Added Value of Ultra-low-dose Computed Tomography, Dose Equivalent to Chest X-Ray Radiography, for Diagnosing Chest Pathology

Abstract

Purpose: The purpose of this study was to assess the clinical value of ultra-low-dose computed tomography (ULDCT) compared with chest x-ray radiography (CXR) for diagnosing chest pathology.

Materials and methods: A total of 200 patients referred for CXR by outpatient clinics or general practitioners were enrolled prospectively. They underwent CXR (posteroanterior and lateral) and ULDCT (120 kV, 3 mAs) on the same day. In-room time and effective dose were recorded for each examination. Studies were categorized whether they were diagnostic or not, relevant radiologic diagnostic findings were reported, and confidence for diagnosis was recorded by a Likert scale. Differences in diagnostic confidence and effect on management decision were compared.

Results: In-room time was <2 minutes for CXR and <3 minutes for ULDCT. Effective dose was 0.040 mSv for CXR and 0.071 mSv for ULDCT. CXR was considered diagnostic in 98% and ULDCT in 100%. The mean perceived confidence for diagnosis was 88±12% with CXR and 98±2% with ULDCT (P<0.0001), whereas discrepant findings between CXR and ULDCT were found in 101 of 200 patients. As compared with CXR, ULDCT had added value for management decisions in 40 of 200 patients.

Conclusions: ULDCT provided added value to the radiologist by improved perceived confidence with a reduction in false-positive and false-negative CXR investigations that had management implications in 20% of patients. The effective dose of ULDCT will not be a limiting factor for introducing ULDCT of the chest on a broad scale in clinical practice.

FIGURE 1

A 72-year-old male patient with metastasized melanoma and immunotherapy with recent pneumonia has recurrent fever of 40°C (104°F). The clinical question was “pneumonia?” CXR posteroanterior (A, C) and lateral projections (B, D). Small residual lesion in the left lower lobe (A, B, arrow in A) from previous pneumonia that has been resorbed; there are no signs of active pneumonia. CXR perceived confidence for diagnosis was 95%. Pneumonia 6 weeks before (C, D, encircled). In-room time was 110 seconds, effective dose 0.03 mSv.

FIGURE 2

Same patient as in Figure 1. ULDCT from below, enlarged lymph nodes were excluded. Multiple foci with tree-in-bud aspect in the right lower lobe (A–C, encircled), not observed on CXR. A band-like density in the left lower lobe after previous pneumonia (B, C, arrow). ULDCT perceived confidence for diagnosis was 100%. Fever may be caused by immunotherapy itself, although the combination of illness, fever, and tree-in-bud pattern is likely active infection. The referring physician was contacted for expected therapeutic consequences. In-room time was 168 seconds, effective dose was 0.08 mSv.

FIGURE 3

A 70-year-old male patient with myasthenia gravis autoimmune disease. The clinical question was “pathology?” CXR posteroanterior (A) and lateral (B) projections. Two nodules project on the posteroanterior image (arrows), one possibly in the lower lobe on the lateral view (arrow) but for the other with location unsure (intrapulmonary or not), and the morphology could not be characterized. CXR perceived confidence was 50% for presence of intrapulmonary nodules. On CXR, there were no signs of thymus enlargement, although this could not be excluded. In-room time was 96 seconds, effective dose was 0.04 mSv.

FIGURE 4

Same patient as in Figure 3. ULDCT from below, showing multiple intrapulmonary smooth-walled nodules with certainty that were indeterminate on CXR (A–E, arrows). Differential diagnosis was nodules due to the autoimmune disease, or use of azathioprine medication, or infectious. Thymus hyperplasia or thymoma was excluded (F). ULDCT perceived confidence for diagnosis was 100%. ULDCT provides more information with better confidence. In-room time was 156 seconds, effective dose was 0.08 mSv.