Figure 3.

Detectability index computed for the five observer models in Eqs. 6, 7, 8, 9, 10 as a function of magnification and detector pixel size (a_pix). (Top row) d′(M, a_pix) for task 1 (low-frequency muscle vs water detection task). (Bottom row) d′(M, a_pix) for task 3 (high frequency muscle vs water discrimination task). The low-frequency task exhibits lower d′ overall due to background anatomical noise and is clutter-limited to a greater extent. The high-frequency task emphasizes detail and is less susceptible to clutter. Both tasks suggest highest performance at M ∼ 1.2–1.3. The low-frequency task favors large pixel size, as expected, whereas the high-frequency task demonstrates an optimum a_pix ∼ 0.1–0.2 mm.