Clinical application of hybrid subtraction digital angiography: preliminary results

A theoretical comparison of x-ray angiographic image quality using energy-dependent and conventional subtraction methods

PURPOSE

X-ray digital subtraction angiography (DSA) is widely used for vascular imaging. However, the need to subtract a mask image can result in motion artifacts and compromised image quality. The current interest in energy-resolving photon-counting (EPC) detectors offers the promise of eliminating motion artifacts and other advanced applications using a single exposure. The authors describe a method of assessing the iodine signal-to-noise ratio (SNR) that may be achieved with energy-resolved angiography (ERA) to enable a direct comparison with other approaches including DSA and dual-energy angiography for the same patient exposure.

METHODS

A linearized noise-propagation approach, combined with linear expressions of dual-energy and energy-resolved imaging, is used to describe the iodine SNR. The results were validated by a Monte Carlo calculation for all three approaches and compared visually for dual-energy and DSA imaging using a simple angiographic phantom with a CsI-based flat-panel detector.

RESULTS

The linearized SNR calculations show excellent agreement with Monte Carlo results. While dual-energy methods require an increased tube heat load of 2× to 4× compared to DSA, and photon-counting detectors are not yet ready for angiographic imaging, the available iodine SNR for both methods as tested is within 10% of that of conventional DSA for the same patient exposure over a wide range of patient thicknesses and iodine concentrations.

CONCLUSIONS

While the energy-based methods are not necessarily optimized and further improvements are likely, the linearized noise-propagation analysis provides the theoretical framework of a level playing field for optimization studies and comparison with conventional DSA. It is concluded that both dual-energy and photon-counting approaches have the potential to provide similar angiographic image quality to DSA.

Retrospective motion correction in digital subtraction angiography: a review

Digital subtraction angiography (DSA) is a well-established modality for the visualization of blood vessels in the human body. A serious disadvantage of this technique, inherent to the subtraction operation, is its sensitivity to patient motion. The resulting artifacts frequently reduce the diagnostic value of the images. Over the past two decades, many solutions to this problem have been put forward. In this paper, we give an overview of the possible types of motion artifacts and the techniques that have been proposed to avoid them. The main purpose of this paper is to provide a detailed review and discussion of retrospective motion correction techniques that have been described in the literature, to summarize the conclusions that can be drawn from these studies, and to provide suggestions for future research.

Left ventricular dual-energy digital subtraction angiography: a motion immune digital subtraction technique

Digital subtraction angiography (DSA) allows quantitative analysis of ventricular function via densitometric and parametric imaging techniques. However, DSA is limited by the artifacts in temporal subtraction images that result from patient and cardiac motion. Dual-energy subtraction imaging is insensitive to motion. This study evaluated the initial application of dual-energy subtraction in cardiac patients. The image quality of dual-energy subtraction left ventriculograms obtained from a pulmonary artery injection of contrast was assessed in 13 patients, ranging in weight from 54 to 100 kg. The dual-energy images were compared with left ventricular images obtained using standard left ventricular injection cine angiography. End-systolic and end-diastolic ventricular volumes calculated from the cine (C) and dual-energy (DE) images using the Area-Length method were compared. The resulting regression line was DE = 0.98 C+ 7.0 ml, and the r value was 0.987. Dual-energy subtraction provided good left ventricular visualization, free from misregistration artifacts, even during patient motion.

High resolution DSA: experimental and clinical evaluation

The DSA system has been upgraded for capabilities of slow scan video technique and progressive T.V. read-out of 1024 X 1024 matrix with 10 bits of depth. A square wave test pattern made of lead bar demonstrated moderate improvement in spatial resolution, but imaging of a Burger-Rose phantom revealed no significant increase in contrast resolution. Clinical study of various angiograms with intraarterial injections showed that there was slight improvement in the visibility of the vessels, especially small arterial branches, while there was no increase in visibility of the veins. There were no cases in which diagnoses were altered by application of high resolution DSA. With future improvements of the image intensifiers, DSA with 1024 X 1024 matrix may reveal its potential advantage, especially when coupled to larger image intensifiers such as 12 or 14 in.

Hybrid digital subtraction angiography: initial clinical experience

Hybrid digital subtraction angiography was performed after modification of a DSA system. Alternate high voltage (110-120 kV) and low voltage (65-70 kV) were obtained within short time intervals of 60-70 ms with a high voltage switching generator. Experimental phantom studies revealed the exposure dose per single image of hybrid subtraction was approximately 30% of that of conventional DSA. The SNR of hybrid subtraction was improved by increasing the exposure dose and application of postprocessing programs. Clinical application of intraarterial and intravenous DSA revealed that soft tissue artifacts were removed surprisingly well, but image quality decreased because of lowered SNR. Frame integration and matched filtering improved image quality of hybrid subtraction.