Addressing Access to Advanced Diagnostic Techniques: A National Geospatial Study on SPECT-CT Imaging Access Across Geographic and Demographic Groups.

Abstract

SPECT-CT (Single Photon Emission Computed Tomography integrated with Computed Tomography) is an advanced multimodal imaging technique with established applications across musculoskeletal, oncological, and neurological indications. However, the national geographic and sociodemographic distribution of SPECT-CT access in the United States remains poorly characterized. This study aimed to build a comprehensive national database of SPECT-CT facilities, and quantify access disparities across geographic and sociodemographic dimensions. Facility data were compiled from the American College of Radiology (ACR) database as of April 2024. Demographic and socioeconomic characteristics for each ZIP Code Tabulation Area (ZCTA) were obtained from the 2021 American Community Survey. Spatial access was measured using the Two-Step Floating Catchment Area (2SFCA) method. Inequality was assessed via Lorenz curves, Gini coefficient, and Theil index. Decomposition of the Theil index was used to evaluate between- and within-group disparities by income, race, sex, and population. Geographically Weighted Regression (GWR) was used to evaluate spatial variation in the association between sociodemographic predictors and distance to the nearest SPECT-CT facility, compared against a global Ordinary Least Squares (OLS) model. A total of 1,661 SPECT-CT facilities were identified, with coastal and urban states showing higher density. Spatial access was highly unequal (Gini = 0.327; Theil = 0.205), with many ZCTAs receiving no meaningful access. Decomposition analyses revealed significant between-group inequality by race and population (p = 0.001 and 0.004), but not by income or sex. Within-group disparities were also substantial, with lower-White and high-population areas exhibiting the highest internal inequality. The GWR model demonstrated markedly better fit than OLS (adjusted R² = 0.984 vs. 0.115) and identified strong regional variation in predictor effects, including reversals in the direction of racial impact (local β for percent White: -7.82 to +9.37 miles/%). SPECT-CT access in the US is marked by stark geographic and demographic disparities, characterized by inequity across multiple axes. By improving access, we can also promote the adoption of preventative care over reactive interventions.