Seeing More with Less: Clinical Benefits of Photon-counting Detector CT

Computed Tomography Imaging for Suspected Gastrointestinal Bleeding and Bowel Ischemia

Computed tomography (CT) is one of the main diagnostic methods for assessing both acute gastrointestinal bleeding (GIB) and bowel ischemia due to its widespread availability, excellent spatial resolution, and high accuracy. While endoscopy is the preferred diagnostic tool for workup of upper GIB, CT is used in select instances as a complementary modality or when endoscopy is impractical. For lower GIB, CT is one of the first-line imaging tools. Mesenteric ischemia is primarily diagnosed with CT, which can exquisitely assess the vasculature and demonstrate bowel findings of ischemia or infarction.

Photon-Counting Detector CT Applications in Musculoskeletal Radiology

ABSTRACT

Photon-counting detectors (PCDs) have emerged as one of the most influential technical developments for medical imaging in recent memory. Surpassing conventional systems with energy-integrating detector technology in many aspects, PCD-CT scanners provide superior spatial resolution and dose efficiency for all radiological subspecialities. Demanding detailed display of trabecular microarchitecture and extensive anatomical coverage frequently within the same scan, musculoskeletal (MSK) imaging in particular can be a beneficiary of PCD-CT's remarkable performance. Since PCD-CT provides users with a plethora of customization options for both image acquisition and reconstruction, however, MSK radiologists need to be familiar with the scanner to unlock its full potential. From filter-based spectral shaping for artifact reduction over full field-of-view ultra-high-resolution scans to postprocessing of single- or dual-source multienergy data, almost every imaging task can be met with an optimized approach in PCD-CT. The objectives of this review were to give an overview of the most promising applications of PCD-CT in MSK imaging to date, to state current limitations, and to highlight directions for future research and developments.

Delineation of the brachial plexus by contrast-enhanced photon-counting detector CT and virtual monoenergetic images

OBJECTIVES

To improve the image quality of the brachial plexus in photon-counting detector CT (PCD-CT) using contrast media and virtual monoenergetic images (VMI).

MATERIALS & METHODS

We retrospectively analyzed contrast-enhanced neck PCD-CT images scanned in March-July 2023. Unenhanced and contrast-enhanced images were compared, and then 40-, 70-, and 100-keV VMIs were compared. The qualitative evaluation used a five-point Likert scale regarding overall image quality (IQ), sharpness, and noise. The quantitative evaluation used the standard deviation (SD), signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR). Freidman's test and one-way ANOVA were performed.

RESULTS

Forty patients (65 years ± 17, 21 males) were included. The median scores [interquartile range, IQR] for the unenhanced and contrast-enhanced groups were IQ, 3 [2,3] and 4 [3,4] (P < 0.001); sharpness, 3 [2,3] and 4 [3,4] (P < 0.001); and noise, 3 [3,4] and 3 [3,4] (P = 0.63). Mean ± SD scores were SD, 6.7 ± 1.4 and 6.7 ± 1.0 (P = 0.95); SNR, 5.1 ± 1.2 and 5.4 ± 1.4 (P = 0.04); and CNR, 4.8 ± 1.5 and 8.1 ± 2.3 (P < 0.001). The 40-, 70-, and 100-keV groups' IQ were 2 [2,3], 4 [3,4], and 3 [3,4]; their sharpness scores were 2 [2,3], 3 [3,4], and 3 [2,3] (all, P < 0.05). Those for noise were 2 [1-3], 3 [3,4], and 4 [3,4] (all, P < 0.001 except for 70-keV vs.100-keV: P = 0.16). The SDs were 13.1 ± 2.5, 7.5 ± 1.2, and 6.0 ± 1.1. The SNRs were 4.2 ± 1.9, 5.0 ± 1.2, and 5.7 ± 1.5 (all, P < 0.001). The CNRs were 8.7 ± 4.0, 6.8 ± 2.3, and 6.5 ± 2.3 (all, P < 0.001 except for 70-keV vs.100-keV: P = 0.51).

CONCLUSION

Contrast-enhanced PCD-CT and VMIs provided good delineation of the brachial plexus.

Potential of photon-counting detector CT technology for contrast medium reduction in portal venous phase thoracoabdominal CT

OBJECTIVES

To compare image quality and iodine attenuation intra-individually in portal venous phase photon-counting detector CT (PCD-CT) scans using protocols with different contrast medium (CM) volume.

MATERIALS AND METHODS

A prospectively acquired patient cohort between 04/2021 and 11/2023 was retrospectively screened if patients had the following combination of portal venous phase thoracoabdominal CT scans: (a) PCD-CT with 120 mL CM volume (PCD-CT120 mL), (b) PCD-CT with 100 mL CM volume (PCD-CT100 mL), and (c) prior energy-integrating detector CT (EID-CT) with 120 mL CM volume. On PCD-CT, virtual monoenergetic image (VMI) reconstructions at 70 keV were applied for both groups as well as additional VMI at 60 keV for PCD‑CT100 mL. Quantitative analyses including signal-to-noise (SNR) and contrast-to-noise ratios (CNR) and qualitative analyses were performed using a mixed linear effects model.

RESULTS

The final study cohort comprised 49 patients (mean age 67 [31-86] years, 12 female). Comparison to EID-CT was available in 33 patients. In standard 70 keV VMI reconstructions, PCD-CT100 mL was non-inferior to PCD-CT120 mL as well as to EID-CT120 mL for CNR in abdominal organs (all p > 0.050). The mixed linear effects model revealed significant differences between contrast volume groups for both contrast enhancement and image quality ratings. PCD-CT100 mL/70 keV demonstrated the smallest deviation from optimal contrast enhancement (-0.306, p < 0.001).

