Detection of bromobenzene-induced hepatocellular necrosis using magnetic resonance microscopy

Biomedical imaging in the safety evaluation of new drugs

Toxicology accounts for approximately one-third of attrition in new drug development and is a major concern in the pharmaceutical industry. This paper reviews the role of biomedical imaging in the safety evaluation of new candidate drugs. Ex vivo high-resolution three-dimensional imaging of specimens can provide a quick overview of the specimens. Volumetric measurements of tissue structures and lesions can be made with higher precision and reproducibility than histology approaches. As opposed to histology, in vivo animal imaging permits longitudinal studies of the same animals over an extended period of time, with individual animals serving as their own control. Therefore, the number of animals required for a study can be significantly reduced and the intra-subject variability is minimized. Repeated in vivo imaging allows monitoring of the occurrence and progression, or regression, of various structural and functional abnormalities. Compared with other biological assays, imaging can provide anatomically specific information about tissue abnormality. Imaging offers the opportunity to carry forward the same methodology in animal experiments into human studies and has an important role in clinical trials when other safety biomarkers for early toxicities are not available.

Measuring the progression of foreign-body reaction to silicone implants using in vivo MR microscopy

We used in vivo magnetic resonance (MR) microscopy to follow the growth of fibrous capsule as a foreign body reaction to silicone implants in rats. Anesthetized rats were imaged 1, 7, 14, and 28 days after silicone-coated MR imaging coils were sutured to their neck muscles. On the twenty-eighth day, rats were sacrificed and coils and adjacent tissues were removed en bloc and fixed in formalin, reimaged with MR, and sectioned for conventional histology. Three-dimensional (3-D) spin-echo [3DFT] acquisition gave in-plane resolution of 32 x 32 microns in vivo and 16 x 16 microns ex vivo. All MR images showed a diffuse band of elevated signal intensity between the silicone of the coil and adjacent tissue. The border of the hyperintense band was thin and not well defined at seven days post-implantation. From 7-28 days, the band showed relatively homogeneous signal intensity and its thickness increased 44% on the rectus muscle side and 78% on the subcutaneous side. The capsule thickness determined either by MR in vivo and ex vivo microscopy or conventional histology was not significantly different, and there was a significant correlation between thickness measurements among those methods. MR in vivo microscopy provides sufficient resolution and spatial information to serially evaluate the growth of the foreign body fibrous capsule over time, thus achieving greater accuracy and consistency in measurements.

Non invasive in vivo anatomical studies of the oscine brain by high resolution MRI microscopy

We describe in this paper an in vivo Magnetic Resonance Imaging (MRI) procedure that allows one to obtain three-dimensional high quality images of the entire brain of small passerine birds such as the canary with a slice thickness of 58 micron and an image resolution of 78 microns. This imaging procedure was completed in 70 min on anaesthetised birds that later recovered uneventfully and could be reused for subsequent additional imaging. To illustrate the high resolution and anatomical detail that can be achieved, examples of coronal images through the entire hypothalamus are provided in the same sectioning plane as the previously published canary brain atlas. The data set can be used to create sections in any desired plane and the entire data set can be viewed from any point of view in a volume rendered image. This provides a useful tool in understanding the three-dimensional organisation of the brain. Similar procedures can also be applied on fixed brains and might allow an even better anatomical resolution of images because time constrains no longer limit the duration of image acquisition. The non-invasive MRI technique enables to study neuroanatomical features with a high resolution and without killing the animal subjects so that measures can be obtained in a same individual both before and after an experimental treatment.

Magnetic resonance microscopy and histopathology: comparative approach of bromobenzene-induced hepatotoxicity in the rat

The development of magnetic resonance (MR) microscopy has provided new approaches to histology and histopathology. Recent work has shown the promise of increased sensitivity in animal models of chemically induced hepatotoxicity. However, the field is so new that there is little experience to relate changes seen in MR micrographs to the more traditional optical images stained with hematoxylin and eosin. This work compares the sensitivity and reproducibility of MR microscopy with conventional histopathology in detecting bromobenzene-induced hepatotoxicity in the rat. A time-course study was undertaken to provide a range of histopathologies. Specimens were studied at 24, 48, 72, and 96 hours after exposure to 10% of the median lethal dose of bromobenzene. Using 4 animals per group (a total of 32 rats) added statistical significance to the study and defined a range of interanimal variability over 96 hours. This work shows that MR microscopy, besides being nondestructive and three-dimensional, is at least as sensitive as conventional hematoxylin-eosin staining in detecting bromobenzene-induced centrilobular lesions and recovery of the hepatocellular architecture in the rat. This study further suggests that, as we begin to understand the underlying mechanisms of contrast in MR histology, MR may, in fact, supply even higher specificity than more traditional studies: variations were observed in MR images of treated livers at a given time point that could be not be differentiated based on the grading of necrosis and inflammation on hematoxylin-eosin-stained sections.

Magnetic resonance microscopy--a new tool for the toxicologic pathologist

Parallel to its many applications in medical imaging, magnetic resonance (MR) microscopy is a potentially powerful tool in toxicologic pathology. Because of the intrinsic qualities of MR microscopy (noninvasiveness, 3-dimensionality, and slicing in any chosen plane), the scientist has a new means by which to investigate different types of lesions based on differential contrast. By choosing appropriate proton stains to probe the state of the water in tissues, organ structure and vasculature can be seen and progressive lesion development can be followed in a given animal. This paper discusses toxicologic pathology applications for MR microscopy and compares MR microscopy with conventional histopathology using a time-course study of bromobenzene-induced hepatotoxicity in rats. Hematoxylin and eosin (H&E)-stained histological sections are compared with MR microscopy images from fixed tissue blocks to demonstrate one of the applications of MR microscopy to toxicologic pathology. The results indicate that MR microscopy is as sensitive as conventional H&E staining in detecting bromobenzene-induced hepatic lesions.