Major advances in radiology in recent years can be attributed to the change from analogue to digital imaging and to advances in electronics and computing.1

Digital imaging. Modalities such as ultrasound, computed tomography, magnetic resonance imaging and nuclear medicine are digital, but have been displayed in analogue format (ie, film) for easy manipulation with conventional radiographs. However, digital radiography units, digital screening units and scanning of conventional films (computed radiography) are now accepted technologies, with resolution similar to that of film/screen techniques. Digitisation itself is a critical advance, as it allows manipulation of the images.

Digital images can be transferred within a hospital's network as part of a picture-archiving and communication system (PACS), or examined from remote locations via telecommunication networks (teleradiology), which obviates the need to physically transport films to a reporting location and better enables distance radiology services for outlying communities.

Radiology still uses techniques similar to those discovered by Roentgen in 1895. Film is exposed, developed, coded and placed in packets, reported, and then stored for review. With PACS, a clinician (or many clinicians simultaneously) can review the images as soon as they have been processed, and consultation between physicians can take place without physical meetings. The PACS connects to the Radiology Information System (RIS) and the Hospital Information System (HIS), avoiding multiple entering of patient data and allowing planning for patient bookings. Future PAC systems will be able to track patient progress via the RIS and HIS and pre-emptively fetch images from the electronic archive to the appropriate clinical workstations for outpatient lists or operative lists.

Cross-sectional imaging. Advances in electronics and computing, combined with helical CT technology and the development of fast-gradient coils in MRI, has made possible rapid high-resolution scanning. The consequent reduction in motion and respiratory artefacts leads to:

• The ability to optimise the timing of intravenous contrast medium enhancement, which enables relatively non-invasive CT and MR angiography and multiphasic post-contrast scan acquisition, such as in liver imaging;

• The capability for volume-acquisition of data, leading to multiplanar reformatting from data acquired in a single plane, and three-dimensional reformatting for surgical planning or for endoluminal navigation (eg, "virtual endoscopy"); and

• Functional imaging, such as perfusion CT and MR imaging of the brain and MR spectroscopy.

Current multidetector-array CT scanners have four rows of detectors. Scanners with larger arrays will be released soon, enabling finer, morphologically detailed three-dimensional and even four-dimensional imaging (virtually real-time functional imaging).

MRI has diversified from its original musculoskeletal and neurological applications.3,4 Many of the potential benefits of MRI are limited only by availability of scanners and funding. For example, MR cholangiopancreatography could replace many diagnostic endoscopic cholangiopancreatograms. MR spectroscopy has tremendous potential for assessing tumour spread and recurrence, and an MRI-equipped operating theatre enabling perioperative guidance of surgical resection of tumour tissue is already a reality. It is also possible to guide and monitor percutaneous tumour ablation with MRI. New tissue-specific MR contrast agents, such as those taken up by lymph nodes, are likely to become available. This could lead to targeted therapy, with the therapeutic agent attached to a tissue-specific contrast agent. The next five years are likely to see expansion of the accepted applications for MRI.

Interventional radiology. Many recent advances relate to the increasing sophistication of hardware such as catheters, stents and embolisation materials. Percutaneous access to small vessels is now possible, expanding the range of therapeutic options (eg, stenting of intracranial arteries, treatment of intracranial aneurysms and thrombolytic therapy). Other innovations likely to affect therapeutic practices include imaging-guided radiofrequency tumour ablation, percutaneous aortic aneurysm stenting, percutaneous vertebroplasty, and uterine fibroid embolisation.

These emerging technologies need critical appraisal to avoid the risks attending uncontrolled introduction. Such "horizon scanning" by government agencies working with medical experts has been instituted in Australia and elsewhere. With such a choice of expensive imaging modalities, evidence-based guidelines are needed more than ever for cost-effective imaging. The education of clinicians is a priority of the Royal Australian and New Zealand College of Radiologists and is addressed by the latest edition of Imaging Guidelines.5