In vivo micro-CT imaging of untreated and irradiated orthotopic glioblastoma xenografts in mice: capabilities, limitations and a comparison with bioluminescence imaging

Abstract

Small animal imaging is of increasing relevance in biomedical research. Studies systematically assessing the diagnostic accuracy of contrast-enhanced in vivo micro-CT of orthotopic glioma xenografts in mice do not exist. NOD/SCID/γc(-/-) mice (n = 27) underwent intracerebral implantation of 2.5 × 10(6) GFP-Luciferase-transduced U87MG cells. Mice underwent bioluminescence imaging (BLI) to detect tumor growth and afterwards repeated contrast-enhanced (300 µl Iomeprol i.v.) micro-CT imaging (80 kV, 75 µAs, 360° rotation, 1,000 projections, 33 s scan time, resolution 40 × 40 × 53 µm, 0.5 Gy/scan). Presence of tumors, tumor diameter and tumor volume in micro-CT were rated by two independent readers. Results were compared with histological analyses. Six mice with tumors confirmed by micro-CT received fractionated irradiation (3 × 5 Gy every other day) using the micro-CT (5 mm pencil beam geometry). Repeated micro-CT scans were tolerated well. Tumor engraftment rate was 74 % (n = 20). In micro-CT, mean tumor volume was 30 ± 33 mm(3), and the smallest detectable tumor measured 360 × 620 µm. The inter-rater agreement (n = 51 micro-CT scans) for the item tumor yes/no was excellent (Spearman-Rho = 0.862, p < 0.001). Sensitivity and specificity of micro-CT were 0.95 and 0.71, respectively (PPV = 0.91, NPV = 0.83). BLI on day 21 after tumor implantation had a sensitivity and specificity of 0.90 and 1.0, respectively (PPV = 1.0, NPV = 0.5). Maximum tumor diameter and volume in micro-CT and histology correlated excellently (tumor diameter: 0.929, p < 0.001; tumor volume: 0.969, p < 0.001, n = 17). Irradiated animals showed a large central tumor necrosis. Longitudinal contrast enhanced micro-CT imaging of brain tumor growth in live mice is feasible at high sensitivity levels and with excellent inter-rater agreement and allows visualization of radiation effects.

Imaging of Orthotopic Glioblastoma Xenografts in Mice Using a Clinical CT Scanner: Comparison with Micro-CT and Histology

“…Improvements in micro-CT imaging did not only allow to visualize brain vessels (for e.g. studies on stroke and vasospasm) [17, 22], but also to detect brain tumors in animals as small as mice [6, 51]. Compared to micro-CT scanners, the use of clinical CT scanners for brain tumor imaging in mice has been considered critical due to the limited spatial resolution.…”

“…All mice (n = 9) were anesthesized by subcutaneous injection with a mixture of medetomidine (0.5 mg/kg), midazolam (5 mg/kg) and fentanyl (0.05 mg/kg). Implantation of tumor cells was performed as described recently [6, 27]. Prior to surgery the animals received a subcutaneous injection of sodium chloride (10 ml/kg) to prevent dehydration.…”

“…Even in small rodents like mice, noninvasive imaging techniques have been established to monitor disease development, progression and treatment effects in brain tumor models. Dedicated small animal magnetic resonance (MR) scanners [2–5], micro-computed tomography (micro-CT) [6–10], positron emission tomography/single-photon emission computed tomography (PET/SPECT) [2, 7, 9, 10], and bioluminescence imaging (BLI) [2, 4, 5, 11, 12] have been used for imaging of glioma growth in living mice. As these modalities are not ubiquitously available, clinical MR scanners have also been succesfully used for imaging of murine brain tumors [13, 14].…”

“…Nevertheless, micro-CT has been successfully used for the evaluation of anatomical structures (e. g. vascular imaging, virtual colonoscopy) and pathological processes (e.g. intrahepatic, intrasplenic and intracerebral tumor growth) in animals as small as mice [6, 15–23]. Clinical scanners to some point are an alternative to dedicated small animal scanners as they are ubiquitously available and allow fast, easy and cost effective visualization of anatomical structures and some disease processes [24–26].…”

Targeted gene therapy and in vivo bioluminescent imaging for monitoring postsurgical recurrence and metastasis in mouse models of liver cancer

“…Moreover, the treatment course could not be monitored in real time, and the effectiveness of the treatment could only be evaluated by killing the model animals. In the current study, OIIT was used to perform rapid, intuitive, and quantitative real-time monitoring, which avoided selection differences and allowed us to observe tumor growth at any time, so that scientific conclusions could be made on the treatment results (Kirschner et al, 2015).…”