Objective: Compare low dose (50 mA) and standard dose (300 mA) MDCT in detection of metastatic pulmonary nodules in extrathoracic malignant patients in Siriraj hospital.
Material and method: Prospectively, 58 patients underwent chest CT examinations by 64-slice MDCT in non-enhanced phase with a reduced tube current of 50 mA (low-dose CT (LDCT)), followed by contrast-enhanced phase with a standard tube current of 300 mA (Standard-dose CT (SDCT)). Otherparameter such as tube voltage 120 kVp, spiral pitch 0.984, and section thickness 1.25 mm, were kept constant. Four hundred twenty two nodules found by SDCT and 427 nodules found by LDCT were analyzed.
Results: The sensitivity of LDCT was 94.7% for all nodules, 79% for nodules < or =2 mm, 94.2% for nodules 2.1-3 mm, 97% for nodules 3.1-4 mm, and 100% for nodules 4.1-5 mm. Three types of nodules were found and classified as calcific nodule, non-calcific nodule, and ground-glass nodule of which sensitivity for detection in LDCT were 100% (p = 1.000), 95.9% (p = 0.337) and 77% (p = 0.581), respectively. Most common causes of discrepancy in SDCT were unseen nodules and in LDCT were end-on vessel nodules. Majority of discrepant nodules and retrospective nodules were < or =3 mm. Effective dose ranged from 0.78 mSv.-1.6 mSv in LDCT and 4.22-9.57 mSv in SDCT.
Conclusion: There is no statistical difference in detection of metastatic pulmonary nodules by using low-dose and standard-dose CT images. Low-dose CT images can used to follow-up the treatment responsiveness of the known patient, diagnosed to have pulmonary metastasis.