Editorial for “Amide Proton Transfer‐Weighted Imaging Could Complement Apparent Diffusion Coefficient for More Lesion Characterization in Transition Zone of the Prostate”

Editorial for “Amide Proton Transfer-Weighted Imaging Could Complement Apparent Diffusion Coefficient for More Lesion Characterization in Transition Zone of the Prostate” Amide proton transfer-weighted (APTw) imaging, a type of chemical exchange-dependent saturation transfer (CEST) imaging, is a protein-based molecular magnetic resonance imaging (MRI) technique. Early clinical data have demonstrated that APTw imaging adds important value to the standard clinical MRI sequences in brain cancer diagnosis. Notably, APTw hyperintensity may be used as a surrogate marker for malignancies, allowing the accurate identification of the most malignant regions within heterogeneous gliomas. Recently, a panel of experts in the field has proposed consensus recommendations for APTw imaging of brain tumors. In addition to brain tumors, APTw imaging has been successfully applied to several other neurological disorders and body cancers and other diseases. There have been a few attempts to apply APTw MRI to patients with prostate cancer (PCa) to date. Jia et al were the first to evaluate the feasibility and capability of APTw imaging for the detection of PCa. They found that APTw signal intensities were significantly higher in PCa than in the peripheral zone (PZ) benign regions (N = 12). Takayama et al analyzed APTw data from 66 biopsy-proven PCas and found that the mean APTw signal intensity in PCa with a Gleason score (GS) of 7 was higher than those for the other GS groups and for noncancerous PZ tissue. Yin et al analyzed diffusion kurtosis imaging (DKI) and APTw imaging data of 49 patients with PCa and 51 patients with benign prostatic hyperplasia (BPH), showing that both DKI and APTw imaging had good and moderate correlations with GS. All of these previous studies were performed on 3 T MRI systems, and single-slice APTw imaging protocols were used. In this issue of JMRI, Guo et al evaluated whether three-dimensional APTw imaging provides new diagnostic values for transition zone (TZ) PCa. Fifty-one TZ PCa patients (age, 49–89), 44 stromal BPH (age, 57–92), and 45 glandular BPH patients (age, 56–92) were included and scanned at 3 T. It is shown that APTw intensities were significantly different between TZ PCa and stromal BPH or glandular BPH, but not between stromal BPH and glandular BPH. The authors hypothesized that the tight arrangement of cells, the reduction of intercellular space, and the increase of macromolecules and peptides secreted by TZ PCa could result in higher APTw. It is concluded that APTw imaging can provide an added value to apparent diffusion coefficient (ADC) in the identification of TZ PCa from BPH and stromal BPH. When looking into these studies, the currently used APT imaging pulse sequence types/parameters and acquisition protocols vary substantially among labs, far from being optimized. A main reason is that the APT experimental parameters (particularly amplifier duty cycle and saturation pulse length) are often limited by scanner hardware constraints. Further, to quantify more pure APT signals in vivo, more complicated APT imaging acquisition or analysis approaches have been proposed. It would be important to evaluate the use of other APT imaging metrics in PCa, in addition to APTw. Notably, Evans et al optimized an acquisition and postprocessing protocol for multipool CEST fitting analysis of prostate data and evaluated the repeatability of the technique. Their optimized saturation scheme was found to be 60 sinc-Gaussian pulses with 40 msec pulse duration, at 50% duty-cycle with continuous-wave pulse equivalent B1 power of 0.92 μT. However, it is known that the low duty-cycle (50%) used in this study has inherently low APTw signal intensities. Similar to neuro applications, there is a need to develop an optimized and standardized approach for imaging