W. Vennart

Magnetic resonance imaging techniques demonstrate soft tissue damage in the diabetic foot.

Aims Our objective was to assess the qualitative soft tissue changes which occur in the diabetic neuropathic foot, which may predispose to ulceration, using a specific magnetic resonance imaging (MRI) contrast sequence, magnetization transfer (MT) which produces contrast based on exchange between water bound to macromolecules (e.g. collagen) and free water (e.g. extracellular fluid).

Magnetic resonance imaging of rheumatoid arthritis in metacarpophalangeal joints.

Abstract  Objective. To report the development of high-resolution targeted magnetic-resonance imaging (MRI) techniques (not using injections of contrast media) to investigate and monitor rheumatoid arthritis (RA) in the metacarpophalangeal (MCP) joints. Design and patients. A total of 25 RA patients (age range 30–68 years) with varying degrees of disease severity ranging from early onset through active disease to the burnt-out stage, were imaged. (One patient subsequently underwent surgery and histological data was obtained.) A series of 10 control subjects were also studied – two for each 10-year age range. All the RA subjects were assessed for disease activity using standard clinical criteria and radiography as part of normal procedures. MRI was carried out using a targeted system and novel radiofrequency coil. Images of the MCP were performed at very high resolution with 1.5 mm slice thickness and in-plane resolution 130 µm. Standard gradient-echo (GE) sequences were used for anatomical imaging, multiple-echo GE sequences used to produce effective spin-spin relaxation time (T2*) maps and optimised binomial-pulse presaturation used in conjunction with a GE sequence to generate magnetization-transfer (MT) ratio maps. Results. High-quality high-resolution images of the MCP joints were obtained which highlighted normal anatomy and key features characterising the disease state (e.g. pannus, bone erosions, vascularity). Accurate measurements of T2* and MT with variations of ±4% and ±2% respectively were achieved. In active disease, variations in T2* and MT could be determined throughout areas of pannus, clearly demonstrating the heterogeneity of this erosive tissue. Pannus in MCP joints with active destruction was found to have high values of T2* varying from 25 ms to 40 ms with pockets up to 100 ms, whereas pannus present in chronic destruction, or burnt-out disease, had T2* values ranging from 21 to 29 ms. MT-active tissue was uniformly distributed in burnt-out disease, which was confirmed histologically in one case, compared with a more heterogeneous distribution in active disease. Conclusion. The MRI sequences and targeted system developed allow high-resolution studies of RA disease progression and activity. The data confirm the variable pattern of the disease and, in particular, heterogeneity of pannus.

High-resolution magnetic resonance imaging of the interphalangeal joints of the hand

High-resolution magnetic resonance imaging (MRI) of the interphalangeal joints of the fingers is being employed to study arthritis. To facilitate this research, a clear understanding of the structures visualisable by MRI is necessary. A gradient echo (GE) sequence was developed that produced good contrast between cartilage and other joint structures. These detailed images, with an in-plane resolution of 200 × 100 μm, enable resolution of three cartilage zones which can be interpreted as a superficial layer at the cartilage/cartilage interface, an intermediate layer and calcified cartilage in contact with bone; these correlate well with known anatomy. Further analysis of the images indicates that although a chemical shift artifact causes changes in the images at the field strength used (0.5 T), it does not cause enough distortion to necessitate suppression of the effect. Furthermore, the only detectable susceptibility artifact at these low field strengths was a loss of signal in bone trabeculae at the bone/cartilage interface. There is clearly potential in the study of the articular structures, in particular cartilage, in detail, using high-resolution MRI.High-resolution magnetic resonance imaging (MRI) of the interphalangeal joints of the fingers is being employed to study arthritis. To facilitate this research, a clear understanding of the structures visualisable by MRI is necessary. A gradient echo (GE) sequence was developed that produced good contrast between cartilage and other joint structures. These detailed images, with an in-plane resolution of 200 × 100 μm, enable resolution of three cartilage zones which can be interpreted as a superficial layer at the cartilage/cartilage interface, an intermediate layer and calcified cartilage in contact with bone; these correlate well with known anatomy. Further analysis of the images indicates that although a chemical shift artifact causes changes in the images at the field strength used (0.5 T), it does not cause enough distortion to necessitate suppression of the effect. Furthermore, the only detectable susceptibility artifact at these low field strengths was a loss of signal in bone trabeculae at the bone/cartilage interface. There is clearly potential in the study of the articular structures, in particular cartilage, in detail, using high-resolution MRI.

Magnetic resonance imaging reveals micro-haemorrhage in the feet of diabetic patients with a history of ulceration

Soft tissue haemorrhage in the foot is a possible precursor of ulceration in patients with diabetic peripheral neuropathy. High resolution ‘targetted’ magnetic resonance imaging was used to scan the forefoot. Neuropathic patients with and without previous ulceration were matched for degree of neuropathy, mean vibration perception threshold 33.5 ± 4.2 V (previous ulcer) vs 31.0 ± 6.9 V (no ulcer), age, sex, and duration of diabetes against non‐neuropathic controls. There were nine patients in each category. Paramagnetic materials, e.g. iron compounds, cause a signal void (‘drop‐out’) on gradient‐echo images which disappear on spin‐echo images. Evidence of haemorrhage was seen in 6 patients with previous ulceration, and none in the other groups (p = 0.009, chi square test). Autologous injection of 20 μl of blood into the foot of a healthy volunteer produced similar images, a ‘drop‐out’ 1 cm across being visible on magnetic resonance scanning 3 days later. Peak vertical forefoot pressures were not significantly different in the neuropathic groups 0.67 ± 0.20 vs 0.60 ± 0.13 Pa but were lower in the non‐neuropathic group, 0.43 ± 0.11 Pa (p = 0.0004, Mann‐Whitney), and do not explain the appearance of these haemorrhages. Magnetic resonance imaging provides a sensitive way of detecting micro‐haemorrhage and its presence may predict an increased risk of foot ulceration.

