Sheffield Hyperpolarised Imaging of Metabolism and MR Engineering Research

SHIMMER

9.4T Imaging

The combination of high magnetic field and gradient strength allows objects to be scanner at high resolution, 10-20 μm. Figure 1 shows an excised P22 tumour that had been injected with USPIO nanoparticles. Using this data we developed a method to calculate the apparent vasculature to tissue volume.

Figure1

Left Panel: Single plane from a high resolution 3D data set acquired from a formalin fixed, excised P22 sarcoma following USPIO injection 15 minutes prior to sacrifice.

Right panel: A zoomed region from one of the slices showing accumulation of USPIO in the outer rim and central region of the sarcoma as well as small micro-vessels with 25 Μμ in-plane resolution and 200 Μμ slice thickness.

In conventional MR imaging cortical bone and tendons with high collagen content are generally shown as areas of signal void in the image, irrespective of image weighting.

Recently there has been increasing interest in the use of Ultra-short1 and Zero TE2,3 (UTE and ZTE) sequences which can provide unprecedented high resolution imaging of these bone structures in the presence of severe susceptibility artefact by minimising the time available for T2* signal dephasing.

By shortening the TE it is possible to produce positive contrast from cortical bone if necessary.

By combing very strong gradients together with custom sized close fitting radiofrequency coils allows acquisition of images with spatial resolution of 10’s of microns, see figure 2.

Figure 2

Figure 3

Obesity is a serious and growing problem worldwide and has many co-morbidities that lead to further health problems, e.g. type 2 diabetes. It has been proposed that there are many genetic components to an individual’s risk of developing type 2 diabetes. Tribbles pseudokinase 3 (TRIB3) is one of three tribbles kinase like proteins found in mammals. Studies have shown an increase of the TRIB3 protein in diabetic insulin resistant mice, and overexpression in other metabolic disorders.

Additionally TRIB3 has been associated with loss of pancreatic β cells resulting in a decrease in insulin secretion. Pilot studies conducted by us in collaboration with colleagues in Cardiovascular science showed that male mice with the gene for TRIB3 knocked out had an increased body mass over wild type mice. As insulin induces adipogenesis, if TRIB3 acts as an inhibitor of insulin, then removing the gene for TRIB3 may result in an increase in body fat. In collaboration with Endre Kiss-Toth we use MRI to compare the fat volume, body volume and fat to body volume ratio in sacrificed male and female TRIB3 knock out and C57 mice, see figure 3.

In a cross departmental study with the Department of Materials Science and Engineering, we are using MRI to examine the formation of silk in live, domesticated, species of silkworm - Bombyx mori. Silk fibres are formed from a proteinaceous mixture, also referred to as silk dope. The process of silk spinning occurs in two large silk glands; see Figure 4. The posterior section of the gland is responsible for secreting the protein components (Fibroins) that constitute the silk dope, which is then stored in the middle section before being spun through a specially tapered silk duct which initiates silk fibre formation via flow induced protein denaturation before exiting the body through the animal’s spinneret. Previous rheological studies on excised silk dope from the silk gland have shown that silk is stored as a viscous gel before undergoing various chemical and mechanical changes during spinning1. In this study we determine the T1 and T2 per voxel in contiguous slices of live silkworms as an indicator of the rheological properties of the silk dope as it passes through the gland and duct.

Figure 4