In order to produce an actual image of T₁, as opposed to one that is merely T₁-weighted, it is necessary to take at least two separate images and use them to compute a pixel-by-pixel estimate of T₁.

(a) Show that the imaging equation in (13.63) can be written as

(b) Assume that three images f1, f2, and f3 with tip angles α₁, α₂, and α₃, respectively, are acquired. Show that the points (f_i/ tan α_i, f_i/ sin α_i), i = 1, 2, 3, should lie on a line.

(c) Using the fact shown in part (b), find a closed-form expression for an estimate of T₁ given only two images f₁ and f₂ with different tip angles α₁ and α₂.