CONCLUSION

In portal venous phase thoracoabdominal PCD-CT, a nearly 17% reduction in CM was achievable while maintaining subjective and objective image quality compared to prior higher CM volume PCD-CT scans within the same patients and still surpassing image quality of previous exams on an EID-CT system.

KEY POINTS

Question How do image quality and iodine attenuation intra-individually compare in portal venous phase photon-counting detector CT (PCD-CT) scans using protocols with different contrast medium volume. Findings PCD-CT scans exhibit superior quantitative and qualitative image quality compared to energy-integrating detector-CT acquisitions and are not negatively affected by contrast volume reductions up to 17%. Clinical relevance This study provides further evidence that PCD-CT enables a considerable reduction in iodine dose for portal venous phase acquisition, benefiting both patients and healthcare system costs.

Benchmarking Photon-Counting Computed Tomography Angiography Against Invasive Assessment of Coronary Stenosis: Implications for Severely Calcified Coronaries

BACKGROUND

Clinical guidelines do not recommend coronary computed tomographic angiography (CTA) in elderly patients or in the presence of heavy coronary calcification. Photon-counting coronary computed tomographic angiography (PCCTA) introduces ultrahigh in-plane resolution and multienergy imaging, but the ability of this technology to overcome these limitations is unclear.

OBJECTIVES

The authors evaluate the ability of PCCTA to quantitatively assess coronary luminal stenosis in the presence and absence of calcification, comparing both the ultrahigh-resolution (UHR)-PCCTA and the multienergy standard-resolution (SR)-PCCTA with the criterion-standard 3-dimensional invasive quantitative coronary angiography (3D QCA).

METHODS

The authors included 100 patients who had both PCCTA and invasive coronary angiography (ICA). They comparatively evaluated luminal diameter stenosis with PCCTA and 3D QCA, anatomic disease severity (according to CAD-RADS [Coronary Artery Disease-Reporting and Data System]) and the diagnostic performance of PCCTA in identifying coronary arteries with ≥50% diameter stenosis on 3D QCA requiring invasive hemodynamic severity evaluation and/or revascularization.

RESULTS

The authors analyzed 257 vessels and 343 plaques. UHR-PCCTA luminal evaluation relative to 3D QCA was more precise than SR-PCCTA (median difference: 3% [Q1-Q3: 1%-6%] vs 6% [Q1-Q3: 2%-11%]; P < 0.001), particularly in severely calcified arteries (median difference 3% [Q1-Q3: 1%-6%] vs 6% [Q1-Q3: 3%-13%]; P = 0.002). Per-vessel agreement for CAD-RADS between UHR-PCCTA and 3D QCA was near-perfect (κ = 0.90 [Q1-Q3: 0.84-0.95]; P < 0.001), and it was substantial for SR-PCCTA (κ = 0.63 [Q1-Q3: 0.54-0.71]; P < 0.001), especially in severely calcified arteries: κ = 0.90 (Q1-Q3: 0.83-0.97; P < 0.001) and κ = 0.67 (Q1-Q3: 0.56-0.77; P < 0.001), respectively. Per-vessel diagnostic performance of SR- and UHR-PCCTA was excellent: AUC: 0.94 (95% CI: 0.91-0.98; P < 0.001) and 0.99 (95% CI: 0.98-1.00; P < 0.001), respectively. UHR-PCCTA diagnostically outperformed SR-PCCTA: ΔAUC: 0.05 (95% CI: 0.01-0.08; P = 0.01).

CONCLUSIONS

PCCTA compares favorably with ICA for lumen assessment and anatomic disease severity classification in patients presenting with acute coronary syndrome or patients referred for ICA. UHR-PCCTA luminal evaluation is superior to SR-PCCTA, especially in patients with heavy coronary calcification. UHR-PCCTA has excellent diagnostic performance in identifying coronary arteries with ≥50% luminal stenosis on 3D QCA, outperforming standard-resolution imaging.

Performance of iodine quantification through high-pitch dual-source photon-counting CT: a phantom study

PURPOSE

To investigate the feasibility and accuracy of iodine quantification using PCD-CT in standard-pitch and high-pitch scanning at different scan parameters in a phantom model.

MATERIALS AND METHODS

Four inserts with known iodine concentrations (2, 5, 10, and 15 mg/mL) were placed in the removable CT phantom and scanned using high-pitch (3.2) and standard-pitch (0.8) modes on PCD-CT. Two tube voltages (120 and 140 kVp) and four radiation doses (1, 3, 5, and 10 mGy) were alternated. Each scan setting was repeated three times. Mean iodine concentration for each insert across three consecutive slices was recorded. Percentage absolute bias (PAB) was assessed for iodine quantification.

RESULTS

A total of 96 acquisitions were conducted. In small phantom, the average for PAB was 2.96% (range: 1.75% ~ 4.56%) and 1.67% (range: 1.00% ~ 3.42%) for high-pitch and standard-pitch acquisitions, respectively. In large phantom, it was 3.72% (range: 1.75% ~ 5.97%) and 2.94% (range: 1.75% ~ 4.70%). Linear regression analysis revealed that only phantom size significantly influenced (P < 0.001) the accuracy of iodine quantification.

CONCLUSION

The high-pitch scan mode in PCD-CT can be used to quantify iodine density with similar accuracy compared with standard pitch.

Improved display and detection of small renal stones using photon-counting detector CT compared to conventional energy-integrating detector CT

PURPOSE

To compare same-day photon-counting detector CT (PCD-CT) to conventional energy-integrating detector CT (EID-CT) for detection of small renal stones (≤ 3 mm).

