Campeau, Norbert G

Abstract Photon-counting detector CT (PCD-CT) directly detects individual photons and measures their energies, enabling the acquisition of multi-energy data from a single x-ray source with higher spatial resolution, thereby allowing visualization of smaller arteries and veins and other important imaging features not seen at conventional CT. It also substantially reduces calcium and stent blooming artifacts. Appropriate patient selection and task-based optimization of acquisition, reconstruction, and interpretation are critical to realize these benefits. Vascular imaging examinations for which early evidence shows that PCD-CT demonstrates higher diagnostic performance compared to conventional CT include coronary CT angiography (CTA) for evaluation of partially calcified plaques or stents, peripheral runoff CTA, detection of cerebrospinal fluid-venous fistulas, and head CTA for evaluation of small intracranial vessels and aneurysms. Current limitations include excessive image noise with the sharpest reconstruction kernels and challenges when adapting conventional CT protocols (eg, requiring sharper kernels, thinner slices, higher matrices, tailored scan modes) to achieve time-efficient image reconstruction and hanging protocols. New solutions and directions will include deep-learning-based image noise reduction, improved spectral separation, strategic triage of specific patient populations to PCD-CT systems, and subspecialty clinical practice recommendations for this new technology.

Purpose: To evaluate the performance of a new, highly flexible radiofrequency (RF) coil system for imaging patients undergoing MR simulation. Methods: Volumetric phantom and in vivo images were acquired with a commercially available and prototype RF coil set. Phantom evaluation was performed using a silicone-filled humanoid phantom of the head and shoulders. In vivo assessment was performed in five healthy and six patient subjects. Phantom data included T1-weighted volumetric imaging, while in vivo acquisitions included both T1- and T2-weighted volumetric imaging. Signal to noise ratio (SNR) and uniformity metrics were calculated in the phantom data, while SNR values were calculated in vivo. Statistical significance was tested by means of a non-parametric analysis of variance test. Results: At a threshold of p = 0.05, differences in measured SNR distributions within the entire phantom volume were statistically different in two of the three paired coil set comparisons. Differences in per slice average SNR between the two coil sets were all statistically significant, as well as differences in per slice image uniformity. For patients, SNRs within the entire imaging volume were statistically significantly different in four of the nine comparisons and seven of the nine comparisons performed on the per slice average SNR values. For healthy subjects, SNRs within the entire imaging volume were statistically significantly different in seven of the nine comparisons and eight of the nine comparisons when per slice average SNR was tested. Conclusions: Phantom and in vivo results demonstrate that image quality obtained from the novel flexible RF coil set was similar or improved over the conventional coil system. The results also demonstrate that image quality is impacted by the specific coil configurations used for imaging and should be matched appropriately to the anatomic site imaged to ensure optimal and reproducible image quality.

Background Dental hardware produces streak artifacts on computed tomography (CT) images reconstructed with the standard weighted filtered back projection (wFBP) method. Purpose To perform a preliminary evaluation of an iterative metal artifact reduction (IMAR) technique to assess its ability to improve anatomic visualization over wFBP in patients with dental amalgam or other hardware. Material and Methods CT images from patients with dental hardware were reconstructed using wFBP and IMAR software and soft-tissue or bone window/level settings. The anatomy most affected by metal artifacts was identified. Two neuroradiologists determined subjective and objective imaging features, including overall metal artifact score (1 = severe artifacts, 5 = no artifacts), soft-tissue visualization score of the most-compromised structure, and artifact length along the skin surface. CT numbers were used to quantify artifact severity. Results Twenty-four patients were included. IMAR improved overall metal artifact score in 18/24 cases (median =2 ± 0.9 vs. 1 ± 0.6, P < 0.001). Mean CT number in the most-affected anatomical structure significantly improved with IMAR (94.6 vs. 219 HU, P = 0.002) and length of affected skin surface decreased (40.4 mm vs. 118.7 mm, P < 0.001). However, osseous/dental artifactual defects were found in 22/24 cases with IMAR vs. 11/24 with wFBP. Conclusion IMAR software reduced metal artifact both subjectively and objectively and improved visualization of adjacent soft tissues. However, it produced a higher rate of artifactual defects in the teeth and bones than wFBP. Our findings support the use of IMAR as a valuable complement to, but not a replacement for, standard wFBP image reconstruction.

A 67-year-old male presented to the emergency department with concern for accidental aspiration of an aluminum beverage can pull tab. Neck and chest radiographs did not reveal an aspirated foreign body. Despite ongoing complaint of dysgeusia and adamancy of aspiration by the patient, he was discharged to home without recommendation for further follow-up. Seven months later, a computed tomography (CT) scan of the chest performed as part of an unrelated lung cancer work up confirmed the presence of a left mainstem bronchus metallic foreign body compatible with a pull tab. This case report illustrates the poor negative predictive value of radiographs for a suspected aluminum foreign body and demonstrates the superiority of CT for this purpose. In such presentations it is imperative to have a low threshold for performing further diagnostic evaluation with CT due to the relatively high radiolucency of aluminum.

Although more prevalent in males in the 6th and 7th decade of life, spinal dural arteriovenous fistulas (SDAVFs) are an uncommon cause of progressive myelopathy. Magnetic resonance imaging and more recently Gd bolus MR angiography have been used to diagnose, radiographically define, and preprocedurally localize the contributing lumbar artery. Three-dimensional myelographic MR imaging sequences have recently been developed for anatomical evaluation of the spinal canal. The authors describe 3 recent cases in which volumetric myelographic MR imaging with a 3D phase-cycled fast imaging employing steady state acquisition (PC-FIESTA) and a 3D constructive interference steady state (CISS) technique were particularly useful not only for documenting an SDAVF, but also for providing localization when CT angiography, MR imaging, MR angiography, and spinal angiography failed to localize the fistula. In a patient harboring an SDAVF at T-4, surgical exploration was performed based on the constellation of findings on the PC-FIESTA images as well as the fact that the spinal segments leading to T-4 were the only ones that the authors were unable to catheterize. In a second patient, who harbored an SDAVF at T-6, after 2 separate angiograms failed to demonstrate the fistula, careful assessment of the CISS images led the authors to focus a third angiogram on the left T-6 intercostal artery and to perform superselective microcatheterization. In a third patient with an SDAVF originating from the lateral sacral branch, the PC-FIESTA sequence demonstrated the arterialized vein extending into the S-1 foramen, leading to a second angiogram and superselective internal iliac injections. The authors concluded that myelographic MR imaging sequences can be useful not only as an aid to diagnosis but also for localization of an SDAVF in complex cases.