A low-cost magnetic resonance imaging system

The design, construction and performance of a low-cost magnetic resonance imaging (MRI) system is described. The system uses a unique, PC-based, task-oriented multiprocessor design, resulting in a high-performance MRI system able to run most pulse sequences. This type of design could lead to a new generation of low-cost MRI systems with applications in research and teaching.

Automatic realignment of time-separated MR images by genetic algorithm.

A simple yet highly efficient artificial intelligence technique utilizing a genetic algorithm is used to register time-separated pairs of MRI data sets. To encourage others to try the approach, the algorithm is presented by way of a simple example to a 2-D data set; it is equally applicable to 3-D data. The technique is reliably found to reduce mismatch in images of the distal-interphalangeal joint from the order of several mm to just 200 microm (one pixel). The method and transformation are general and would be suitable for locating physical changes between any image data sets. We believe the technique to be of use in functional imaging, measurement of disease progression with time (e.g., degradation of cartilage in arthritic disease) and pre/post-surgical studies.

Water diffusion coefficient measurements in the finger by magnetic resonance imaging

Diffusion coefficients of water have been measured in the fingers of humans by magnetic resonance imaging. It was found that the measured diffusion coefficients increased with subject age in certain regions of the finger but that these regions differed between males and females. The observation of an increased diffusion coefficient with age appears to be inconsistent with a direct-hydration model and possible explanations are given using other models. It is conjectured that the measured diffusion coefficient of water increases with age as a result of structural changes to proteins.

Magnetic resonance imaging of peripheral vascular disease and muscle atrophy in diabetes

Knowledge of the state of tissue hydration in patients suffering from peripheral vascular disease and neuropathy as a result of diabetes is important in their treatment. Further, because magnetic resonance imaging (MRI) is uniquely able to generate information about soft tissues and their water content, it is ideal for studying disorders of this kind. The feet and hands, often affected in diabetes, are ideal for studying fundamental aspects of the disease state and the response of patients to treatment. In this preliminary study, two related areas are reported: the measurement of diffusion coefficients in the finger and the visualization of the distribution of edema and muscle atrophy in the feet of people suffering from diabetes. Diffusion coefficients of water have been measured in the normal finger as a baseline study for a current patient study. It was found that the measured diffusion coefficient increased with subject age; this is not consistent with a direct-hydration model and it is conjectured that this could be linked to structural changes in proteins. Linked to this study, we have also imaged the feet of patients suffering from diabetes. Magnetization transfer has clearly demonstrated changes in muscle tissue with atrophy caused by motor neuropathy—in general, the amount of tissue water is increased as muscle volume decreases. Further, it is evident that these changes can be related to changes in cross-linking of protein and collagen molecules as muscle fibers become thinned, thus relating these studies to the diffusion coefficient measurements. The studies of the feet have also revealed artifacts in the images, consistent with the deposition of ferrous material in tissues. It is surmised that this is caused by hemosiderin deposits at ulcer sites associated with progress of the disease. MRI could be a useful tool for monitoring the distribution of ulcers below the skin surface and provide a means of determining the response of patients to treatment.

MRI for arthritis research: current pitfalls and future prospects

Arthritis is intimately associated with the destruction of cartilage. High-resolution (100–200-μm)in vivo images of the finger joints have been obtained using a targeted magnetic resonance imaging (MRI) system. The study of asymptomatic subjects has enabled the normal anatomical zones of cartilage as visualised by MRI to be identified. In patients with advanced osteoarthritis features such as osteophytes and loss of cartilage are clearly demonstrated. An obvious question is whether MRI can be used to measure cartilage thickness and then whether this parameter can be utilized to quantify cartilage loss during the evolution of disease processes or response to therapy. However, there are a number of difficulties with this measurement which are discussed. It is possible that more valuable insights may be gained by careful choice of specific arthropathies to be studied—for example, acromegaly, which can lead to osteoarthritis—offers a way of observing subtle early changes that occur in the cartilage and subchondral bone.

Low-cost magnetic resonance imaging

AbstractOf the established medical imaging teclmiques magnetic resonance imaging (MRI) is the most sophisticated and one of the most expensive. The high capital cost of MRJ systems is due in part to the requirement of a large magnet and also the supporting computer system. For the last three years Exeter has been developing a low-cost MRI system to image wrists and hands for the study of arthritis. The Exeter system utilizes the latest generation of specialist microprocessors to undertake image reconstruction at a fraction of the cost of a commercial system. This paper describes a practical realization of a low-cost microprocessor based MRI image reconstruction system that demonstrates the elegance of this imaging modality and its potential for medical research and diagnosis.