METHODS

Patients undergoing clinical dual-energy EID-CT for known or suspected stone disease underwent same-day research PCD-CT. Patients with greater than 10 stones and no visible stones under 3 mm were excluded. Three radiologists selected the optimal reconstruction configuration for each CT modality and created the reference standard for renal stone presence. Two other radiologists, blinded to imaging modality, independently reviewed anonymized images to detect renal stones, rating confidence in potential stones using a Likert scale (1 = Definitely present, 2 = Probably present, 3 = Questionably present, 4 = Not seen). Sensitivity and false positive detections for PCD and EID-CT were calculated.

RESULTS

Twenty-one patients underwent clinical EID-CT followed by same-day PCD-CT, with the reference standard identifying 121 renal stones (mean size 2.8 ± 2.6 mm). 0.4-mm PCD-CT images were more likely to display a stone as definitely present compared to 1- or 2-mm EID-CT images (p < 0.0001). Overall sensitivity for detection of all stones was greater at PCD-CT (0.75 vs. 0.55, p < 0.05). Pooled sensitivity of stones ≤ 3 mm was also significantly higher at PCD-CT (0.67 vs. 0.41, p < 0.05), with false positive detections differing between readers and modalities (PCD-CT vs. EID-CT: R1-7 v. 5; R2 - 7 v. 1).

CONCLUSION

Sensitivity for renal stones was significantly higher using high spatial resolution PCD-CT vs. EID-CT, especially for stones 3 mm or less in size, which may be important for at-risk patient populations. Prospective evaluation in larger patient populations that will benefit from detection of small stones is warranted.

Clinical and imaging aspects of pulmonary embolism: a primer for radiologists

Although many advancements have been made in imaging modalities that can be used to diagnose pulmonary embolism (PE), computed tomography pulmonary angiography (CTPA) is still the preferred gold standard for promptly diagnosing pulmonary embolism by looking for filling defects caused by the embolus lodged within the main pulmonary artery or its respective branches. The diagnosis is made by the radiologists in emergency settings where quick detection of a PE on CTPA helps the Pulmonary Embolism Response Team (PERT) in quick management. Thus, utmost care is needed to follow standard image acquisition protocols and optimal contrast administration techniques to achieve a contrast opacification of at least 210 Hounsfield units for the radiologists to easily pinpoint an embolus within the pulmonary arteries. Even following proper CTPA scan acquisition guidelines, a CTPA image is prone to several artifacts that can be mistaken for a PE, resulting in a false positive read. In addition to this, many incidental findings, that can be the etiology of chest pain in a PE-suspected patient, are often overlooked by emergency radiologists who try to be as quick as possible in their read so that timely management of PE can be ensued. Taking this into account, our review paper provides the audience with a comprehensive understanding of the clinical aspects of pulmonary embolism and the imaging modalities used for PE detection. The main focus is on CTPA, its acquisition protocols, and the various incidental findings and artifacts to look for while interpreting a CTPA scan. PRéCIS: Beyond the filling defects, a CTPA scan should also be assessed by the radiologists for any incidental findings while keeping in mind several associated pitfalls and artifacts of CTPA.

Photon-counting detector CT - first experiences in the field of musculoskeletal radiology

The introduction of photon-counting detector CT (PCD-CT) marks a remarkable leap in innovation in CT imaging. The new detector technology allows X-rays to be converted directly into an electrical signal without an intermediate step via a scintillation layer and allows the energy of individual photons to be measured. Initial data show high spatial resolution, complete elimination of electronic noise, and steady availability of spectral image data sets. In particular, the new technology shows promise with respect to the imaging of osseous structures. Recently, PCD-CT was implemented in the clinical routine. The aim of this review was to summarize recent studies and to show our first experiences with photon-counting detector technology in the field of musculoskeletal radiology.We performed a literature search using Medline and included a total of 90 articles and reviews that covered recent experimental and clinical experiences with the new technology.In this review, we focus on (1) spatial resolution and delineation of fine anatomic structures, (2) reduction of radiation dose, (3) electronic noise, (4) techniques for metal artifact reduction, and (5) possibilities of spectral imaging. This article provides insight into our first experiences with photon-counting detector technology and shows results and images from experimental and clinical studies. · This review summarizes recent experimental and clinical studies in the field of photon-counting detector CT and musculoskeletal radiology.. · The potential of photon-counting detector technology in the field of musculoskeletal radiology includes improved spatial resolution, reduction in radiation dose, metal artifact reduction, and spectral imaging.. · PCD-CT enables imaging at lower radiation doses while maintaining or even enhancing spatial resolution, crucial for reducing patient exposure, especially in repeated or prolonged imaging scenarios.. · It offers promising results in reducing metal artifacts commonly encountered in orthopedic or dental implants, enhancing the interpretability of adjacent structures in postoperative and follow-up imaging.. · With its ability to routinely acquire spectral data, PCD-CT scans allow for material classification, such as detecting urate crystals in suspected gout or visualizing bone marrow edema, potentially reducing reliance on MRI in certain cases.. Bette S, Risch F, Becker J et al. Photon-counting detector CT - first experiences in the field of musculoskeletal radiology. Fortschr Röntgenstr 2024; DOI 10.1055/a-2312-6914.

