Multi‐system evaluation of baseline‐referenced gray scale CNR profile deviation for phantom‐based ultrasound quality assurance

BACKGROUND: Phantom-based ultrasound quality assurance (QA) commonly incorporates qualitative image assessment, whereas robust baseline-referenced quantitative indicators for routine monitoring across multiple systems remain limited. PURPOSE: To investigate whether controlled transducer surface acoustic shielding produces measurable baseline-referenced changes in selected dead zone (DZ) and gray scale (GS) indicators across multiple ultrasound systems using an ATS-539 phantom. METHODS: Four ultrasound systems (GE LOGIQ P10, GE LOGIQ P6, Mindray DC-70 Exp, and Siemens X150) were evaluated. The transducer aperture was partially shielded with insulating tape at 0%, 5%, 10%, 15%, 20%, and 30% coverage, applied either centrally or at the indicator-side margin. Five repeated images were acquired for each condition. GS performance was assessed using the contrast-to-noise ratio (CNR) of six cylindrical targets. Target-specific CNR values were converted to within-device z-deviations relative to baseline (L0), and the root-mean-square z-deviation across all six targets (RMS-z) was used as the primary GS profile indicator. DZ performance was evaluated using landmark-based pin brightness as a secondary near-field indicator. RESULTS: Under central shielding, the GS RMS-z profile deviation score increased with shielding ratio in all four systems (Spearman ρ = 0.642-0.975, all p < 0.001). Central shielding produced consistent RMS-z increases across all four systems, whereas indicator-side shielding yielded a more heterogeneous response: RMS-z remained positively associated with shielding ratio in three systems (ρ = 0.734-0.917, all p < 0.001), but the response was weaker and non-significant in the GE LOGIQ P10. Central DZ pin brightness decreased with increasing shielding ratio across all systems (ρ = -0.581 to -0.865, all p < 0.001). Baseline CNR profiles and absolute CNR magnitudes differed substantially among systems, and within-device baseline referencing was therefore preferred over direct cross-system comparison. Manual landmark placement demonstrated high repeatability for target-specific CNR and DZ brightness measurements (ICC(A,1) = 0.88-0.97), whereas the aggregate RMS-z score showed moderate-to-good repeatability (ICC(A,1) = 0.771). CONCLUSIONS: Baseline-referenced GS CNR profile deviation demonstrated a consistent response to controlled acoustic shielding across multiple ultrasound systems. DZ brightness provided complementary near-field information but remained a secondary indicator. These findings support device-specific longitudinal monitoring of phantom-based QA metrics rather than interpretation based on universal cutoff values.