Another basic principle that is being used to further drive development of CAD applications is the detection of pathologies based on variations in lumen diameter. CT colonoscopy has provided an ideal platform for virtual-navigation CAD, and the same concepts are being applied for detection of transition points of small bowel obstructions.

CAD ROLE IN ER

In terms of research, the exploration of CAD applications in ER is relatively new. A realization of the potential importance of computer-aided principles in emergency radiology is too recent for much data to have been disseminated broadly. Its popularity has been restricted to various conference platforms so far, and data may be waiting in the pipeline for publication.

CAD's potential for detecting intracranial bleeding sites and pulmonary embolism has been established by studies recently published in various journals. However, an interesting array of emergencies in which the new role of CAD is gaining momentum deserves special mention.

• Pneumothorax. The importance of automated detection and quantification of pneu-mothorax received prominent recognition at the 2007 RSNA meeting.⁸ Assigning CAD to use a range of Hounsfield units on MSCT data sets for mapping free air in the pleura of trauma patients revealed promising accuracy in quantification of pneumothorax and also highlighted the time savings. With computer-aided automated volume-try finding a strong correlation coefficient—nearly 0.9—between the clinical score and manually measured free air in pleural space, promising results are eagerly anticipated.

Results already achieved have encouraged researchers to go a step further and test CAD performance for quantifying pneumothorax in emphysematous patients and work on erroneous mapping of emphysematous bullae present in the lung. Clinicians wishing to ensure clinical stability may continue to place a chest tube.

This may sound discouraging for those attempting to develop CAD's ability to quantify free air in the pleura, but CAD can still play a role in the emergency room for monitoring of a relatively stable patient with a small pneumothorax. Other potential roles include situations just beginning to be explored, such as post-lung biopsy. Here, the idea is to avoid an invasive procedure in an otherwise stable patient.

• Pulmonary embolism. PE is a life-threatening emergency requiring prompt diagnosis to ensure a good clinical outcome. It is the only condition routinely encountered in the emergency setting for which the use of CAD has been extensively investigated.^9,10 Newer computer-aided detectors have the ability to automatically map tiny clots, even in the sixth-order branches of pulmonary vasculature. With the recent advances in scanners and scanning techniques, sensitivity has been as high as 85%. Specificity has ranged between 90% and 95%.