Carl E. Ravin

Air crescent sign of invasive aspergillosis.

Pulmonary infection in immunocompromised patients is frequently difficult to diagnose. Therapy for the more common pathogens differs greatly from that for infection with unusual opportunistic organisms. However, neither of these infectious agents offers specific radiographic signs. The authors report on 4 patients with acute leukemia and invasive aspergillosis whose radiographs demonstrated a distinctive feature of one or more air crescents within an area of pulmonary infiltrate. Autopsy studies correlated the radiographic changes with an infection due to Aspergillus species fungi. While the sign is not pathognomonic for Aspergillus infection, seen in a suitable host, it would suggest the possibility of invasive aspergillosis.

Accuracy of the chest radiograph in diagnosis of pulmonary embolism.

In an effort to determine the sensitivity and specificity of the chest roentgenogram for the diagnosis of pulmonary embolism, roentgenograms of 152 patients who were all suspected of having pulmonary embolism were randomized and presented to nine interpreters. One hundred eight patients in the series were proven to have pulmonary embolism on the basis of a positive pulmonary angiogram. Forty-four patients were assumed not to have embolism on the basis of either a normal perfusion isotope scan or a pulmonary angiogram which did not show embolism. The interpreters were requested to indicate whether pulmonary embolism was present or absent, or whether they could not tell from the roentgenogram. Readers had no prior knowledge of the actual disease state. The average true-positive ratio, (sensitivity) was 0.33, with a range of 0.52 to 0.88. The average true-negative ratio (specificity) was 0.59, with a range of 0.31 to 0.80. The false-positive and false-negative ratios were respectively, 0.21 (range 0.05 to 0.39) and 0.41 (range 0.15 to 0.70). A predictive index, reflecting the overall accuracy of diagnosis, was calculated for the entire group and was 0.40, with a range of 0.17 to 0.57. There appeared to be no correlation between training or experience and accuracy of performance in this study.

Radiographic recognition of pneumothorax in the intensive care unit.

Recognizing pneumothorax and hydropneumothorax on chest x-rays of supine ICU patients requires attention to areas other than the lung apex. Pleural air in a supine patient collects in the anterior costophrenic sulcus, producing hyperlucency over the upper abdominal quadrants, and the deep costophrenic sulcus sign. Hydropneumothorax may be recognized when a sharp pleural line is bordered by increased opacity within the pleural space. The presence of pneumothorax and hydropneumothorax can be confirmed by decubitus or upright chest x-rays.

Radiation Dose for Body CT Protocols: Variability of Scanners at One Institution

OBJECTIVE The objective of our study was to determine, using an anthropomorphic phantom, whether patients are subject to variable radiation doses based on scanner assignment for common body CT studies. MATERIALS AND METHODS Twenty metal oxide semiconductor field effect transistor dosimeters were placed in a medium-sized anthropomorphic phantom of a man. Pulmonary embolism and chest, abdomen, and pelvis protocols were used to scan the phantom three times with GE Healthcare scanners in four configurations and one 64-MDCT Siemens Healthcare scanner. Organ doses were averaged, and effective doses were calculated with weighting factors. RESULTS The mean effective doses for the pulmonary embolism protocol ranged from 9.9 to 18.5 mSv and for the chest, abdomen, and pelvis protocol from 6.7 to 18.5 mSv. For the pulmonary embolism protocol, the mean effective dose from the Siemens Healthcare 64-MDCT scanner was significantly lower than that from the 16- and 64-MDCT GE Healthcare scanners (p < 0.001). The mean effective dose from the GE 4-MDCT scanner was significantly lower than that for the GE 16-MDCT scanner (p < 0.001) but not the GE 64-MDCT scanner (p = 0.02). For the chest, abdomen, and pelvis protocol, all mean effective doses from the GE scanners were significantly different from one another (p < 0.001), the lowest mean effective dose being found with use of a single-detector CT scanner and the highest with a 4-MDCT scanner. For the chest, abdomen, and pelvis protocols, the difference between the mean effective doses from the GE Healthcare and Siemens Healthcare 64-MDCT scanners was not statistically significant (p = 0.89). CONCLUSION According to phantom data, patients are subject to different radiation exposures for similar body CT protocols depending on scanner assignment. In general, doses are lowest with use of 64-MDCT scanners.

