Early diagnosis of prostate cancer improves its prognosis [1, 2], while screening tools should be further upgraded [10, 11, 14, 15]. Therefore, the present study aimed to explore the value of the novel functional MRI technique, APT-weighted MRI, combined with serum PSA levels for differentiating malignant prostate lesions from benign prostate lesions. The results indicated that APTmax, APTmean, ADCmean, ADCmax, ADCmin, tPAD, FPSA, FPSA/tPSA, and PSAD had a high clinical value in differentiating malignant prostate lesions from benign prostate lesions. The combination of APTmax, APTmean, ADCmean, and PSAD showed the highest diagnostic value.
Early diagnosis has important clinical significance for the treatment and prognosis of patients with prostate cancer. Nevertheless, the early differentiation of malignant prostate lesions from benign prostate lesions is still difficult in clinical practice based only on the current imaging methods, such as ultrasound and MRI. The APT imaging technique is based on transferring the amide protons and water, and it reflects the changes of proteins and pH values by variations of water signals. The internal contrast is acquired by measuring the water signals to indirectly acquire the APT-weighted signal values, depending on the exchange ratio between the amide protons and free-water protons. The exchange ratio depends on pH values and protein concentrations in the body. The APT technique was initially used for the nervous system [24,25,26]. In recent years, a great number of researchers have applied the APT technique to diagnose prostate diseases [27, 28].
The findings of the present study showed that APTmax had a high diagnostic value for differentiating malignant prostate lesions from benign prostate lesions. The sensitivity was the highest, indicating that the maximum transfer of amide protons and exchange ratio of water protons in a lesion could sensitively reflect the occurrence of malignant lesions. Jia et al. [27], for the first time, attempted to apply the APT imaging in prostate diseases, and reported the value of this technique in differentiating malignant prostate lesions from benign prostate lesions. Takayama et al. [28] found that the APT-weighted values in prostate cancer patients with a Gleason score of 7 points were significantly higher than those of patients with other scores. These findings were generally in agreement with our results. The metabolism in malignant prostate lesions is more active than in benign lesions. The exchange ratio of protons is higher, which is consistent with the pathological features of malignant lesions. The differences of APTmax and APTmean, two parameters acquired by APT imaging, were statistically significant. In contrast, the difference of APTmin was not statistically significant, which could be associated with the fact that APTmin expresses the lowest value of protein content in the region of interest, and the difference is not enough to distinguish between benign and malignant lesions. Importantly, the minimum exchange ratio of protons could not reflect the degree of metabolic activity.
The results of the present study revealed that the differences of APTmax, APTmean, ADCmean, ADCmax, ADCmin, tPAD, FPSA, FPSA/tPSA, and PSAD were statistically significant (P < 0.05), suggesting that these parameters had high diagnostic values in differentiating malignant prostate lesions from benign prostate lesions. Among these parameters, ADCmean had the highest AUC, APTmax had the highest sensitivity, and FPSA had the highest specificity and the lowest sensitivity, reflecting that FPSA had the highest diagnostic accuracy and a relatively high false-negative rate. This indicated that functional MRI sequences, such as DWI and PSA, can be used as independent predictive biomarkers to discriminate benign prostate lesions and malignant prostate lesions. In contrast, APTmax had the highest positive rate. After combining these parameters, the results showed that the combination of APTmax, APTmean, ADCmean, and PSAD had the highest AUC and sensitivity, suggesting that this combination had the highest diagnostic value for prostate cancer. Compared with using PSA and DWI alone, the combination of APT, DWI, and PSA techniques had a relatively high diagnostic value (AUC: 0.880) and a high sensitivity (86.540) for prostate cancer. A previous study demonstrated that the AUC values for the biparametric MRI (bpMRI) and multiparametric MRI (mpMRI) protocols for prostate cancer were comparable (0.790 [0.732–0.840] and 0.791 [0.733–0.841], respectively) [29]. Guo et al. [12] found that APTmean and ADC were independent predictors of TZ prostate cancer. Moreover, combination of APTmean and ADC values improved the sensitivity of the diagnosis of TZ prostate cancer and achieved the purpose of improving the diagnostic efficiency, which are similar to the results of the present study.
The advantage of APT-weighted MRI is that it is a 3D imaging technique. Compared with the conventional two-dimensional (2D) APT technique [30], this technique could scan multiple layers in a short time, acquire the APT image of the whole prostate region, and provide more comprehensive functional information.
There were several limitations in the present study. First, the sample size was small and imbalance, and additional studies are required to determine the exact diagnostic value of APT for prostate cancer. Second, this was a single-center study, and local practice biases could influence the results. Multicenter studies can not only increase the sample size, but also mitigate the risk of bias. Last but not least, because of the small sample size, no direct comparison was performed among imaging techniques.