Visualizing the prostate gland by MR imaging in young and old mice

Abstract

Purpose: Prostate imaging requires optimization in young and old mouse models. We tested which MR sequences and field strengths best depict the prostate gland in young and old mice; and, whether prostate MR signal, size, and architecture change with age.

Technique: Magnetic resonance imaging (MRI) of the prostate of young (2 months) and old (18 months) male nude mice (n = 6) was performed at 4.7 and 7 T and SCID mice (n = 6) at 7 T field strengths, using T1, fat suppressed T1, DWI, T2, fat suppressed T2, as well as T2-based- and proton density-based Dixon "water only" sequences. Images were ranked for best overall sequence for prostate visualization, prostate delineation, and quality of fat suppression. Prostate volume and signal characteristics were compared and histology was performed.

Results: T2-based-Dixon "water only" images ranked best overall for prostate visualization and delineation as well as fat suppression (n = 6, P<0.001) at both 4.7 T and 7 T in nude and 7T in SCID mice. Evaluated in nude mice, T2-based Dixon "water only" had greater prostate CNR and lower fat SNR at 7 T than 4.7 T (P<0.001). Prostate volume was less in older than younger mice (n = 6, P<0.02 nude mice; n = 6, P<0.002 SCID mice). Prostate T2 FSE as well as proton density-based and T2-based-Dixon "water only" signal intensity was higher in younger than older mice (P<0.001 nude mice; P<0.01 SCID mice) both at 4.7 and 7 T. This corresponded to an increase in glandular hyperplasia in older mice by histology (P<0.01, n = 6).

Conclusion: T2-based Dixon "water only" images best depict the mouse prostate in young and old nude mice at 4.7 and 7 T. The mouse prostate decreases in size with age. The decrease in T2 and T2-based Dixon "water only" signal with age corresponds with glandular hyperplasia. Findings suggest age should be an important determinant when choosing models of prostate biology and disease.

Figure 1. Representative MR images of the prostate gland of nude (4.7T, A), SCID (7T, B) young (top) and old (bottom) mice with different MR sequences.

Arrow indicates the prostate gland.

Figure 2. Prostate visualization, prostate border delineation, and fat suppression of young and old SCID and nude mice ranked significantly higher on T2-Dixon “water only” overall and generally better than T2 FS images using either 4.7 T or 7T scanners.

A) 7T magnet, young vs old mice (*, P<0.01, T2-Dixon vs T2 FS; #, P<0.001, T2-Dixon “water only” young vs old); B) 4.7 T vs 7T (*, P<0.01, T2-Dixon vs T2 FS; #, P<.05, T2-Dixon “water only” 4.7T vs 7T). Reader 1 data presented.

Figure 3. Prostate gland volume derived from 7T MR images of young and old SCID and nude mice (*, P<0.02, n = 6 for young vs old nude mice; P<0.002, n = 6 for young vs old SCID mice).

Figure 4. Prostate gland signal intensity measured using T2-Dixon-“water only” (A), T2 FS (B), or (C) PD-Dixon-“water only” sequences in young and old SCID and nude mice both at 4.7 T and 7T (*, P<0.05, n = 6).

Figure 5. Prostate gland histology of young and old mice, H&E stain, ×400.

A) Nude young mice, minimal hyperplasia, grade 1; B) Nude old mice, mild hyperplasia, grade 2; C) SCID young mice, minimal hyperplasia, grade 1; D) SCID old mice, moderate hyperplasia, grade 3.