The development of functional imaging of the diabetic forefoot using a targetted magnetic resonance system.
The importance of soft tissue structures in the pathogenesis of diabetic complications in
the hand and particularly the forefoot due to nerve damage or neuropathy has long been
overlooked. This is partly due to the inability of most clinical techniques to examine
tissue structures in vivo. Magnetic Resonance Imaging (MRI) provides a unique
opportunity to study these tissues in detail. Through the use of a specially designed
"targetted" radiofrequency coil, high-resolution imaging of the forefoot anatomy has
been achieved. In addition to anatomical imaging, MRI has been used to give functional
information about water dynamics in various tissue types, e. g. the fat pad and the
muscles in the foot. The potential of this type of information to provide an insight into
the severity and progression of diabetes has been investigated during this research work.
In detail two patient groups with and without symptoms of neuropathy have been
investigated. Deterioration of foot joints with a collapsed arch and intrinsic muscle
wasting due to nerve damage were observed but more importantly several as yet
unknown and unobserved phenomenon were also demonstrated.
(i) At sites of maximum pressure resulting from neuropathic changes evidence of
microhemorrhaging (or localised hemosiderin deposits) was observed through signal
voids when using a gradient echo sequence. It is postulated that the occurrence of these
voids is due to the paramagnetic iron core of the hemosiderin aggregate and therefore
the signal from tissue in its proximity may be recovered with a spin echo sequence.
(ii) The use of a Magnetisation Transfer (MT) sequence to provide functional
information revealed a distinct change in MT activity deep within the fat pad of the foot
at sites of maximum pressure. This is in contrast to the normal fat pad core which is MT
inactive since its hydrophobic nature prevents the adsorption of free water. The fat pads
of patients suffering from neuropathy showed various degrees of MT activity which hasbeen taken to indicate the presence of fibrotic material as a replacement for fat. This is
consistent with current theories of the formation of neuropathic ulcers. The fibrotic
tissue is likely to be the result of repetitive trauma to fat tissues leading to fibrosis where
the condition of diabetes serves to catalyse its production via glycation and cross-linking
of collagen. Histopathological examination of the fat pad tissues of similar patients,
confirmed the presence of fibrosis. This is the first time that such a change in plantar fat
pad tissue has been demonstrated in vivo. Further it was possible to correlate the extent
of MT activity with disease severity.
(iii) In an additional study of Limited Joint Mobility in the metacarpophalangeal (MCP)
joints of the hand it was found that the cross-sectional area of the joint capsule reduced
linearly with age for patients and controls and that there was no significant thickening
relative to controls as postulated from work by others using plain radiographs