Photon-counting detector CT for abdominal imaging: opportunities and challenges

Lesion Visualization of an Oral Manganese Contrast Agent Compared to Unenhanced MRI and Gadobenate Dimeglumine in Patients Undergoing Liver Magnetic Resonance Imaging for Evaluation of Colorectal Cancer Metastases: Centralized Assessment of a Randomized, Crossover, Phase II Study

OBJECTIVES

The primary objective of this study was to evaluate the visualization capability of orally administered manganese chloride tetrahydrate (ACE-MBCA [Ascelia Pharma-manganese-based contrast agent, also referred to as Orviglance or CMC-001]), a novel liver-specific contrast agent developed by Ascelia Pharma, as a liver-specific MRI contrast agent compared with that of the unenhanced MRI for focal liver lesions in a properly blinded study design. The secondary objective was to compare the performance of ACE-MBCA with gadobenate dimeglumine.

MATERIALS AND METHODS

Three independent readers analyzed MRI examinations from a previously completed randomized crossover clinical trial in a blinded manner in a centralized setting. The study included 20 consecutive adult patients with known or suspected liver metastases, who received both ACE-MBCA and gadobenate dimeglumine. The readers evaluated 6 types of MRI scans (unenhanced, enhanced, and combined MRI for both contrast agents) with lesion visualization [lesion border delineation (LBD) and lesion contrast (LC)] as primary outcome. To maintain the blinded nature of the study, all statistical analyses were performed by an independent statistician who was not involved in the image reading process. Differences in primary outcomes were performed using 1-sided paired t tests at a significance level of 0.025 for both parameters. For secondary outcomes (ACE-MBCA enhanced MRI visualization, lesion detection, size measurements, reader confidence, quantitative parameters, and image quality were compared with that of the other scans), descriptive statistics and 95% confidence intervals were used to evaluate differences between categories in comparative analyses, without formal hypothesis testing for most secondary endpoints.

RESULTS

ACE-MBCA-enhanced MRI demonstrated statistically significant superior scoring over unenhanced MRI for visualizing focal liver lesions, with mean LBD scores improving from 1.8-2.3 to 2.4-2.9 and LC scores ranging from 1.8-2.3 to 2.8-3.3 across all 3 readers (P < 0.001). Compared with unenhanced MRI, ACE-MBCA detected significantly more lesions across all readers (mean differences 0.4-0.8 lesions, 95% CI: 0.04-1.52), particularly for small lesions (<1 cm), where detection improved from 2-6 to 3-12 lesions. Liver-to-lesion contrast and contrast-to-noise ratios were also significantly higher after ACE-MBCA enhancement. All visualization parameters of ACE-MBCA were comparable to those of gadobenate dimeglumine, with no significant differences.

CONCLUSIONS

Compared with unenhanced MRI, ACE-MBCA MRI resulted in superior visualization and a greater number of detected liver lesions. ACE-MBCA and gadobenate dimeglumine performed similarly in the visualization and detection of colorectal liver metastases.

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.

Photon-Counting Computed Tomography: Experience in Musculoskeletal Imaging

Since the emergence of the first photon-counting computed tomography (PCCT) system in late 2021, its advantages and a wide range of applications in all fields of radiology have been demonstrated. Compared to standard energy-integrating detector-CT, PCCT allows for superior geometric dose efficiency in every examination. While this aspect by itself is groundbreaking, the advantages do not stop there. PCCT facilitates an unprecedented combination of ultra-high-resolution imaging without dose penalty or field-of-view restrictions, detector-based elimination of electronic noise, and ubiquitous multi-energy spectral information. Considering the high demands of orthopedic imaging for the visualization of minuscule details while simultaneously covering large portions of skeletal and soft tissue anatomy, no subspecialty may benefit more from this novel detector technology than musculoskeletal radiology. Deeply rooted in experimental and clinical research, this review article aims to provide an introduction to the cosmos of PCCT, explain its technical basics, and highlight the most promising applications for patient care, while also mentioning current limitations that need to be overcome.

Iodine quantification of renal lesions: Preliminary results using spectral-based material extraction on photon-counting CT

Objectives

To assess the range of quantitative iodine values in renal cysts (RC) (with a few renal neoplasms [RNs] as a comparison) to develop an expected range of values for RC that can be used in future studies for their differentiation.

Material and Methods

Consecutive patients (n = 140) with renal lesions who had undergone abdominal examination on a clinical photon-counting computed tomography (PCCT) were retrospectively included. Automated iodine quantification maps were reconstructed, and region of interest (ROI) measurements of iodine concentration (IC) (mg/cm3) were performed on whole renal lesions. In addition, for heterogeneous lesions, a secondary ROI was placed on the area most suspicious for malignancy. The discriminatory values of minimum, maximum, mean, and standard deviation for IC were compared using simple logistic regression and receiver operating characteristic curves (area under the curve [AUC]).

Results

A total of 259 renal lesions (243 RC and 16 RN) were analyzed. There were significant differences between RC and RN for all IC measures with the best-performing metrics being mean and maximum IC of the entire lesion ROI (AUC 0.912 and 0.917, respectively) but also mean and minimum IC of the most suspicious area in heterogeneous lesions (AUC 0.983 and 0.992, respectively). Most RC fell within a range of low measured iodine values although a few had higher values.

Conclusion

Automated iodine quantification maps reconstructed from clinical PCCT have a high diagnostic ability to differentiate RCs and neoplasms. The data from this pilot study can be used to help establish quantitative values for clinical differentiation of renal lesions.