Role of imaging in evaluating the response after neoadjuvant treatment for pancreatic ductal adenocarcinoma

Table 1 Role of current imaging in the response assessment after neoadjuvant treatment for pancreatic ductal adenocarcinoma

Imaging technologies	Imaging parameters	Pathological basis	Roles and advantages	Limitations	Improvement
US	Conventional US imaging features	Iso-/low-attenuating pancreatic masses	Non-radiation and high economy; a tool for PDAC early detection and staging; detection of systemic therapies associated adverse events in metastatic PDAC	Play the limited role for tumor response of PDAC after NAT	Further exploration
EUS	Tumor size	Change in tumor size after NAT	Provides additional information for response assessment and survival prediction	Invasive procedure, preliminary research, lack of credible results	Further large-scale research is needed in the future
	Tumor stiffness (EUS elastography)	Decrease of change in tumor stiffness after NAT	Potential marker for NAT response and tumor resectability assessment	Poor objectivity and low reproducibility; the pressure of the probe on the lesion area is not easily controlled	Technology Optimization; further investigation is needed
CT	MDCT conventional imaging features Tumor size; Enhancement; Tumor-vessel contact	Size or enhancement reduction; changes in tumor-vessel contact	High-density resolution; speed of data acquisition; multiplanar reconstruction ability	Low specificity and sensitivity (53%-80% of patients are in a stable state on MDCT after NAT)	Further quantification, exploration and evaluation of imaging indicators on MDCT conventional imaging features
	Perfusion CT; Blood flow; Blood volume Permeability–surface area product	Changes in extracellular matrix causing changes in the tumor blood flow	Pre-treatment perfusion CT can be helpful to predict the histopathologic response of PDAC to NAT	Preliminary research, lack of credible results	Further studies are needed to evaluate the value of perfusion imaging in a large number of patients
	Texture analysis; Texture features	CT texture features after NAT can reveal the heterogeneity in PDAC	Providing additional value for judging tumor heterogeneity; judging tissue changes and tumor downstaging in those cases with no significant alteration in tumor size after NAT	Time consuming segmentation and non-robustness conclusion	Further large-scale research is needed in the future
	Radiomics; Radiomics features and delta radiomics features combined with common clinical index (e.g., CA-199)	Radiomics features after NAT can reveal the heterogeneity change of PDAC	Increasing the possibility for response-based treatment adaptation; has a broad prospect in the management of PDAC after NAT	The lack of enough research; time consuming segmentation and non-robustness conclusion
MRI	ADC value of DWI	Cellularity and potential fibrotic changes of PDAC after NAT	Improve the prediction possibility of R0 resection rate (75% accuracy) in resectable PDAC; pre-treatment ADC can be used to distinguish responding patients from non-responding patients after NAT	Few related studies and inconsistent conclusions; no unified standard for the selection of DWI scanning technology and parameters; large motion artifacts, time-consuming and high cost	Large-scale studies to validate the role of DWI in PDAC to NAT; establish a unified scanning standard; reduce motion artifacts and scan time; reduce costs by optimizing sequences
PET imaging	SUVmax	Changes in glucose metabolism of tumors before and after NAT	Aid in monitoring the clinical outcome of patients with locally advanced PDAC treated with NAT; distinguish responding patients from non-responding patients after NAT; plays a significant role in the clinical decision-making of patients	Lack of relevant research and high cost of inspection	Application of PERCIST criteria and comparison with the accuracy of traditional evaluation criteria will be the future research direction

ADC: Apparent diffusion coefficient; CT: Computed tomography; DWI: Diffusion-weighted imaging; EUS: Endoscopic ultrasound; MRI: Magnetic resonance imaging; NAT: Neoadjuvant treatment; PDAC: Pancreatic ductal adenocarcinoma; PERCIST: Positron emission tomography response criteria in solid tumor; PET: Positron emission tomography; SUV: Standardized uptake value; US: Ultrasound.