CT computer-aided volumetry fast tracks pneumothorax measurement

Potential deadly traumatic pneumothoraces can be measured in the emergency room with a computer-aided volumetric technique that helps move patients from diagnosis to treatment many times faster than conventional visual assessments of the condition with multislice CT.

The new approach, developed at Massachusetts General Hospital, has potential implications for the 30% to 39% of chest trauma patients who develop pneumothorax. Traditionally, radiologists have measured the extent of the condition manually, a task that can take as long as an hour. To aid evaluations, MGH researchers developed a computer-aided volumetry that quantifies pneumothoraces appearing on the patient's CT images in about three minutes.

The tool will help radiologists provide information quickly to surgeons to aid in decision making. It could replace x-ray and ultrasound for diagnosing the condition, said Wenli Cai, Ph.D, an assistant computer scientist in the MGH 3D imaging lab.

In a study reported in the March issue of the American Journal of Roentgenology (2009;192:830-836), Cai and colleagues applied the technique to three pigs and 68 trauma patients with at least one diagnosed occult pneumothorax. The computer-aided volumetry method extracted the pleural region, detected pneumothorax candidates, applied the dynamic thresholding model, reduced false-positive findings, and reported the volumetric measurement of pneumothoraces.

Researchers visually examined CT scans to identify and calculate the size of 83 pneumothoraces. Each identified pneumothorax was manually contoured. Nearly half were less than 10 mL, but they ranged in volume from 1 to 872 mL.

Cai found that the computer-aided method matched the accuracy of the manual approach. The computer-aided measures were performed in about three minutes, compared with 30 minutes to an hour for the manual approach.

Sensitivity for the computer-aided assessment was 100%, with a false-positive rate of 0.15 per case for 32 occult pneumothoraces that were larger than 25 mL. It performed flawlessly for pneumothoraces that were larger than 50 mL.

The treatment of pneumothoraces depends on the patients' symptoms, but size is emerging as a criterion for treatment, Cai said.

"Our computer-aided system will provide radiologists with precise and automated measurement of the size of pneumothoraces; it will also provide an important criterion in the decision-making process of chest tube drainage. Such a tool will improve patient care by reducing unnecessary treatments of pneumothoraces and will save the healthcare cost," he said.

Cai envisions situations in which computer-aided assessment can help avoid unnecessary surgeries. It could help rule out surgeries when the pneumothorax is small and the patient is stable. It could also monitor pneumothorax size over several days to determine when surgery is required, he said.

Whether precise measurement will tangibly improve clinical outcomes, however, remains a matter for discussion. Dr. Bruce Maycher, director of pulmonary radiology at St. Boniface General Hospital in Winnipeg, MB, noted in an interview with Diagnostic Imaging that pneumothorax is an easy diagnosis to make with CT. Its exact measurement is not strictly necessary.

"I think small, medium, and large might be as much as they really need to know. There are so many other things that are going to influence whether they drain that in terms of stability of the patient," he said.

But computer-aided volumetry could help the radiologist assess fluids, Maycher said.

"I could see more people wanting to know how much fluid is in the chest, not specifically for trauma but any cause of pleural effusion," he said.

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