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

Murali Ravoori,Wei Wei,Vikas Kundra,Ping Liu,Mihai Gagea,Sheela Singh,Jyoti Duggal,Lin Han,Jingfei Ma,James A Bankson,Dustin K Ragan,Ming Tat Ling

doi:10.1371/journal.pone.0055746

Abstract

PurposeProstate 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.TechniqueMagnetic 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.ResultsT2-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).ConclusionT2-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.

Highlights

Prostate research has been limited by a dearth of methods for visualizing the gland in animal models [1,2,3,4,5]
Prostate T2 Fast spin echo (FSE) as well as proton density-based and T2based-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)
Compared to the other modalities, the spatial resolution and contrast of MR enables exquisite anatomic depiction. Both image contrast and spatial resolution are influenced by field strength

Summary

Introduction

Prostate research has been limited by a dearth of methods for visualizing the gland in animal models [1,2,3,4,5]. Multiple other sequences have not been compared for visualizing the prostate. T1 and T2-weighted sequences are used to delineate organs, and diffusion-weighted imaging (DWI) is commonly used clinically. Newer sequences such as Dixon [9] -based sequences can be applied to obtain ‘‘water’’ weighting or ‘‘fat’’ weighting; the degree of weighting is based on the original sequence weighting such as T2 or proton density. Compared to the other modalities, the spatial resolution and contrast of MR enables exquisite anatomic depiction. Both image contrast and spatial resolution are influenced by field strength. Higher field strength has not always proved advantageous, especially for body imaging [10]

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Results

Conclusion