Quantitative multi-energy CT in oncology: State of the art and future directions

Multi-energy computed tomography (CT) involves acquisition of two or more CT measurements with distinct energy spectra. Using the differential attenuation of tissues and materials at different X-ray energies, multi-energy CT allows distinction of tissues and materials. Multi-energy technology encompasses different types of CT systems, such as dual-energy CT and photon-counting CT, that can use information from the energy and type of material present in acquired images to create multiple datasets. These scanners have overcome many of the limitations of conventional CT, making it possible to improve the diagnostic performance of CT and expand its use to new applications through better tissue characterization and multiple quantitative parameters. Quantitative imaging biomarkers based on multi-energy CT have enormous potential in oncologic imaging, from the diagnosis and characterization of tumor phenotypes to the evaluation of the response to treatment. Nevertheless, implementing these techniques in clinical practice remains challenging. This article reviews the basic principles underlying multi-energy CT and the most recent technical developments in these systems together with their advantages and limitations to establish the value of quantitative imaging derived from multi-energy CT in the field of oncology.

Improved Pulmonary Artery Evaluation Using High-Pitch Photon-Counting CT Compared to High-Pitch Conventional or Routine-Pitch Conventional Dual-Energy CT

OBJECTIVE

Pulmonary CT angiography (CTA) to detect pulmonary emboli can be performed using conventional dual-source CT with single-energy acquisition at high-pitch (high-pitch conventional CT), which minimizes motion artifacts, or routine-pitch, dual-energy acquisitions (routine-pitch conventional DECT), which maximize iodine signal. We compared iodine signal, radiation dose, and motion artifacts of pulmonary CTA between these conventional CT modalities and dual-source photon-counting detector CT with high-pitch, multienergy acquisitions (high-pitch photon-counting CT).

METHODS

Consecutive clinically indicated pulmonary CTA exams were collected. CT number/noise was measured from the main to right lower lobe segmental pulmonary arteries using 120 kV threshold low, 120 kV, and mixed kV (0.6 linear blend) images. Three radiologists reviewed anonymized, randomized exams, rating them using a 4- or 5-point Likert scale (1 = worst, and 4/5 = best) for contrast enhancement in pulmonary arteries, motion artifacts in aortic root to subsegmental pulmonary arteries, lung image quality; pulmonary blood volume (PBV) map image quality (for multienergy or dual-energy exams), and contribution to reader confidence.

RESULTS

One hundred fifty patients underwent high-pitch photon-counting CT (n = 50), high-pitch conventional CT (n = 50), and routine-pitch conventional DECT (n = 50). High-pitch photon-counting CT had lower radiation dose (CTDI vol : 8.1 ± 2.5 vs 9.6 ± 6.8 and 16.2 ± 8.5 mGy, respectively; P < 0.001), and routine-pitch conventional DECT had significantly less contrast ( P < 0.009). CT number and CNR measurements were significantly greater at high-pitch photon-counting CT ( P < 0.001). Across readers, high-pitch photon-counting CT demonstrated significantly higher subjective contrast enhancement in the pulmonary arteries compared to the other modalities (4.7 ± 0.6 vs 4.4 ± 0.7 vs 4.3 ± 0.7; P = 0.011) and lung image quality (3.4 ± 0.5 vs 3.1 ± 0.5 vs 3.1 ± 0.5; P = 0.013). High-pitch photon-counting CT and high-pitch conventional CT had fewer motion artifacts at all levels compared to DECT ( P < 0.001). High-pitch photon-counting CT PBV maps had superior image quality ( P < 0.001) and contribution to reader confidence ( P < 0.001) compared to routine-pitch conventional DECT.

CONCLUSION

High-pitch photon-counting pulmonary CTA demonstrated higher contrast in pulmonary arteries at lower radiation doses with improved lung image quality and fewer motion artifacts compared to high-pitch conventional CT and routine-pitch conventional dual-energy CT.

Diagnostic Methods of Atherosclerotic Plaque and the Assessment of Its Prognostic Significance-A Narrative Review

Cardiovascular diseases (CVD) are a leading cause of death. The most notable cause of CVD is an atherosclerotic plaque. The aim of this review is to provide an overview of different diagnostic methods for atherosclerotic plaque relevant to the assessment of cardiovascular risk. The methods can be divided into invasive and non-invasive. This review focuses on non-invasive with attention paid to ultrasonography, contrast-enhanced ultrasonography, intravascular ultrasonography, and assessment of intima-media complex, coronary computed tomography angiography, and magnetic resonance. In the review, we discuss a number of Artificial Intelligence technologies that support plaque imaging.

Ultra-high-resolution photon-counting detector CT for visualization of the brachial plexus

OBJECTIVES

To investigate the use of photon-counting detector CT (PCD-CT) to improve brachial plexus depiction.

MATERIALS AND METHODS

This retrospective study included patients who underwent neck CT from March to December 2023. To assess the optimal reconstruction condition in PCD-CT, the signal-to-noise ratios (SNRs) on images using various quantitative regular (Qr) kernels and strengths of quantum iterative reconstruction (QIR) were evaluated. Next, images obtained by ultra-high-resolution mode in PCD-CT (PCD-UHR), standard mode in PCD-CT (PCD-STD), and standard mode in energy-integrating detector CT (EID-STD) of 20 patients each were compared regarding brachial plexus depiction. A qualitative evaluation was performed using a 5-point Likert scale regarding sharpness, noise, and overall image quality. The standard deviations (SDs), SNRs, and contrast-to noise ratios (CNRs) were quantitatively evaluated.

