Radiology: Digital tomo outperforms x-ray in TB patients

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Digital tomosynthesis provided greater accuracy in the depiction of lung lesions among patients with pulmonary mycobacterial disease, according to a study published in the October edition of Radiology.

Timely detection of pulmonary cavities is essential for effective treatment of cavitary pulmonary tuberculosis. However, sputum smear conversion is lengthy, and CT presents a high radiation dose burden. Chest x-ray, the first choice for diagnosis and follow-up, is limited by low sensitivity and specificity.

Researchers at Yonsei University Medical College in Seoul, South Korea hypothesized that the better depth resolution and reduced anatomic overlap of digital tomosynthesis (DTS) might improve detection of pulmonary lesions. The authors compared the diagnostic performance of low-dose DTS, which reduces the standard tomosynthesis dose from 0.12 mSv to 0.05 mSv, with conventional radiography in the detection of lung lesions with pulmonary mycobacterial disease.

The research team, led by Eun Young Kim, MD, of the department of radiology, recruited 65 patients with primary tuberculosis or another nontuberculosis mycobacterial disease from March to June 2009. The 32 males and 33 females (mean age, 50 years) had undergone regular CT studies. A group of 35 lesion-free patients (mean age, 54 years) served as the control group.

Two chest radiologists with 10 and three years of chest CT experience, respectively, and two years and six months of DTS experience, respectively, independently reviewed randomized image data. Radiologists were instructed to record each finding of pulmonary mycobacterial disease on the x-ray and DTS images in a blinded manner, according to the researchers.

The study employed CT as the reference standard. Researchers compared sensitivity, specificity, and accuracy of DTS and x-ray for the detection of mycobacterial disease and calculated and compared five patterns of lung abnormality—bronchiolitis, nodules, consolidation, cavities and volume loss--with CT on a per-patient basis.

According to researchers, overall accuracies of DTS and x-ray were 97 percent and 89 percent, respectively, for observer 1, and 99 percent and 93 percent, respectively, for observer 2. Thus, overall accuracy of DTS was significantly higher than radiography. Interobserver agreement for DTS was good to very good and superior to x-ray, continued the authors. The radiologists detected a mean of 108 cavities with DTS vs. a mean of 27 with radiography, offered the researchers.

The authors acknowledged that the study did not include analysis of clinical data or evaluate patient symptoms, but suggested that the study was not designed to evaluate DTS as a tool to predict disease. They also cited cost differences among CT ($200), DTS ($30) and x-ray ($10) in South Korea.

Low-dose DTS is superior to radiography for the detection of lung lesions, especially cavitary lesions, in patients with pulmonary mycobacterial disease, concluded the researchers, who added that early detection might accelerate selection of appropriate therapy and facilitate prediction of the patient’s prognosis.