessment methods for CT scans, beyond standard approaches. Methods: A literature search was performed in PubMed and Web of Science up to June 2024 to identify studies using advanced objective image quality methods on clinical CT scans. Only reference-free methods, which do not require a predefined reference image, were included. Traditional methods relying on the standard deviation of the Hounsfield units, the signal-to-noise ratio or contrast-to-noise ratio, all within a manually selected region-of-interest, were excluded. Eligible results were categorized by IQ metric (i.e., noise, contrast, spatial resolution and other) and assessment method (manual, automated, and artificial intelligence (AI)-based). Results: Thirty-five studies were included that proposed or employed reference-free IQ methods, identifying 12 noise assessment methods, 4 contrast assessment methods, 14 spatial resolution assessment methods and 7 others, based on manual, automated or AI-based approaches. Conclusion: This review emphasizes the transition from manual to fully automated approaches for IQ assessment, including the potential of AI-based methods, and it provides a reference tool for researchers and radiologists who need to make a well-considered choice in how to evaluate IQ in CT imaging. Critical relevance statement: This review examines the challenge of quantifying diagnostic CT image quality, essential for optimization studies and ensuring consistent high-quality images, by providing an overview of objective reference-free diagnostic image quality assessment methods beyond standard methods. Key Points: Quantifying diagnostic CT image quality remains a key challenge. This review summarizes objective diagnostic image quality assessment techniques beyond standard metrics. A decision tree is provided to help select optimal image quality assessment techniques. Graphical

CT image quality is strongly influenced by the energy of the x-ray beam. The tube voltage (kV) determines a polyenergetic x-ray spectrum, which affects both image contrast and noise in conventional energy-integrating detector CT (EID-CT) imaging. In photon-counting detector CT (PCD-CT), spectral data sets are always available by default, and virtual monoenergetic images (VMI) can be reconstructed at any specific photon energy (keV). This enables radiologists to tailor energy selection to dedicated clinical tasks, achieving an optimal balance between contrast, noise, and radiation dose, and ultimately enhancing diagnostic confidence. This article educates the reader on the differences between polyenergetic and monoenergetic images to provide radiologists with practical insights into optimizing spectral imaging protocols and leveraging keV differences in routine clinical practice. Using an anthropomorphic phantom with iodine rods, differences in image quality, specifically image contrast and noise, are demonstrated between polyenergetic EID-CT and PCD-CT VMIs.

Background: Since 2011, the International Commission on Radiological Protection (ICRP) has recommended an annual eye lens dose limit of 20 mSv for radiation workers, averaged over 5 years, with no year exceeding 50 mSv. However, limited research has been conducted on dose rate conversion coefficients (DCCs) for direct contamination of the eye.Purpose: This study aimed to accurately determine DCCs for the eye lens and cornea for ocular contamination with radionuclides used in nuclear medicine.Methods: DCCs for 37 radionuclides used in nuclear medicine were determined using two different methods. Method 1 involved conducting Monte Carlo (MC) simulations of an ICRU cylinder to determine the absorbed dose at a depth of 3 mm resulting from a point source. The accuracy of this simulation approach was validated by experimental thermoluminescent dosimeter (TLD) measurements for ¹⁸F, ⁶⁸Ga, ^99mTc, and ¹⁷⁷Lu. In method 2, average DCCs were calculated for the eye lens (complete and radiosensitive parts) and the cornea for both a point source and thin surface contamination centered on the cornea using MC simulations on the adult mesh‐type reference computational phantom of the eye from the ICRP (MRCP).Results: DCCs determined from TLD measurements showed excellent agreement (deviations: +1.4%, +4.7%, −3.1%, and −2.5% for ¹⁸F, ⁶⁸Ga, ^99mTc, and ¹⁷⁷Lu, respectively) compared to MC simulations of the experimental set‐up. For the 37 radionuclides, DCCs of the complete eye‐lens for a point source ranged from 2.53 × 10⁻⁷ to 4.15 × 10⁻² mGy MBq⁻¹ s⁻¹ for the adult MRCPs, being substantially smaller compared to DCCs determined via MC simulations of a ICRU cylinder. In general, point source and surface contamination showed comparable DCCs for the eye lens. Radionuclides emitting low‐energy beta radiation or conversion electrons (e.g., ¹⁷⁷Lu, ^99mTc) showed low DCCs as the radiation does not penetrate to the depth of the eye lens, while radionuclides emitting high‐energy beta radiation (e.g., ⁹⁰Y) showed high DCCs. Overall, DCCs for the radiosensitive part of the eye lens were larger (up to a factor of 3) compared to the complete eye lens. DCCs for the cornea were larger than for the eye lens with a factor that strongly depended on the emitted radiation type. Especially alpha emitters (e.g., ²¹¹At, ²²³Ra) showed high DCCs for the cornea because of the short range of alpha radiation, leading to local maxima in the cornea and not reaching the eye lens.Conclusion: DCCs at a depth of 3 mm in an ICRU cylinder and adult MRCP DCCs for both the complete and sensitive parts of the eye lens and cornea were determined for 37 radionuclides having applications in nuclear medicine. These DCCs are highly useful in radiation safety assessments and radiation dose calculations in ocular contamination incidents.

Objective. In proton therapy, dual-energy computed tomography (DECT) has shown to improve proton range estimation and treatment planning, but it is not yet widely implemented clinically as technology differences may restrict application (e.g. field-of-view or temporal separation). Recently, photon-counting CT (PCCT) was introduced clinically. PCCT offers multi-energy CT imaging in a single scan and with low imaging dose options. Therefore, this study aimed to evaluate proton range differences between PCCT and DECT across varying anthropomorphic phantom sizes, tissue types, and imaging doses. Approach. Virtual monoenergetic images (70 and 180 keV) were generated from DECT (80/140 kVp) and PCCT (120 kVp) scans at three imaging doses (CTDI _vol,32cm : 5, 10, and 20 mGy) using a commercial head phantom and a 3D-printed abdomen phantom with exchangeable fat rings for varying dimensions. Proton therapy plans were created in RayStation (RaySearch laboratories) with varying proton beam configurations (e.g. crossing different tissues) to assess dependency of phantom size, tissue type, and proton energy. The proton range, R ₈₀ , was extracted for each plan, and range differences were evaluated both between imaging doses and between modalities (DECT vs PCCT) at 20 mGy (inter-modality). Main results. Under reduced imaging dose, DECT showed substantial proton range differences for the large phantom sizes. It resulted in median range differences up to 20.1 mm due to visible imaging artifacts. Similar trends were seen for long proton path lengths. In contrast, for PCCT, range deviations stayed below 0.5 mm across all phantom sizes and through all tissue types. Inter-modality range variations increased when protons traversed denser tissues or longer path lengths. Significance. This work showed consistent R ₈₀ estimations for PCCT across phantom sizes and traversing different tissue types, even under reduced imaging dose in PCCT. This offers possibilities to lower the imaging dose and thus cumulative patient dose, without compromising treatment accuracy.