Intravascular ultrasound and magnetic resonance imaging of the pulmonary arteries in pulmonary hypertension
McLeod, Karen A.
Two relatively new techniques by which the pulmonary arteries can be imaged in life are intravascular ultrasound and magnetic resonance imaging. The main aim of this thesis is to describe the changes which are detectable on intravascular ultrasound and magnetic resonance imaging in patients with pulmonary hypertension and to determine whether these imaging modalities could be of use for the clinical assessment of the condition.Intravascular ultrasound was performed in 10 young adults with Eisenmenger's Syndrome and 4 infants with pulmonary hypertension secondary to a left to right shunt. Vasodilator studies were performed in 5 of the patients with Eisenmenger's. The vessel wall appeared as a single echogenic layer in all patients, making it difficult to define or measure medial thickness with certainty. Morphological changes of intimal hypertrophy and atherosclerosis were evident in patients with Eisenmenger's whereas in the infants the intima appeared thin and smooth, typical of normal artery. The technique gave excellent definition of the vessel lumen allowing continuous measurement of changes in luminal dimensions in response to vasodilators.MRI of the pulmonary arteries was performed in 11 patients with Eisenmenger's and 6 normal controls. In patients with pulmonary hypertension the pulmonary arteries were found to be dilated with reduced distensibility 4 when compared with normals. Calculations of Qp:Qs by MRI in patients with systemic to pulmonary shunts and pulmonary hypertension did not correlate well with values from cardiac catheterisation in all patients.As intravascular and magnetic resonance imaging are confined to the elastic pulmonary arteries, quantitative morphological studies were peformed on 24 post mortem specimens of lungs from patients who had died with pulmonary hypertension to determine whether there was any correlation between changes in the elastic pulmonary arteries and severity of pulmonary vascular disease. When compared with normals there was medial thickening in those with pulmonary hypertension but this was of an insufficient degree to be detectable by current ultrasound catheters. There was no correlation between degree of medial thickening in the elastic pulmonary arteries and severity of pulmonary vascular disease but intimal thickening and atherosclerosis were evident in those with more advanced disease.In conclusion, magnetic resonance imaging was found to have limited role in the assesssment of pulmonary hypertension but with new technical developments could become a non-invasive method of studying pulmonary hypertension in the future. The morphological changes detectable by intravascular ultrasound tend to be in severe disease only but the technique provides a unique method of studying pulmonary vascular reactivity in life.