RESULTS

Overall, 60 patients (mean age, 63 years ± 18; 30 males) were included. The SNRs for the Qr40 and QIR4 (means ± SDs) were 3.6 ± 1.1 and 4.1 ± 1.2, respectively, significantly higher than others (P < 0.05). The scores for overall image quality were 4 [4-5], 3 [3-4], and 2 [2-3], and those for sharpness were 4 [3-5], 3 [3-3], and 2 [1-3] for PCD-UHR, PCD-STD, and EID-STD, respectively (all, P < 0.05). Those for noise were 3 [3-4], 4 [3-4], and 2 [2-2], the SDs were 6.6 ± 1.6, 5.4 ± 0.8, and 8.8 ± 1.7, SNRs were 5.0 ± 1.4, 6,1 ± 1.2, and 3.5 ± 1.6, and CNRs were 5.6 ± 1.9, 7.9 ± 1.7, and 4.4 ± 1.8, respectively (between either of the PCD groups and EID-STD, P < 0.05).

CONCLUSION

PCD-CT showed superior delineation for brachial plexus to EID-CT.

High-Resolution Head CTA: A Prospective Patient Study Comparing Image Quality of Photon-Counting Detector CT and Energy-Integrating Detector CT

BACKGROUND AND PURPOSE

Photon-counting detector CT (PCD-CT) is now clinically available and offers ultra-high-resolution (UHR) imaging. Our purpose was to prospectively evaluate the relative image quality and impact on diagnostic confidence of head CTA images acquired by using a PCD-CT compared with an energy-integrating detector CT (EID-CT).

MATERIALS AND METHODS

Adult patients undergoing head CTA on EID-CT also underwent a PCD-CT research examination. For both CT examinations, images were reconstructed at 0.6 mm by using a matched standard resolution (SR) kernel. Additionally, PCD-CT images were reconstructed at the thinnest section thickness of 0.2 mm (UHR) with the sharpest kernel, and denoised with a deep convolutional neural network (CNN) algorithm (PCD-UHR-CNN). Two readers (R1, R2) independently evaluated image quality in randomized, blinded fashion in 2 sessions, PCD-SR versus EID-SR and PCD-UHR-CNN versus EID-SR. The readers rated overall image quality (1 [worst] to 5 [best]) and provided a Likert comparison score (-2 [significantly inferior] to 2 [significantly superior]) for the 2 series when compared side-by-side for several image quality features, including visualization of specific arterial segments. Diagnostic confidence (0-100) was rated for PCD versus EID for specific arterial findings, if present.

RESULTS

Twenty-eight adult patients were enrolled. The volume CT dose index was similar (EID: 37.1 ± 4.7 mGy; PCD: 36.1 ± 4.0 mGy). Overall image quality for PCD-SR and PCD-UHR-CNN was higher than EID-SR (eg, PCD-UHR-CNN versus EID-SR: 4.0 ± 0.0 versus 3.0 ± 0.0 (R1), 4.9 ± 0.3 versus 3.0 ± 0.0 (R2); all P values < .001). For depiction of arterial segments, PCD-SR was preferred over EID-SR (R1: 1.0-1.3; R2: 1.0-1.8), and PCD-UHR-CNN over EID-SR (R1: 0.9-1.4; R2: 1.9-2.0). Diagnostic confidence of arterial findings for PCD-SR and PCD-UHR-CNN was significantly higher than EID-SR: eg, PCD-UHR-CNN versus EID-SR: 93.0 ± 5.8 versus 78.2 ± 9.3 (R1), 88.6 ± 5.9 versus 70.4 ± 5.0 (R2); all P values < .001.

CONCLUSIONS

PCD-CT provides improved image quality for head CTA images compared with EID-CT, both when PCD and EID reconstructions are matched, and to an even greater extent when PCD-UHR reconstruction is combined with a CNN denoising algorithm.

Approaches, advantages, and challenges to photon counting detector and multi-energy CT

Photon counting detector CT (PCD-CT) is the newest major development in CT technology and has been commercially available since 2021. It offers major technological advantages over current standard-of-care energy integrating detector CT (EID-CT) including improved spatial resolution, improved iodine contrast to noise ratio, multi-energy imaging, and reduced noise. This article serves as a foundational basis to the technical approaches and concepts of PCD-CT technology with primary emphasis on detector technology in direct comparison to EID-CT. The article also addresses current technological challenges to PCD-CT with particular attention to cross talk and its causes (e.g., Compton scattering, fluorescence, charge sharing, K-escape) as well as pile-up.

Standardizing technical parameters and terms for abdominopelvic photon-counting CT: laying the groundwork for innovation and evidence sharing

Photon-counting detector CT (PCD-CT) is a new technology that has multiple diagnostic benefits including increased spatial resolution, iodine signal, and radiation dose efficiency, as well as multi-energy imaging capability, but which also has unique challenges in abdominal imaging. The purpose of this work is to summarize key features, technical parameters, and terms, which are common amongst current abdominopelvic PCD-CT systems and to propose standardized terminology (where none exists). In addition, user-selectable protocol parameters are highlighted to facilitate both scientific evaluation and early clinical adoption. Unique features of PCD-CT systems include photon-counting detectors themselves, energy thresholds and bins, and tube potential considerations for preserved spectral separation. Key parameters for describing different PCD-CT systems are reviewed and explained. While PCD-CT can generate multi-energy images like dual-energy CT, there are new types of images such as threshold images, energy bin images, and special spectral images. The standardized terms and concepts herein build upon prior interdisciplinary consensus and have been endorsed by the newly created Society of Abdominal Radiology Photon-counting CT Emerging Technology Commission.

