Horst, Kelly K.

Abstract 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.

INTRODUCTION: While focal-occult placenta accreta spectrum (PAS) is known to lead to adverse outcomes, little is known of the morbidity in comparison to previa-associated PAS. METHODS: After IRB approval, retrospective review was conducted of pathologically confirmed (decidual layer absence or basal-plate myometrial fibers) PAS from 2018 to 2021 at a tertiary care center. Baseline characteristics and surgical, obstetric, and subsequent pregnancy outcomes were recorded. Focal-occult PAS was compared with previa-associated PAS using Kruskal-Wallis/Chi-square tests; P<.05 was considered significant. RESULTS: A total of 56 cases were identified: 22 previa-associated and 34 focal-occult PAS. All patients with previa-associated and 26.5% of those with focal-occult PAS underwent hysterectomy. Of the previa-associated PAS patients, 20 of 22 were diagnosed antenatally, as was 1 of 34 focal-occult PAS patients. Mean maternal age (32.5 vs. 33.1 year), number of previous dilation and curettage procedures (0.4 vs. 0.3), and in vitro fertilization rates (4.5% vs. 23.5%) were not significantly different between groups. Mean parity (3.7 vs. 1.4), gestational age at delivery (34.3 vs. 35.7 weeks), any previous cesarean delivery (95.5% vs. 29.4%), mean number of previous cesareans (2.5 vs. 0.5), and placental locations were significantly different between groups. All measures of morbidity, including postpartum hemorrhage rates (81.0% vs. 75.8%), median qualitative blood loss (1,500cc, range: 500–9,516cc vs. 1,660cc, range: 350–12,220cc), mean units of red blood cells transfused (1.8 vs. 1.9), massive transfusion (9.1% vs. 20.6%), ICU admission (9.1% vs. 14.7%), and reoperation rates (9.1% vs. 32.4%) were similar between groups. Six focal-occult PAS patients had a subsequent pregnancy, and two had recurrent PAS. CONCLUSION: Despite representing lower grade PAS, focal-occult PAS has similar measures of morbidity when compared to previa-associated PAS, potentially attributable to lack of antenatal detection.