Longitudinal anatomical and metabolic MRI characterization of orthotopic xenograft prostate tumors in nude mice

Abstract

MRI using the balanced steady-state free precession (bSSFP) sequence can be used to monitor tumor growth in orthotopic PC-3M tumors as early as 9 days post-injection. Hyperpolarized pyruvate MRI has potential to assess tumor metabolism and necrosis.

In Vivo 3D MRI Measurement of Tumour Volume in an Orthotopic Mouse Model of Prostate Cancer

“…Additionally, MRI allows for the measurement of parameters other than volume: Mallett et al showed that hyperpolarized (HP) 13 C magnetic resonance spectroscopic imaging (MRSI) has the potential to assess tumor metabolism and necrosis of orthotopic xenografts in a CaP nude mice model. 5 Using the same technique, Aggarwal et al demonstrated that HP 1-[ 13 C]-pyruvate MRSI could detect the metabolic changes within the prostate tumor as early as 6 weeks after the initiation of androgen deprivation therapy, while there was no such a response that could be ascertained using standard MRI. 21…”

“…Previous studies have used both gradient echo (GRE)-based and spin-echo-based MRI methods to detect and delineate CaP. Using balanced steady-state free precession sequences, Mallett et al showed that GRE-based MRI can successfully monitor tumor growth in orthotopic PC-3M tumors, 5 and Li et al have studied visibility of CaP, with the finding that visibility in these methods depends on gene expression in the tumor. 3 Previously, spin-echo-based sequences have been used which (due to the refocusing of static inhomogeneities) generally provide better stability in abdominal regions but often come with the downside of long scan times.…”

“…To minimize susceptibility artefacts and signal dephasing in the heterogenous abdominal region, we optimized a 2D FSE (TurboRARE) sequence. In contrast to gradient echo techniques which are commonly used in such studies, 5 the spin-echo-based method refocuses effects from static spin dephasing while still maintaining high temporal efficiency by using an echo train of refocusing pulses. The sequence was optimized for best T2 contrast and low artefacts (from susceptibility and fat shifts) specifically in the tissues inside and surrounding the prostate tumor while still maintaining high signal-to-nosie ratio (SNR) and good tumor delineation using the following general imaging parameters: Echo Time (TE) = 21 milliseconds, Repetition Time (TR) = 2177 milliseconds, Bandwidth (BW) = 80000 Hz, Echo Train Length (ETL) = 8, slice thickness = 500 mm, field of view 30 × 30 mm, matrix size 192 × 192, in-plane resolution 156 × 156 µm, 30 slices, and total acquisition time 11 minutes.…”

“…3 Ravoori et al used T2-based Dixon “water only” sequence to clearly visualize the mouse prostate gland in young and old mice 4 ; it was also reported by Mallett et al that MRI using the balanced steady-state free precession sequence could identify prostate tumors both anatomically and functionally. 5 In order to clearly detect extracapsular prostate tumor extension which is surrounded by the periprostatic fat, fat suppression techniques such as chemical shift-selective (CHESS) pulse have been developed to repress the signal from the fat. 6,7…”

In Vivo Magnetic Resonance Imaging of Orthotopic Prostate Cancer

“…Imaging would allow identification of animals with tumors and exclude those without, thus reducing the number of animals needed to assess the effect of an intervention. Commonly, T1-or non-fat-suppressed T2-weighted MRI, and less commonly diffusion-weighted imaging, has been used for detecting and monitoring large prostate tumors in mice, commonly without any significant adjacent normal prostate tissue [7,12,13,[16][17][18].…”