Photon-Counting CT in the Head and Neck: Current Applications and Future Prospects

Photon-counting detectors (PCDs) represent a major milestone in the evolution of CT imaging. CT scanners using PCD systems have already been shown to generate images with substantially greater spatial resolution, superior iodine contrast-to-noise ratio, and reduced artifact compared with conventional energy-integrating detector-based systems. These benefits can be achieved with considerably decreased radiation dose. Recent studies have focused on the advantages of PCD-CT scanners in numerous anatomic regions, particularly the coronary and cerebral vasculature, pulmonary structures, and musculoskeletal imaging. However, PCD-CT imaging is also anticipated to be a major advantage for head and neck imaging. In this paper, we review current clinical applications of PCD-CT in head and neck imaging, with a focus on the temporal bone, facial bones, and paranasal sinuses; minor arterial vasculature; and the spectral capabilities of PCD systems.

Multisystem Imaging Manifestations of Kidney Failure

Kidney failure (KF) refers to a progressive decline in glomerular filtration rate to below 15 ml/min per 1.73 m2, necessitating renal replacement therapy with dialysis or renal transplant. The hemodynamic and metabolic alterations in KF combined with a proinflammatory and coagulopathic state leads to complex multisystemic complications. The imaging hallmark of systemic manifestations of KF is bone resorption caused by secondary hyperparathyroidism. Other musculoskeletal complications include brown tumor, osteosclerosis, calcinosis, soft-tissue calcification, and amyloid arthropathy. Cardiovascular complications and infections are the leading causes of death in KF. Cardiovascular complications include accelerated atherosclerosis, cardiomyopathy, pericarditis, myocardial calcinosis, and venous thromboembolism. Neurologic complications such as encephalopathy, osmotic demyelination, cerebrovascular disease, and opportunistic infections are also frequently encountered. Pulmonary complications include edema and calcifications. Radiography and CT are used in assessing musculoskeletal and thoracic complications, while MRI plays a key role in assessing neurologic and cardiovascular complications. CT iodinated contrast material is generally avoided in patients with KF except in situations where the benefit of contrast-enhanced CT outweighs the risks and in patients already undergoing maintenance dialysis. At MRI, group II gadolinium-based contrast material can be safely administered in patients with KF. The authors discuss the extrarenal systemic manifestations of KF, the choice of imaging modality in their assessment, and imaging findings of complications. ©RSNA, 2024 Supplemental material is available for this article.

Submillisievert Abdominal Photon-Counting CT versus Energy-integrating Detector CT for Urinary Calculi Detection: Impact on Diagnostic Confidence

Background Contrast-unenhanced abdominal CT is the imaging standard for urinary calculi detection; however, studies comparing photon-counting detector (PCD) CT and energy-integrating detector (EID) CT dose-reduction potentials are lacking. Purpose To compare the radiation dose and image quality of optimized EID CT with those of an experimental PCD CT scan protocol including tin prefiltration in patients suspected of having urinary calculi. Materials and Methods This retrospective single-center study included patients who underwent unenhanced abdominal PCD CT or EID CT for suspected urinary caliculi between February 2022 and March 2023. Signal and noise measurements were performed at three anatomic levels (kidney, psoas, and obturator muscle). Nephrolithiasis and/or urolithiasis presence was independently assessed by three radiologists, and diagnostic confidence was recorded on a five-point scale (1, little to no confidence; 5, complete confidence). Reader agreement was determined by calculating Krippendorff α. Results A total of 507 patients (mean age, 51.7 years ± 17.4 [SD]; 317 male patients) were included (PCD CT group, 229 patients; EID CT group, 278 patients). Readers 1, 2, and 3 detected nephrolithiasis in 129, 127, and 129 patients and 94, 94, and 94 patients, whereas the readers detected urolithiasis in 113, 114, and 114 patients and 152, 153, and 152 patients in the PCD CT and EID CT groups, respectively. Regardless of protocol (PCD CT or EID CT) or calculus localization, near perfect interreader agreement was found (α ≥ 0.99; 95% CI: 0.99, 1). There was no evidence of a difference in reader confidence between PCD CT and EID CT (median confidence, 5; IQR, 5-5; P ≥ .57). The effective doses were 0.79 mSv (IQR, 0.63-0.99 mSv) and 1.39 mSv (IQR, 1.01-1.87 mSv) for PCD CT and EID CT, respectively. Despite the lower radiation exposure, the signal-to-noise ratios at the kidney, psoas, and obturator levels were 30%, 23%, and 17% higher, respectively, in the PCD CT group (P < .001). Conclusion Submillisievert abdominal PCD CT provided high-quality images for the diagnosis of urinary calculi; radiation exposure was reduced by 44% with a higher signal-to-noise ratio than with EID CT and with no evidence of a difference in reader confidence. Published under a CC BY 4.0 license. Supplemental material is available for this article. See also the editorial by Nezami and Malayeri in this issue.

Back to the Future: Dynamic Contrast-Enhanced Photon-Counting Detector CT for the Detection of Pituitary Adenoma in Cushing Disease

Historically, MR imaging has been unable to detect a pituitary adenoma in up to one-half of patients with Cushing disease. This issue is problematic because the standard-of-care treatment is surgical resection, and its success is correlated with finding the tumor on imaging. Photon-counting detector CT is a recent advancement that has multiple benefits over conventional energy-integrating detector CT. We present the use of dynamic contrast-enhanced imaging using photon-counting detector CT for the detection of pituitary adenomas in patients with Cushing disease.

