Parametric imaging using digital subtraction angiography

Abstract

Digital subtraction angiography following an injection of iodinated contrast material can regularly produce good quality images. In addition to the conventional anatomical information, the timed sequence of digital images also contains useful temporal information which hitherto has been largely ignored. A simple method of image processing is described which utilises this timing information and presents it as a colour-coded set of functional images. Three parameters MAX, T-MAX and T-1/2 MAX are extracted from time-density curves, analogous to the time-activity curves of Nuclear Medicine, on a pixel-by-pixel basis. These parameters are used as a measure of overall organ perfusion, blood transit time between different vascular compartments, and as an indication of the initial delivery of contrast material to an organ. They have found use in the analysis of myocardial perfusion, before and after pharmacological intervention, and in the examination of the cerebral and renal circulations. The potential advantages of this technique derive from its superior spatial, temporal and contrast resolution.

Perfusion Angiography in Acute Ischemic Stroke

“…In contrast with MR and CT perfusion imaging that have been studied through clinical trials (e.g., DEFUSE [ 7 ]), the value of parametric imaging from DSA has been largely underappreciated. While the idea of extracting perfusion parameters from DSA has been introduced since the 1980s in sporadic studies for CBF [ 8 ], MTT [ 9 ], TTP [ 10 ], and T max [ 10 , 11 ], it has not yet received the attention deserved by the acute stroke community. This overall lack in interest may be caused by the difficulty of real-time implementation of those algorithms on angiographic units, challenges due to the nature of the images (artifacts, vessel overlap), or perhaps failure to realize its full potential for quantitative decision support.…”

A review of the display of combined images

“…In many areas of imaging, the computer system is the basis for the acquisition, image reconstruction, processing and display of data from techniques such as X-ray computed tomography (XRCT) [1], single-photon-emission computed tomography (SPECT) [2,3], positron-emission computed tomography (PECT) [4,5], magnetic resonance imaging (MRI) [6,7] and digital fluorography [8]. In other imaging techniques such as thermography, ultrasound, transillumination [9] and conventional radiography, the data may be converted into digital form for the purposes of archiving, processing and display.…”

Color-Coded Digital Subtraction Angiography: The End of a Monochromatic Era?

“…11, 12 Hunter et al, in 1986, 12 presented an interesting postprocessing technique to extract physiologic information by using time-attenuation curves. They were able to prove that such an approach can add useful information about renal, cardiac, and cerebral perfusion.…”

“…Probably, because the use of color in medical imaging in general was still in its early stages and the era of computed digital imaging had just begun. Possibly also, because Hunter et al 12 were simply ahead of their time, a period in which most radiologists thought conventional angiography would soon disappear from the radiologic imaging armamentarium.…”

“…It has become increasingly easy in medical imaging to create powerful images that may trick the observer into taking them for reality. 13 The use of time-attenuation methods, as initially suggested by Hunter et al, 12 may be less accurate because they produce only an estimate of the average velocity. 13 Reproducibility of color-coding could be another issue requiring calibration techniques to ensure accuracy for pre-and postprocedure comparisons or for longitudinal studies.…”