PET, SPECT, CT, and MRI in Mouse Cardiac Phenotyping: An Overview

Recent Advances in Cardiovascular Diseases Research Using Animal Models and PET Radioisotope Tracers

Cardiovascular diseases (CVD) is a collective term describing a range of conditions that affect the heart and blood vessels. Due to the varied nature of the disorders, distinguishing between their causes and monitoring their progress is crucial for finding an effective treatment. Molecular imaging enables non-invasive visualisation and quantification of biological pathways, even at the molecular and subcellular levels, what is essential for understanding the causes and development of CVD. Positron emission tomography imaging is so far recognized as the best method for in vivo studies of the CVD related phenomena. The imaging is based on the use of radioisotope-labelled markers, which have been successfully used in both pre-clinical research and clinical studies. Current research on CVD with the use of such radioconjugates constantly increases our knowledge and understanding of the causes, and brings us closer to effective monitoring and treatment. This review outlines recent advances in the use of the so-far available radioisotope markers in the research on cardiovascular diseases in rodent models, points out the problems and provides a perspective for future applications of PET imaging in CVD studies.

Accuracy of cardiac functional parameters measured from gated radionuclide myocardial perfusion imaging in mice

BACKGROUND

Quantitative cardiac contractile function assessment is the primary indicator of disease progression and therapeutic efficacy in small animals. Operator dependency is a major challenge with commonly used echocardiography. Simultaneous assessment of cardiac perfusion and function in nuclear scans would reduce burden on the animal and facilitate longitudinal studies. We evaluated the accuracy of contractile function measurements obtained from electrocardiogram-gated nuclear perfusion imaging compared with anatomic imaging.

METHODS AND RESULTS

In healthy C57Bl/6N mice (n = 11), 99mTc-sestamibi SPECT and 13N-ammonia PET underestimated left ventricular volumes (23 to 28%, P = 0.02) compared to matched anatomic images, though ejection fraction (LVEF) was comparable (%, SPECT: 73 ± 8 vs CMR: 72 ± 6, P = 0.1). At 1 week after myocardial infarction (n = 13), LV volumes were significantly lower in perfusion images compared to CMR and contrast CT (P = 0.003), and LVEF was modestly overestimated (%, SPECT: 37 ± 8, vs CMR: 27 ± 7, P = 0.003). Nuclear images exhibited good intra- and inter-reader agreement. Perfusion SPECT accurately calculated infarct size compared to histology (r = 0.95, P < 0.001).

CONCLUSIONS

Cardiac function can be calculated by gated nuclear perfusion imaging in healthy mice. After infarction, perfusion imaging overestimates LVEF, which should be considered for comparison to other modalities. Combined functional and infarct size analysis may optimize imaging protocols and reduce anaesthesia duration for longitudinal studies.

Fundamentals of Microscopy

The light (or optical) microscope is the icon of science. The aphorism "seeing is believing" is often quoted in scientific papers involving microscopy. Unlike many scientific instruments, the light microscope will deliver an image however badly it is set up. Fluorescence microscopy is a widely used research tool across all disciplines of biological and biomedical science. Most universities and research institutions have microscopes, including confocal microscopes. This introductory paper in a series detailing advanced light microscopy techniques explains the foundations of both electron and light microscopy for biologists and life scientists working with the mouse. An explanation is given of how an image is formed. A description is given of how to set up a light microscope, whether it be a brightfield light microscope on the laboratory bench, a widefield fluorescence microscope, or a confocal microscope. These explanations are accompanied by operational protocols. A full explanation on how to set up and adjust a microscope according to the principles of Köhler illumination is given. The importance of Nyquist sampling is discussed. Guidelines are given on how to choose the best microscope to image the particular sample or slide preparation that you are working with. These are the basic principles of microscopy that a researcher must have an understanding of when operating core bioimaging facility instruments, in order to collect high-quality images. © 2020 The Authors. Basic Protocol 1: Setting up Köhler illumination for a brightfield microscope Basic Protocol 2: Aligning the fluorescence bulb and setting up Köhler illumination for a widefield fluorescence microscope Basic Protocol 3: Generic protocol for operating a confocal microscope.

Evaluating Systolic and Diastolic Cardiac Function in Rodents Using Microscopic Computed Tomography

BACKGROUND

The use of microscopic computed tomography to assess the key functional parameters of systolic emptying or diastolic filling in small animals has not been previously reported. The aim of the study was to test whether microscopic computed tomography can assess the dynamics of both left ventricle and right ventricle (RV) diastolic filling and systolic emptying in an experimental model of pulmonary arterial hypertension Methods and Results: The Wistar-Kyoto rats were injected subcutaneously with the VEGF (vascular endothelial growth factor)-receptor inhibitor SU5416 (20 mg/kg body weight) and were then exposed to chronic hypoxia (10% oxygen) for 21 days (SU5416-hypoxia) followed by normoxia for an additional 2 weeks. Thereafter, multiphase cine cardiac images were acquired using a microscopic computed tomography scanner in conjunction with a blood-pool iodinated contrast agent. Examination of the 3-dimensional images of SU5416-hypoxia rats confirmed the presence of severe pulmonary arterial hypertension. Functional parameters that describe the dynamics of ventricular systolic ejection and diastolic filling were calculated. RV peak ejection rate was significantly decreased ( P<0.03) in SU5416-hypoxia rats compared with controls. RV peak filling rate had a significant decrease compared with controls ( P<0.03), particularly in the early phase of diastole ( P<0.03). This was accompanied by increased time to peak filling rate ( P<0.03) and total filling time ( P<0.06). Spearman analysis between microscopic computed tomography RV diastolic indices and invasively derived RV end-diastolic pressure indicated excellent correlation.

CONCLUSIONS

We developed a method that allows rapid and accurate assessment of cardiac functional indices and that paves the way for more extensive preclinical cardiovascular research.