Photon-counting CT in Thoracic Imaging: Early Clinical Evidence and Incorporation Into Clinical Practice

Photon-counting CT (PCCT) is an emerging advanced CT technology that differs from conventional CT in its ability to directly convert incident x-ray photon energies into electrical signals. The detector design also permits substantial improvements in spatial resolution and radiation dose efficiency and allows for concurrent high-pitch and high-temporal-resolution multienergy imaging. This review summarizes (a) key differences in PCCT image acquisition and image reconstruction compared with conventional CT; (b) early evidence for the clinical benefit of PCCT for high-spatial-resolution diagnostic tasks in thoracic imaging, such as assessment of airway and parenchymal diseases, as well as benefits of high-pitch and multienergy scanning; (c) anticipated radiation dose reduction, depending on the diagnostic task, and increased utility for routine low-dose thoracic CT imaging; (d) adaptations for thoracic imaging in children; (e) potential for further quantitation of thoracic diseases; and (f) limitations and trade-offs. Moreover, important points for conducting and interpreting clinical studies examining the benefit of PCCT relative to conventional CT and integration of PCCT systems into multivendor, multispecialty radiology practices are discussed.

Material decomposition with a prototype photon-counting detector CT system: expanding a stoichiometric dual-energy CT method via energy bin optimization and K-edge imaging

Objective.Computed tomography (CT) has advanced since its inception, with breakthroughs such as dual-energy CT (DECT), which extracts additional information by acquiring two sets of data at different energies. As high-flux photon-counting detectors (PCDs) become available, PCD-CT is also becoming a reality. PCD-CT can acquire multi-energy data sets in a single scan by spectrally binning the incident x-ray beam. With this, K-edge imaging becomes possible, allowing high atomic number (high-Z) contrast materials to be distinguished and quantified. In this study, we demonstrated that DECT methods can be converted to PCD-CT systems by extending the method of Bourqueet al(2014). We optimized the energy bins of the PCD for this purpose and expanded the capabilities by employing K-edge subtraction imaging to separate a high-atomic number contrast material.Approach.The method decomposes materials into their effective atomic number (Zeff) and electron density relative to water (ρe). The model was calibrated and evaluated using tissue-equivalent materials from the RMI Gammex electron density phantom with knownρevalues and elemental compositions. TheoreticalZeffvalues were found for the appropriate energy ranges using the elemental composition of the materials.Zeffvaried slightly with energy but was considered a systematic error. Anex vivobovine tissue sample was decomposed to evaluate the model further and was injected with gold chloride to demonstrate the separation of a K-edge contrast agent.Main results.The mean root mean squared percent errors on the extractedZeffandρefor PCD-CT were 0.76% and 0.72%, respectively and 1.77% and 1.98% for DECT. The tissue types in theex vivobovine tissue sample were also correctly identified after decomposition. Additionally, gold chloride was separated from theex vivotissue sample with K-edge imaging.Significance.PCD-CT offers the ability to employ DECT material decomposition methods, along with providing additional capabilities such as K-edge imaging.

Staging of breast cancer in the breast and regional lymph nodes using contrast-enhanced photon-counting detector CT: accuracy and potential impact on patient management

OBJECTIVES

To describe the feasibility and evaluate the performance of multiphasic photon-counting detector (PCD) CT for detecting breast cancer and nodal metastases with correlative dynamic breast MRI and digital mammography as the reference standard.

METHODS

Adult females with biopsy-proven breast cancer undergoing staging breast MRI were prospectively recruited to undergo a multiphasic PCD-CT using a 3-phase protocol: a non-contrast ultra-high-resolution (UHR) scan and 2 intravenous contrast-enhanced scans with 50 and 180 s delay. Three breast radiologists compared CT characteristics of the index malignancy, regional lymphadenopathy, and extramammary findings to MRI.

RESULTS

Thirteen patients underwent both an MRI and PCD-CT (mean age: 53 years, range: 36-75 years). Eleven of thirteen cases demonstrated suspicious mass or non-mass enhancement on PCD-CT when compared to MRI. All cases with metastatic lymphadenopathy (3/3 cases) demonstrated early avid enhancement similar to the index malignancy. All cases with multifocal or multicentric disease on MRI were also identified on PCD-CT (3/3 cases), including a 4 mm suspicious satellite lesion. Four of five patients with residual suspicious post-biopsy calcifications on mammograms were detected on the UHR PCD-CT scan. Owing to increased field-of-view at PCD-CT, a 5 mm thoracic vertebral metastasis was identified at PCD-CT and not with the breast MRI.

CONCLUSIONS

A 3-phase PCD-CT scan protocol shows initial promising results in characterizing breast cancer and regional lymphadenopathy similar to MRI and detects microcalcifications in 80% of cases.

ADVANCES IN KNOWLEDGE

UHR and spectral capabilities of PCD-CT may allow for comprehensive characterization of breast cancer and may represent an alternative to breast MRI in select cases.

Unlocking the potential of photon counting detector CT for paediatric imaging: a pictorial essay

Recent advancements in CT technology have introduced a revolutionary innovation to practice known as the Photon-Counting detector (PCD) CT imaging. The pivotal hardware enhancement of the PCD-CT scanner lies in its detectors, which consist of smaller pixels than standard detectors and allow direct conversion of individual X-rays to electrical signals. As a result, CT images are reconstructed at higher spatial resolution (as low as 0.2 mm) and reduced overall noise, at no expense of an increased radiation dose. These features are crucial for paediatric imaging, especially for infants and young children, where anatomical structures are notably smaller than in adults and in whom keeping dose as low as possible is especially relevant. Since January 2022, our hospital has had the opportunity to work with PCD-CT technology for paediatric imaging. This pictorial review will showcase clinical examples of PCD-CT imaging in children. The aim of this pictorial review is to outline the potential paediatric applications of PCD-CT across different anatomical regions, as well as to discuss the benefits in utilizing PCD-CT in comparison to conventional standard energy integrating detector CT.

