Non-Invasive Assessment of SMAD4 Expression Status in Pancreatic Ductal Adenocarcinoma: Diagnostic Value of T1ρ-Weighted Imaging Combined with Clinical Parameters

Background/Objectives: Pancreatic ductal adenocarcinoma (PDAC) is a malignancy with poor prognosis, where SMAD4 protein loss is closely associated with increased tumor aggressiveness and metastatic potential. Current assessment of SMAD4 expression relies on IHC of tumor tissue obtained by biopsy or resection, in which limited sampling may not represent intratumoral heterogeneity. T1ρ-weighted imaging, an emerging functional MRI technique, shows promise in characterizing tumor microstructural properties. This study aimed to evaluate the value of T1ρ imaging combined with conventional MRI sequences and clinical parameters for non-invasive prediction of SMAD4 protein expression status in PDAC. Methods: This retrospective single-center study included 57 patients with histologically confirmed PDAC who underwent pretreatment MRI with T1ρ imaging between September 2024 and May 2025. Immunohistochemical analysis revealed SMAD4 intact in 28 tumors (49.1%) and SMAD4 loss in 29 tumors (50.9%). T1ρ values were measured and compared between SMAD4 intact and SMAD4 loss tumors. A multiparametric predictive model incorporating T1ρ values, lymph node metastasis status, and carbohydrate antigen 19-9 (CA19-9) levels was developed. Results: SMAD4 intact tumors demonstrated significantly higher T1ρ values compared to SMAD4 loss tumors (96.34 ± 14.12 vs. 71.93 ± 10.24 ms, p < 0.001). T1ρ achieved an AUC of 0.901 (95% CI: 0.817–0.986), with 82.14% sensitivity and 89.66% specificity, for predicting SMAD4 expression status. A multiparametric model combining T1ρ values, lymph node metastasis status, and CA19-9 levels yielded a numerically higher AUC of 0.932 (95% CI: 0.862–1.000), although the difference from T1ρ alone was not statistically significant (DeLong test, p > 0.05). Conclusions: T1ρ imaging showed potential for predicting SMAD4 status in PDAC.