Background Photon-counting computed tomography (PCCT) is a promising new technology with the potential to fundamentally change today’s workflows in the daily routine and to provide new quantitative imaging information to improve clinical decision-making and patient management. Method The content of this review is based on an unrestricted literature search on PubMed and Google Scholar using the search terms “Photon-Counting CT”, “Photon-Counting detector”, “spectral CT”, “Computed Tomography” as well as on the authors’ experience. Results The fundamental difference with respect to the currently established energy-integrating CT detectors is that PCCT allows counting of every single photon at the detector level. Based on the identified literature, PCCT phantom measurements and initial clinical studies have demonstrated that the new technology allows improved spatial resolution, reduced image noise, and new possibilities for advanced quantitative image postprocessing. Conclusion For clinical practice, the potential benefits include fewer beam hardening artifacts, radiation dose reduction, and the use of new contrast agents. In this review, we will discuss basic technical principles and potential clinical benefits and demonstrate first clinical use cases. Key Points:  Citation Format

Objectives Computed tomography (CT) is employed to evaluate surgical outcome after spinal interventions. Here, we investigate the potential of multispectral photon-counting computed tomography (PC-CT) on image quality, diagnostic confidence, and radiation dose compared to an energy-integrating CT (EID-CT). Methods In this prospective study, 32 patients underwent PC-CT of the spine. Data was reconstructed in two ways: (1) standard bone kernel with 65-keV (PC-CTstd) and (2) 130-keV monoenergetic images (PC-CT130 keV). Prior EID-CT was available for 17 patients; for the remaining 15, an age–, sex–, and body mass index–matched EID-CT cohort was identified. Image quality (5-point Likert scales on overall, sharpness, artifacts, noise, diagnostic confidence) of PC-CTstd and EID-CT was assessed by four radiologists independently. If metallic implants were present (n = 10), PC-CTstd and PC-CT130 keV images were again assessed by 5-point Likert scales by the same radiologists. Hounsfield units (HU) were measured within metallic artifact and compared between PC-CTstd and PC-CT130 keV. Finally, the radiation dose (CTDIvol) was evaluated. Results Sharpness was rated significantly higher (p = 0.009) and noise significantly lower (p < 0.001) in PC-CTstd vs. EID-CT. In the subset of patients with metallic implants, reading scores for PC-CT130 keV revealed superior ratings vs. PC-CTstd for image quality, artifacts, noise, and diagnostic confidence (all p < 0.001) accompanied by a significant increase of HU values within the artifact (p < 0.001). Radiation dose was significantly lower for PC-CT vs. EID-CT (mean CTDIvol: 8.83 vs. 15.7 mGy; p < 0.001). Conclusions PC-CT of the spine with high-kiloelectronvolt reconstructions provides sharper images, higher diagnostic confidence, and lower radiation dose in patients with metallic implants. Key Points • Compared to energy-integrating CT, photon-counting CT of the spine had significantly higher sharpness and lower image noise while radiation dose was reduced by 45%. • In patients with metallic implants, virtual monochromatic photon-counting images at 130 keV were superior to standard reconstruction at 65 keV in terms of image quality, artifacts, noise, and diagnostic confidence.

Background With the clinical release of a photon counting detector-based computed tomography (CT) system, the potential benefits of this new technology need to be evaluated clinically. Literature concerning this new generation of detector is sparse, especially in the field of pediatric radiology. Therefore, this study outlines our initial experience with ultra-low dose chest CT imaging on the new photon counting CT system. Materials and methods A pediatric phantom (1-year old, CIRS ATOM phantom, model 704 [CIRS-computerized imaging reference system, Norfolk, VA]) was scanned at different dose levels and different image quality levels to define a protocol for clinical examinations. Next, 20 consecutive pediatric non-contrast ultra-low dose chest CT examinations were evaluated for radiation dose and diagnostic image quality using a 4-point Likert-scale—1 = excellent, 4 = bad image quality—by two radiologists in a consensus reading. This retrospective analysis was approved by the local research ethics committee. Results Chest CT examinations performed at ultra-low radiation dose (effective dose 0.19 ± 0.07 mSv; size-specific dose estimate 0.45 ± 0.14 mGy) in pediatric patients ages (2.6 ± 1.8 years) show good to excellent image quality for lung structures (1.4 ± 0.4) and moderate image quality for soft tissue structures (2.8 ± 0.2). Conclusion Pediatric ultra-low dose chest CT examinations are feasible with the new generation photon counting detector-based CT system. The benefits of this technology must be evaluated for pediatric patients from the outset.

