Assessment of Cardiac Function and Myocardial Morphology Using Small Animal Look-locker Inversion Recovery (SALLI) MRI in Rats

Summary

Contrast enhanced cardiac magnetic resonance (CMR) imaging allows comprehensive in vivo assessment of the heart in small animal models of cardiovascular disease. Here we detail the procedures to perform CMR imaging, reconstruction and analysis using Small Animal Lock-Locker Inversion Recovery (SALLI) in rats.

Abstract

Small animal magnetic resonance imaging is an important tool to study cardiac function and changes in myocardial tissue. The high heart rates of small animals (200 to 600 beats/min) have previously limited the role of CMR imaging. Small animal Look-Locker inversion recovery (SALLI) is a T1 mapping sequence for small animals to overcome this problem ¹. T1 maps provide quantitative information about tissue alterations and contrast agent kinetics. It is also possible to detect diffuse myocardial processes such as interstitial fibrosis or edema ^1-6. Furthermore, from a single set of image data, it is possible to examine heart function and myocardial scarring by generating cine and inversion recovery-prepared late gadolinium enhancement-type MR images ¹.

The presented video shows step-by-step the procedures to perform small animal CMR imaging. Here it is presented with a healthy Sprague-Dawley rat, however naturally it can be extended to different cardiac small animal models.

Introduction

Myocarditis is a major cause of acute heart failure, sudden death, and chronic dilated cardiomyopathy ⁷. CMR has been established as the gold standard technique for measurement of function and for in vivo tissue analysis. Novel imaging techniques and improvements in imaging could not only improve the diagnosis of myocarditis, but also aid the study of the pathophysiology and speed identification of therapeutic targets ^8-10. Small animal imaging is an important tool for the study of cardiovascular diseases. Techniques routinely used in clinical CMR, such as late gadolinium enhancement (LGE) cannot easily be transferred to small a....

Protocol

1. Preparation

1.1. Anesthesia of the rats

1. Place the rat into a chamber prefilled with isoflurane (depending on the size of the chamber about 3 minutes of 5%) to anesthetize the rat.
2. Once anesthetized, remove the rat and weigh it.
3. Place the nose of the rat into the anesthesia mask (isoflurane 2-3% in oxygen 1 L/min) to maintain anesthesia. During anesthesia with isoflurane, the heart rates of rats decrease to 300-340 bpm (380-420 bpm in mice).

1.2. Insert a tail vein cannula

1. Wash the tail of the rat with warm water (38 °C) and soap to allow the blood vessels to b....

Results

Here we demonstrate the findings from a healthy Sprague Dawley Rat. With a well-prepared animal setup we described before, it is possible to get a stable ECG signal. Similar to human cardiac MRI protocols, we start with a survey to locate the heart. If the position of the rat in the coil is correct, we continue with a two-chamber view and a four-chamber view to detect the geometry for the SALLI stack.

The SALLI technique produces three types of images acquired at the same time. These are, firs.......

Discussion

Here we present a method to generate multi-modality (cine MR, inversion-recovery and T1 maps) MR images in small animals. Small animal research plays an increasingly important role in cardiovascular disease research, and CMR is a powerful tool allowing us to study the function, structure and tissue composition of the myocardium. However, small animal CMR has a number of unique challenges owing to the high heart rates and small heart size. Improved methods of imaging, including more time efficient methods will play a furt.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Adhesive Tape (Silkafix)	Lohmann und Rauscher	34327
Gadopentetat-Dimeglumin (Magnevist)	Bayer	G-00012163	2mmol/Kg
Introcan Safety-W (G24)	B. Braun	4254503-01
Red Dot, Neonatal Monitoring Electrode with Pre-Attached Lead Wire	3M	2269T
Skin glue (Histoacryl)	B. Braun	1050052
Scales (Typ 440)	Kern	95088
Skin desinfection (Softasept N)	B. Braun Petzold	360250
Thermometer	LumaSense Technologies	Luxtron 812