Myocardial late enhancement and extracellular volume with single-energy, dual-energy, and photon-counting computed tomography

Computed tomography late enhancement (CT-LE) is emerging as a non-invasive technique for cardiac diagnosis with wider accessibility compared to MRI, despite its typically lower contrast-to-noise ratio. Optimizing CT-LE image quality necessitates a thorough methodology addressing contrast administration, timing, and radiation dose, alongside a robust understanding of extracellular volume (ECV) quantification methods. This review summarizes CT-LE protocols, clinical utility, and advances in ECV measurement through both single-energy and dual-energy CT. It also highlights photon-counting detector CT technology as an innovative means to potentially improve image quality and reduce radiation exposure.

Potential benefits of photon counting detector computed tomography in pediatric imaging

Photon counting detector (PCD) CT represents the newest advance in CT technology, with improved radiation dose efficiency, increased spatial resolution, inherent spectral imaging capabilities, and the ability to eliminate electronic noise. Its design fundamentally differs from conventional energy integrating detector CT because photons are directly converted to electrical signal in a single step. Rather than converting X-rays to visible light and having an output signal that is a summation of energies, PCD directly counts each photon and records its individual energy information. The current commercially available PCD-CT utilizes a dual-source CT geometry, which allows 66 ms cardiac temporal resolution and high-pitch (up to 3.2) scanning. This can greatly benefit pediatric patients by facilitating high quality fast scanning to allow sedation-free imaging. The energy-resolving nature of the utilized PCDs allows "always-on" dual-energy imaging capabilities, such as the creation of virtual monoenergetic, virtual non-contrast, virtual non-calcium, and other material-specific images. These features may be combined with high-resolution imaging, made possible by the decreased size of individual detector elements and the absence of interelement septa. This work reviews the foundational concepts associated with PCD-CT and presents examples to highlight the benefits of PCD-CT in the pediatric population.

Ultra-high-resolution photon-counting detector computed tomography of the lungs: Phantom and clinical assessment of radiation dose and image quality

PURPOSE

Photon-counting-detector computed tomography (PCD-CT) offers enhanced noise reduction, spatial resolution, and image quality in comparison to energy-integrated-detectors CT (EID-CT). These hypothesized improvements were compared using PCD-CT ultra-high (UHR) and standard-resolution (SR) scan-modes.

METHODS

Phantom scans were obtained with both EID-CT and PCD-CT (UHR, SR) on an adult body-phantom. Radiation dose was measured and noise levels were compared at a minimum achievable slice thickness of 0.5 mm for EID-CT, 0.2 mm for PCD-CT-UHR and 0.4 mm for PCD-CT-SR. Signal-to-noise ratios (SNR) and contrast-to-noise ratios (CNR) were calculated for five tissue densities. Additionally, data from 25 patients who had PCD-CT of chest were reconstructed at 1 mm and 0.2 mm (UHR) slice-thickness and compared quantitatively (SNR) and qualitatively (noise, quality, sharpness, bone details).

RESULTS

Phantom PCD-CT-UHR and PCD-CT-SR scans had similar measured radiation dose (16.0mGy vs 15.8 mGy). Phantom PCD-CT-SR (0.4 mm) had lower noise level in comparison to EID-CT (0.5 mm) (9.0HU vs 9.6HU). PCD-CT-UHR (0.2 mm) had slightly higher noise level (11.1HU). Phantom PCD-CT-SR (0.4 mm) had higher SNR in comparison to EID-CT (0.5 mm) while achieving higher resolution (Bone 115 vs 96, Acrylic 14 vs 14, Polyethylene 11 vs 10). SNR was slightly lower across all densities for PCD-CT UHR (0.2 mm). Interestingly, CNR was highest in the 0.2 mm PCD-CT group; PCD-CT CNR was 2.45 and 2.88 times the CNR for 0.5 mm EID-CT for acrylic and poly densities. Clinical comparison of SNR showed predictably higher SNR for 1 mm (30.3 ± 10.7 vs 14.2 ± 7, p = 0.02). Median subjective ratings were higher for 0.2 mm UHR vs 1 mm PCD-CT for nodule contour (4.6 ± 0.3 vs 3.6 ± 0.1, p = 0.02), bone detail (5 ± 0 vs 4 ± 0.1, p = 0.001), image quality (5 ± 0.1 vs 4.6 ± 0.4, p = 0.001), and sharpness (5 ± 0.1 vs 4 ± 0.2).

CONCLUSION

Both UHR and SR PCD-CT result in similar radiation dose levels. PCD-CT can achieve higher resolution with lower noise level in comparison to EID-CT.

Photon Counting Computed Tomography-Applications

Photon-counting detector CT (PCCT) is a new technology that has recently emerged as a powerful tool for a more precise, patient-centered imaging. Ever since the FDA approved the first Photon-counting system on September 30, 2021, this new technology raised much interest all over the scientific community and numerous studies have been published in a short period of time. By the end of 2022, the first results of phantom and in-vivo studies started showing the great potential of this new imaging modality, with benefits that range from neuroradiology to abdominal imaging and the promise to push previous limits of both patient size and age as well as image resolution. In this article, we will provide a brief explanation of how commercially available photon-counting detector CTs work and how they differ from energy-integrating detector CT systems. Then we will focus on the different clinical applications of this new technology with an in-depth systematic approach based on the most recent evidence. Because nearly every subspecialty of radiology has had impressive results, we will delve into each of these subspecialties and explain how every single domain can undergo significant transformation. This includes a wide range of possibilities, from the opportunistic screening of many different pathologies to the ability of seeing small structures with unprecedented precision, as well as a new kind of multi-energy imaging that can provide much more information on tissue characteristics, all while maintaining a lighter workflow and post-processing burden compared to what has been observed in the past.