Objectives: To examine if calcium scoring CT (CAS-CT) reduces the whole-examination radiation dose of prospectively ECG-triggered coronary CT-angiography (CCTA). Methods In this retrospective study, patients underwent CAS-CT and prospectively ECG-triggered CCTA on a 2nd generation Dual-Source CT scanner. CCTA was planned on CAS-CT images. We further simulated CCTA-planning on scout-view. Therefore, the scan length of the scout-view-derived CCTA was set equal to the CAS-CT scan length. Effective doses were compared for the following scenarios: (1) CAS-CT-derived CCTA + CAS-CT and (2) scout-view-derived CCTA without CAS-CT. Dose differences between the scenarios were additionally examined with respect to scan mode and body-mass-index. Results Among 182 patients (58±12 years, 47% females), planning cCTA on CAS-CT resulted in a shorter scan length than planning on scout-view (114.3 ± 9.7 mm vs 133.7 ± 13.2 mm, p<0.001). The whole-examination effective dose was slightly lower for scenario (1) (3.2 [1.8 – 5.3] mSv vs 3.4 [1.5 – 5.9] mSv; p<0.001, n=182). Scenario (1) resulted in a substantially lower radiation dose in sequential scans (3.6 [2.3 – 6.1] mSv vs 3.9 [2.4 – 6.50] mSv, n=150), or in obese patients (6.8 mSv [4.5 – 9.1]) vs 7.3 mSv [4.7 – 9.9], n=45), p<0.001 respectively. Only in high-pitch spiral CCTA, scenario (2) resulted in a dose salvage (0.8 mSv [0.6 – 1.4] vs 1.0 mSv [0.8 – 1.5], n=32; p<0.001). Conclusions Planning prospectively ECG-triggered CCTA on CAS-CT reduces the overall radiation dose of the examination compared to a scout-view planning approach where no CAS-CT is acquired. Only for high-pitch spiral CCTA a slightly opposite effect was observed.

Background: This study investigates whether the scan length adjustment of prospectively ECG-triggered coronary CT angiography (CCTA) using calcium-scoring CT (CAS-CT) images can reduce overall radiation doses. Methods: A retrospective analysis was conducted on 182 patients who underwent CAS-CT and prospectively ECG-triggered CCTA using a second-generation Dual-Source CT scanner. CCTA planning was based on CAS-CT images, for which simulated scout view planning was performed for comparison. Effective doses were compared between two scenarios: Scenario 1—CAS-CT-derived CCTA + CAS-CT and Scenario 2—scout-view-derived CCTA without CAS-CT. Dose differences were further analyzed with respect to scan mode and body mass index. Results: Planning CCTA using CAS-CT led to a shorter scan length than planning via scout view (114.3 ± 9.7 mm vs. 133.7 ± 13.2 mm, p < 0.001). The whole-examination effective dose was slightly lower for Scenario 1 (3.2 [1.8–5.3] mSv vs. 3.4 [1.5–5.9] mSv; p < 0.001, n = 182). Notably, Scenario 1 resulted in a significantly lower radiation dose for sequential scans and obese patients. Only high-pitch spiral CCTA showed dose reduction in Scenario 2. Conclusions: Using CAS-CT for planning prospectively ECG-triggered CCTA reduced the overall radiation dose administered compared to scout view planning without CAS-CT, except for high-pitch spiral CCTA, where a slightly opposite effect was observed.