Recent advances: Diagnostic radiology

British Medical Journal, July 17, 1999 by Jane Hawnaur

Radiology has participated in the recent trend towards computerised management in the health service and has responded to the demand for cost efficient and rapid communication between departments of radiology and their users. Digital image acquisition has become the standard for modern equipment used in angiography, ultrasonography, computed tomography, magnetic resonance imaging, and radionuclide radiology, but most radiological images are still recorded, interpreted, and stored on x ray film. With the increasing availability of more efficient and affordable storage phosphor systems, the simple radiograph looks set to become digital and the "filmless" radiology department will be a reality. In this review I discuss this topic and other aspects of radiology in which technological advances have had an impact on clinical practice.

Method

Although tremendous progress has been made in interventional radiology in recent years, I have confined this review to advances in diagnostic imaging that have resulted from recent technical innovations. Some applications have evolved only recently from research techniques and may not yet have undergone stringent clinical evaluation. This review comprises a personal selection of recent reports from mainstream radiology journals and the results of Medline searches which examine the highlighted topics in more depth.

Digital radiology departments and teleradiology

x Ray film is exposed by light photons emitted by intensifying screens sensitive to radiation transmitted through the patient. Storage phosphor technology uses photostimulable phosphor screens to directly convert x ray energy into digital signals.[1] The increased dynamic range and image contrast of digital radiography compared with conventional x ray film-screen combinations and the facility to manipulate signal intensity after image capture reduce the number of repeat exposures, thereby increasing radiographic efficiency and reducing the radiation dose received by patients. As long as all equipment conforms to the Digital Image Communication in Medicine-3 standard, digital images can be made available immediately on a local network--for example, on the radiologist's workstation for reporting or for transmission to a ward based computer for review. Many radiology departments aspire to these picture archiving and communication systems because they enjoy greater efficiencies of image production, radiological report generation, and data storage, retrieval, and transmission, but the initial capital costs are high.[2-4] Thus, replacing old management systems is often done gradually, and in the United Kingdom, the evaluation of complete picture archiving and communication systems has been limited to pilot sites.[5]

In teleradiology digital images are transmitted over a distance by a communications network. For many typical digital radiological studies--for example, computed tomography of the thorax--the electronic file is very large, and only with the availability of compression algorithms and higher bandwidths for transmission has full implementation of teleradiology become feasible.[6] Studies indicate that the process of image compression, transmission, decompression, and display on relatively low resolution monitors does not reduce the ability of radiologists to interpret the images.[7] The potential benefits of this technology include financial savings on x ray film and storage costs, rapid transmission of images between departments or to specialist centres for an expert opinion, and "on call" interpretation of some emergency examinations from a computer terminal in the radiologist's home. Paperless radiology departments may be the next step; commercially available voice activated reporting systems work well in clinical practice and reduce appreciably the time taken to generate a printed report.[8]

Computed tomography

The introduction of slip ring technology into the design of computed tomography scanners revitalised a mature technique in which progress had stalled in the 1980s. Current computed tomography scanners can acquire data in a continuous helical or spiral fashion, shortening acquisition time and reducing artefacts caused by patient movement."[9] Faster scanning increases the likelihood of a diagnostically useful scan in patients who have difficulty cooperating with the investigation and increases patient throughput. A choice of image processing techniques is available to display volumetric data obtained during a "breathhold" in ways appropriate to the clinical question (fig 1).[10] For example, "virtual" endoscopy using reconstructed computed tomographic data to simulate intraluminal views of hollow organs may be useful in patients who are unsuitable for invasive endoscopy.[11]

[Figure 1 ILLUSTRATION OMITTED]

The use of contrast enhanced spiral computed tomography to show pulmonary emboli is gaining clinical acceptance, as it offers a relatively non-invasive technique with better specificity than radionuclide lung scans.[12] Pulmonary embolism can be confirmed or excluded in patients with an indeterminate radionuclide study without having to perform pulmonary angiography, although the sensitivity of computed tomography for peripheral emboli is inferior. In other parts of the vascular system, contrast enhancement can be timed to show hepatic arterial and portal venous anatomy or the nephrographic and corticomedullary phases of renal enhancement, thereby increasing diagnostic accuracy.[13 14]