Currently, magnetic resonance imaging (MRI) plays an important role in rectal cancer imaging, especially high-resolution T2-weighted imaging (T2WI), which is the key sequence due to the thin section (3 mm) and high resolution (0.5–0.8 mm) [1]. High-resolution T2WI allows the evaluation of tumor margins in relation to rectal wall layers, lymph nodes on the wall, and lymph nodes on the superior rectal and pelvic sidewall and reveals the relationship of the tumor to the circumferential resection margin [1]. The axial T2WI can be obtained orthogonally to the tumor surface detected by the sagittal fast spin-echo (FSE) T2WI plane if the tumor is obvious. However, the tumor may be difficult to identify on sagittal images if it is small in size or if there is an intrinsic low contrast between the tumor and the rectal wall in FSE T2WI. It was time-consuming that the whole rectum was scanned with axial high-resolution high-resolution T2WI due to the use of thin sections and high in-plane resolution. The use of T2 images might be useful in exploring new imaging-based biomarkers, such as radiomics [2], [3]. Thus, a better strategy would provide contrasting differences in signal intensity between tumor and normal tissue before the T2WI scan for better rectal cancer detection.

Diffusion-weighted imaging (DWI), as a functional MRI component, is constructed by quantifying the diffusion of water molecules in tissues [4], [5]. In malignant lesions, diffusion is often restricted due to greater cellularity, tissue disorganization, and disorganization, and decreased extracellular space, generating hyperintensity in DWI [4], [5], [6], [7]. The b-value is the essential parameter that can affect the tumor detection capacity in DWI [8], [9], [10], [11], [12], [13]. Several studies have demonstrated that conventional high b-value (800–1000 sec/mm2) DWI is useful for locating rectal tumors during primary staging [14], [15], [16], [17]. However, some normal structures such as the small intestine, prostate, seminal vesicles, and endometrium remained hyperintense with a conventional high b-value of 1000 sec/mm2 DWI [14], leading to false positive cases, which could lead to false-positive cases when qualitatively assessed with the naked eye. The promising strategy to further improve the precision of rectal cancer examination is to use the higher b-value b (1,400–2000 sec/mm2 or higher) DWI. Higher b-value DWI would improve the contrast between cancerous and noncancerous tissue in visual assessment [9], [10], [11], [12]. Several studies have confirmed that diagnosis with a higher b-value (1500–4500 sec/mm2) is superior to that of conventional lower b-value (1000 sec/mm2) DWI in glioma and prostate cancer [8], [9], [10], [11], [12]. To our knowledge, such research is rare in the detection of rectal cancer.

The apparent diffusion coefficient (ADC), a quantitative value of DWI, has been reported to correlate with histological grade, aggressiveness and aggressiveness, and clinical outcome of rectal cancer [16], [17], [18], [19], [20], [21]. However, the average value of the ADC may underestimate the biological significance of ADC in a heterogeneous tumor with variable cellularity [16]. Histogram analysis is a method that can provide statistical data and quantitative information on tumor heterogeneity [22]. When covering the entire lesion area, the promising sampling bias has been removed, and tumor components illustrating the different characteristics of diffusion will be demonstrated or reflected in the histogramgraph [22]. ADC-histogram analysis has been applied to differentiate the focal pancreatic lesion [22], assess the response of locally advanced rectal cancer to chemotherapy [23], [24], [25], [26], and determine the aggressiveness of cervical cancer [27], [28], [29]. A brain study reported that the diagnostic performance of the low percentile of the ADC histogram obtained from the b-value the b-value for the 3,000 sec/mm2 DWI is superior to that of the b-value the b-value for the 1000 sec/mm2 DWI [30].

Thus, this research aimed to assess the potential b-value for 2000 sec/mm2 DWI imaging in the ability to detect rectal cancer and the diagnosis of ADC-histogram analysis in identifying early-stage tumors, compared to the b-value for 1000 sec/mm2 DWI.