Hunter, George Joseph Stephen; (2000) Digital radiology: A critical appraisal of cardiovascular subtraction angiography and measurement of blood flow. Doctoral thesis (M.D), UCL (University College London).

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Abstract

Throughout the 1970's, the integration of computers with radiological instruments was used to improve the ability of these instruments to visualize cardiovascular anatomy. Prototype machines that relied on computer technology came to fruition as usable commercial units circa 1982. For many years prior to this commercial availability, however, the measurement of absolute arterial blood flow had been possible with the aid of computer-assisted cine film and videodensitometric time-of-flight methods. The advent of digital subtraction angiography (DSA), as computerized fluoroscopy came to be known, allowed the feasibility of routine applications of videodensitometry to be reevaluated for the case of a DSA image series used as the source of both timing and spatial information. Anatomical imaging of some arterial structures is usually adequate following intravenous injection and of highest quality after the direct arterial injection of contrast material. Simultaneously with anatomical data, timing information can be extracted from the known time of image exposure and its acquisition. This allows functional or physiological imaging to be coupled with anatomical data. In this thesis, two principle applications of DSA are discussed, i) absolute volume blood flow and ii) relative blood flow and organ perfusion. Fourier transform methods are described for the measurement of time-of-flight and compared with existing curve fitting algorithms. The methods are analysed by using statistical modelling techniques (Monte-Carlo theory), and then validated in an animal model by using calibrated electromagnetic flow probes as the Gold Standard of volume blood flow. Clinical applicability of this technique is described and discussed in the context of relative organ perfusion and contrasted with methods of absolute flow estimation. The principal conclusion, supported by the animal validation, is that the Fourier method is more accurate than existing techniques in the presence of noisy data. Nevertheless, the much simpler relative flow techniques have a useful role in routine clinical practice, as exemplified by the parametric assessment of myocardial perfusion reserve.

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