Assessment of technical and biological parameters of volumetric quantitative computed tomography of the foot: a phantom study.

SUMMARY: Few studies exist for bone densitometry of the whole foot. A phantom study demonstrated the sources of error and necessary controls for accurate quantitative computed tomography of the foot. A loss in bone mineral density (BMD) in the small foot bones may be an early indicator of diabetic foot complications. INTRODUCTION: Volumetric quantitative computed tomography (vQCT) facilitates the assessment of pedal bone osteopenia, which, in the presence of peripheral neuropathy, may well be an early sign of diabetic foot deformity. To date, sources and magnitudes of error in foot vQCT measurements have not been reported. METHODS: Foot phantoms were scanned using a 64-slice CT scanner. Energy (in kilovoltage peak), table height, phantom size and orientation, location of "bone" inserts, insert material, location of calibration phantom, and reconstruction kernel were systematically varied during scan acquisition. RESULTS: Energy (in kilovoltage peak) and distance from the isocenter (table height) resulted in relative attenuation changes from -5% to 22% and -5% to 0%, respectively, and average BMD changes from -0.9% to 0.0% and -1.1% to 0.3%, respectively, compared to a baseline 120-kVp scan performed at the isocenter. BMD compared to manufacturer-specified values ranged, on average, from -2.2% to 0.9%. Phantom size and location of bone-equivalent material inserts resulted in relative attenuation changes of -1.2% to 1.4% compared to the medium-sized phantom. CONCLUSION: This study demonstrated that variations in kilovoltage peak and table height can be controlled using a calibration phantom scanned at the same energy and height as a foot phantom; however, error due to soft tissue thickness and location of bones within a foot cannot be controlled using a calibration phantom alone.

Detection of CT-proved pulmonary nodules: comparison of selenium-based digital and conventional screen-film chest radiographs.

PURPOSE: To compare hard-copy digital chest radiographs obtained with a selenium-based system with wide-latitude asymmetric screen-film radiographs for detection of pulmonary nodules. MATERIALS AND METHODS: Fifty patients undergoing thoracic computed tomography (CT) for suspected pulmonary nodules were recruited to undergo both digital and screen-film posteroanterior (PA) and lateral chest radiography. Three chest radiologists blinded to the CT results independently reviewed each digital and screen-film radiograph, identified each nodule, and graded their confidence for its presence. RESULTS: Seventy-eight pulmonary nodules (mean diameter, 1.5 cm; range, 0.5-3.5 cm; 62 soft tissue, 16 calcified) were identified with CT in 34 patients, while 16 patients had clear lungs. The mean sensitivity for the detection of all nodules by all readers (PA and lateral) was 66% (95% Cl, 54%, 76%) for digital radiographs and 64% (95% Cl, 52%, 74%) for screen-film radiographs. Differences between the two techniques were not statistically significant (P > .05, Student t test). There was no difference in mean false-positive-true-positive ratios (PA, 0.35; lateral, 0.53) or positive predictive values (PA, 74%; lateral, 65%), and no significant difference (P > .05) was seen in mean reader confidence rating. CONCLUSION: In detecting pulmonary nodules, radiologists perform comparably with selenium-based digital and wide-latitude asymmetric screen-film radiographs.

Soft-copy versus hard-copy cranial sonography: intraobserver agreement and workstation efficiency.

OBJECTIVE: The objective of the study was to determine the intraobserver agreement, confidence level, and efficiency in interpretation of soft-copy (workstation) versus hard-copy (laser-printed film) sonograms of the cranium. MATERIALS AND METHODS: Cranial sonograms of 100 premature infants were randomly reviewed twice on both soft-copy and hard-copy images by three observers and were graded for hemorrhage using a five-level scale. The kappa statistic was calculated to measure intraobserver agreement. Differences in agreement were tested for statistical significance with a test for marginal homogeneity. Observers rated their confidence in interpretation using a six-point ordinal scale. Total viewing time was recorded, and videotaped sessions were analyzed for image handling time (opening each case, closing each case, and selecting the next case) and interpretation time. RESULTS: For soft copy versus hard copy, the mean kappa value was .73; for hard-copy 1 versus hard-copy 2, .71; and for soft-copy 1 versus soft-copy 2, .65. None of these differences was statistically significant (p > .05). The mean confidence score was the same for soft copy (5.3) and hard copy (5.3). On average, the observers needed 24 min longer to review 100 studies on soft copy than on hard copy. Opening and closing times for soft copy were significantly faster than for hard copy (p = .0001); however, case selection for soft copy, which was not needed for hard copy, took 4.69-9.09 sec per case. Extrapolated to 100 cases, case selection accounted for 8-15 min of viewing time. CONCLUSION: Radiologist agreement and confidence in the interpretation of cranial sonograms for hemorrhage was the same for soft copy and hard copy. However, viewing times were longer for soft copy. Elimination of inefficiency in case selection could improve image-handling time.

Chest radiography: depiction of normal anatomy and pathologic structures with selenium-based digital radiography versus conventional screen-film radiography.

PURPOSE: To compare the subjective visibility of normal anatomy and pathologic structures in the chest on conventional screen-film radiographs versus selenium-based digital radiographs. MATERIALS AND METHODS: Screen-film and digital standard posteroanterior (PA) and lateral chest radiographs were obtained in 49 patients (32 men, 17 women; mean age, 60 years; range, 24-91 years) undergoing chest computed tomography (CT). Conventional images were phototimed at 115 kVp with use of a wide-latitude screen-film system and an antiscatter grid. Digital images were obtained at 150 kVp with use of a commercial system with a selenium detector and an air gap alone for scatter reduction. The image sets were independently compared by four radiologists, and the relative visibility of anatomic and pathologic features (proved at CT) was graded. Statistical significance (P < .0028) was evaluated with a one-tailed t test. RESULTS: Visibility with the digital images was statistically significantly increased for 11 of 13 normal anatomic features and for pathologic structures in the lung, soft tissue, and bone. CONCLUSION: Subjective visibility of pathologic structures and most normal anatomic features in the thorax was statistically significantly improved with selenium-based digital chest radiography compared with conventional screen-film chest radiography.

Quality monitoring of soft-copy displays for medical radiography.

As presentation of medical radiographic images on soft-copy displays (cathode ray tubes) becomes increasingly prevalent in electronic radiography, methods of quality assurance must be developed to ensure that radiologists can effectively transfer film-based reading skills. Luminance measurements provide the basis for evaluating the state of soft-copy displays. An integrated approach has been implemented at Mallinckrodt Institute of Radiology (MIR, Washington University, St Louis, MO) that facilitates measurement of geographically distributed soft-copy displays with centralized data logging, performance tracking, and calibration. MIR's central radiology image manager exercises the display station that drives the monitor, harvests the measurement data, stores the results, and submits the resulting data for additional processing. The luminance measurements are collected by a small, portable, photometric instrument designed at MIR that includes a serial port that is accessed via local area terminal service supported by the radiology image manager. The design details of the photometric instrument and example luminance characteristics of several soft-copy displays used at MIR are presented in this report.