Fig. 2
Representative images to determine PHL tumor threshold and to measure MLPHL and MTVPHL. Step 1 (upper): PHL image settings. A segmental hypermetabolic lesion (SUVmax = 13.07) is identified in the mid esophagus (upper left). The window level is set in SUV units. The top value is set to slightly higher than SUVmax (top value 13.1 > 13.07), and the bottom value is set to zero (upper middle). Thereafter, the color scale is changed to a 10-step color scale, which was Spectrum 10 in our study (upper right). A magnified view is used to determine background activity and PHL. Magnification of the ESCC (red dotted box) is performed. Step 2 (middle): Magnified view of the ESCC using PHL image settings (red dotted box in the upper right image). In this image, each layer represents 10% of SUVmax. The hottest core is > 90% of SUVmax. There are two hot cores in this ESCC. PHL is located between the tumor and the background activity. In this image, the background activity is the dark blue layer (10–20% of SUVmax), and the PHL is located at 20–30% of SUVmax (light blue layer; red arrows). Therefore, the PHL tumor threshold is 30% of SUVmax (i.e., the innermost portion of the PHL; red dotted arrow). Layer thickness increases abruptly in the PHL. Step 3 (lower): Measurement of MLPHL and MTVPHL. After we determined PHL tumor threshold, we manually measured MLPHL using the ruler tool of the workstation (lower left). MTVPHL was measured by the auto-segmentation program after applying PHL tumor threshold (lower right; 30% of SUVmax in this ESCC)