Optimization of Digital Mammography Resolution Using Magnification Technique in Computed Radiography

PURPOSE: To determine whether magnified digital mammography using a computed radiography system can produce better spatial resolution by reducing the focus-object distance, and to define the optimal magnification factor when a large x-ray tube focal spot is used for digital mammography using a CR system. MATERIALS AND METHODS: Digital images obtained using computed radiography of a breast phantom were obtained using various magnification factors. Up to twelve acrylic blocks each measuring one centimeter in height were used to increase the distance between the breast phantom and the base plate (screen holder), in order to create the magnification images. The large (0.3 mm) focal spot of the x-ray tube was used for the entire series of images. Three radiologists participated in the evaluation of the images, in order to determine which had the best resolution. The resolving ability of the line pair structures and image clarity of the detectable artificial microcalcifications (specs) were the two factors used to determine the resolution of the images. The images were not compressed aFnd the viewing conditions, including the magnification factors, brightness and contrast, were fixed. The images were displayed on four high resolution PACS dedicated monitors (5 mega pixel LCD, BARCO Belgium). RESULTS: A focus-object distance of 590 mm and a source-to-image receptor distance of 650 mm (set by the manufacturer) resulted in the best resolution, when combined with a magnification factor of 1.1. All three radiologists agreed on this result. Two of the radiologists believed that at least two more line pairs were better separated on the magnified image having the best resolution than on the unmagnified image, while one radiologist believed that three more line pairs were better separated on this magnified image. Using images with still larger magnification factors did not improve the resolution due to edge blurring. It was easier to determine the resolving power by means of the line-pair structures than by assessing the clarity of the artificial microcalcifications (specs). A 10% decrease in focal spot-object distance resulted in a 21% increase in radiation to the breasts. CONCLUSION: Magnified digital breast images taken with a computed radiography system using a large focal spot produced better quality images, because of their utilizing more pixels per volume of the breast phantom with a minimal increase in radiation dosage.

Bronchiectasis: Diagnostic Accuracy of Chest Computed Radiography

PURPOSE: The aim of this study was to assess the diagnostic accuracy of chest comput-ed radiography for thedetection of bronchiectasis diagnosed by high-resolution CT. MATERIALS AND METHODS: Our study included 100consecutive patients with bronchiec-tasis and 20 normal subjects, all seen on high-resolution CT. Two independentobservers analyzed chest computed radiographs and recorded the presence and type of bronchiectasis, and the invo lved lobe. RESULTS: On high-resolution CT, bronchiectasis was seen in one lobe in 29 patients, two lobes in 29,three lobes in 16, four lobes in 14, five lobes in 10, and six lobes in t wo. The bronchiectasis was tubular in 55patients, mixed tubular and cystic in 29, and cystic in 16. For observer 1, the sensitivity, specificity, andaccuracy of chest com-puted radiography was 95%, 85%, and 93%, respective l y, while for observer 2, thecorresponding figures were 93%, 85%, and 92%. Sensitivity and specificity for observ-er 1 were 33% and 96% for theright upper lobe (46% and 95% for observer 2), 68% and 86% for the right middle lobe (76% and 86%), 70% and 78%for the right lower lobe (48% and 83%), 50% and 100% for the left upper lobe (50% and 97%), 63% and 90% for thelingular segment (49% and 93%), and 87% and 75% for the left lower lobe (75% and 90%), respective l y. Tubularbronchiectasis involving a single lobe was the most common source of false negative readings based on the findingsof chest com-puted radiography. CONCLUSION: Because chest computed radiography is not inferior to high-resolutionCT for the detection of bronchiectasis, the routine use of chest computed radiography in screening forbronchiectasis is feasible. Howeve r, due to its low sensitivity in detect-ing bronchiectasis in a specific lobe,preoperative high-resolution CT examination may be needed.

High-Resolution PACS Work station: Diagnostic Performance and Comparison with Laser-Printed CR Films in Chest Diseases

OBJECTIVES: To compare the diagnostic performance of a high-resolution picture archiving and communications system (PACS) workstation directly interfaced with computed radiography(CR) with laser-printed CR films in chest diseases. MATERIALS AND METHODS: Chest radiographs with (n=91) and without (n=25) abnormalities were included. Atotal of 100 abnormalities from 91 radiographs consisted of irregular lines, pneumothoraces, nodules and consolidations (25 of each). Laser-printed hard copies with dynamic range compression (DRC) were produced. InPACS, soft copies of 1760 X 2140 X 10 bits CR images were displayed on 1536 X 2048 with 8 bit gray-scale monitors.The performance of four observers was compared between laser-printed hard copies and CR images displayed on a workstation according to receiver operating characteristic analysis. RESULTS: Overall, no significant difference sin observer performance were observed between laser-printed hard copies and CR images displayed on a workstation(p=.2454). Even though statistically not significant, the former was slightly superior to the latter for lesions of irregular lines, pneumothoraces, and consolidations, whereas for nodules, the latter was slightly better than the former. CONCLUSION: The diagnostic performance of a high-resolution PACS workstation in chest radiographs is acceptable and comparable to CR hard copies printed with DRC processing mode.