An evaluation of single exposure dual energy subtraction chest radiography in screening for lung metastases

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An evaluation of single exposure dual energy subtraction chest radiography in screening for lung metastases


Author: Wong, Yee-ha
Title: An evaluation of single exposure dual energy subtraction chest radiography in screening for lung metastases
Degree: M.Sc.
Year: 2000
Subject: Chest -- Radiography
Lungs -- Radiography
Lungs -- Cancer -- Diagnosis
Metastasis -- Diagnosis
Hong Kong Polytechnic University -- Dissertations
Department: Multi-disciplinary Studies
Dept. of Optometry and Radiography
Pages: xv, 172 leaves : ill. ; 30 cm
Language: English
InnoPac Record:
Abstract: Pulmonary metastases that presented as metastatic nodules are commonly seen in patient with known malignancies. There are no signs and symptoms noted in patient with metastatic nodules in early stage and detection mainly relies on the capability of imaging tool to demonstrate the presence of nodule. Traditionally, conventional chest x-ray and Computed Tomography (CT) are the imaging tools used for screening of metastatic disease. Both techniques have their own advantages and disadvantages. Conventional chest x-ray is cheap, simple and readily accessible, but low in sensitivity. CT, on the other hand, is sensitive, but expensive and lower in specificity than conventional chest x-ray. Single-exposure dual energy (SEDE) subtraction chest radiography is a digital subtraction imaging technique that applies in projection chest radiography recently with the development of the storage phosphor imaging plates. A number of studies shown that SEDE has several advantages in the detection and characterization of pulmonary nodules over conventional chest radiography. The digital nature of SEDE and the simplification of lung field through removal of overlying rib shadows greatly improve the detectability of metastatic nodules. Also, the tissue-subtracted image of SEDE provides an assessment of calcium content of detected nodule and assists in making a more accurate differential diagnosis. Comparing with CT, SEDE is a simple, easily accessible and lower radiation dose imaging method. Routine CT protocol may offer little advantage over SEDE in screening for lung metastases. In the present study, the diagnostic accuracy of SEDE was compared with CT (a local protocol) in screening patients for lung metastases. A total of 94 patients of mean age 50.4 with known malignancies, who had both CT and SEDE of the chest, were recruited prospectively and retrospectively. Forty-five cases were with metastatic nodules and forty-nine cases were without. Total number of nodules noted in diseased cases were 299 with a mean of 6.6 nodules per subject. Four radiologists were invited as readers to participate in a Receiver Operating Characteristic (ROC) analysis and a comparison of nodule detection using CT and SEDE. Results show that there is no significant difference in the areas under the composite ROC curves of both CT and SEDE using paired t-test (p < 0.05). This means that both CT and SEDE are equal in performance in detecting the presence of metastatic disease with respect to the sample under study. One of the reasons that may account for their equal in performance is that the SEDE images allow good detection of metastatic nodules, especially those in the periphery and obscured by overlying ribs. However, CT demonstrates significantly more nodules than SEDE. SEDE shows only 46.5% of the total nodules noted by CT with lowest detection rate (12.5%) for nodules smaller than 0.5cm. The finding indicates a limitation of SEDE in identifying the exact number of nodules in patients with lung metastases. For patients that present with minute metastatic nodules, CT would be better than SEDE. Also in selected patients planning for complete surgical resection of metastatic nodules, CT would provide more detailed information on nodule number and location.

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