Fundamental imaging characteristics of a slot-scan digital chest radiographic system

Our purpose in this study was to evaluate the fundamental image quality characteristics of a new slot-scan digital chest radiography system (ThoraScan, Delft Imaging Systems/Nucletron, Veenendaal, The Netherlands). The linearity of the system was measured over a wide exposure range at 90, 117, and 140 kVp with added Al filtration. System uniformity and reproducibility were established with an analysis of images from repeated exposures. The modulation transfer function (MTF) was evaluated using an established edge method. The noise power spectrum (NPS) and the detective quantum efficiency (DQE) of the system were evaluated at the three kilo-voltages over a range of exposures. Scatter fraction (SF) measurements were made using a posterior beam stop method and a geometrical chest phantom. The system demonstrated excellent linearity, but some structured nonuniformities. The 0.1 MTF values occurred between 3.3-3.5 mm(-1). The DQE(0.15) and DQE(2.5) were 0.21 and 0.07 at 90 kVp, 0.18 and 0.05 at 117 kVp, and 0.16 and 0.03 at 140 kVp, respectively. The system exhibited remarkably lower SFs compared to conventional full-field systems with anti-scatter grid, measuring 0.13 in the lungs and 0.43 in the mediastinum. The findings indicated that the slot-scan design provides marked scatter reduction leading to high effective DQE (DQEeff) of the system and reduced patient dose required to achieve high image quality.

Textbook of diagnostic imaging

Three volumes provide information organized by major topics covering the state-of-the-art for all imaging procedures. It includes coverage of the fundamentals of diagnostic imaging, and a system-by-system approach.

Detector or System? Extending the Concept of Detective Quantum Efficiency to Characterize the Performance of Digital Radiographic Imaging Systems

PURPOSE To develop an experimental method for measuring the effective detective quantum efficiency (eDQE) of digital radiographic imaging systems and evaluate its use in select imaging systems. MATERIALS AND METHODS A geometric phantom emulating the attenuation and scatter properties of the adult human thorax was employed to assess eight imaging systems in a total of nine configurations. The noise power spectrum (NPS) was derived from images of the phantom acquired at three exposure levels spanning the operating range of the system. The modulation transfer function (MTF) was measured by using an edge device positioned at the anterior surface of the phantom. Scatter measurements were made by using a beam-stop technique. All measurements, including those of phantom attenuation and estimates of x-ray flux, were used to compute the eDQE. RESULTS The MTF results showed notable degradation owing to focal spot blur. Scatter fractions ranged between 11% and 56%, depending on the system. The eDQE(0) results ranged from 1%-17%, indicating a reduction of up to one order of magnitude and different rank ordering and performance among systems, compared with that implied in reported conventional detective quantum efficiency results from the same systems. CONCLUSION The eDQE method was easy to implement, yielded reproducible results, and provided a meaningful reflection of system performance by quantifying image quality in a clinically relevant context. The difference in the magnitude of the measured eDQE and the ideal eDQE of 100% provides a great opportunity for improving the image quality of radiographic and mammographic systems while reducing patient dose.

Effective DQE (eDQE) and speed of digital radiographic systems: An experimental methodology

Prior studies on performance evaluation of digital radiographic systems have primarily focused on the assessment of the detector performance alone. However, the clinical performance of such systems is also substantially impacted by magnification, focal spot blur, the presence of scattered radiation, and the presence of an antiscatter grid. The purpose of this study is to evaluate an experimental methodology to assess the performance of a digital radiographic system, including those attributes, and to propose a new metric, effective detective quantum efficiency (eDQE), a candidate for defining the efficiency or speed of digital radiographic imaging systems. The study employed a geometric phantom simulating the attenuation and scatter properties of the adult human thorax and a representative indirect flat-panel-based clinical digital radiographic imaging system. The noise power spectrum (NPS) was derived from images of the phantom acquired at three exposure levels spanning the operating range of the clinical system. The modulation transfer function (MTF) was measured using an edge device positioned at the surface of the phantom, facing the x-ray source. Scatter measurements were made using a beam stop technique. The eDQE was then computed from these measurements, along with measures of phantom attenuation and x-ray flux. The MTF results showed notable impact from the focal spot blur, while the NPS depicted a large component of structured noise resulting from use of an antiscatter grid. The eDQE was found to be an order of magnitude lower than the conventional DQE. At 120 kVp, eDQE(0) was in the 8%-9% range, fivefold lower than DQE(0) at the same technique. The eDQE method yielded reproducible estimates of the system performance in a clinically relevant context by quantifying the inherent speed of the system, that is, the actual signal to noise ratio that would be measured under clinical operating conditions.

Quantitative scatter measurement in digital radiography using a photostimulable phosphor imaging system

X-ray scatter fractions measured with two detectors are compared: a photostimulable phosphor system (PSP) and a conventional film-screen technique. For both detection methods, a beam-stop technique was used to estimate the scatter fraction in polystyrene phantoms. These scatter fraction measurements are compared to previously reported film-based measurements. Scatter fractions obtained with the PSP were in good agreement both with measurements using film as well as with most previously reported measurements. For the PSP measurements, repeatability was better than 1%. It was found that the PSP provides a precise x-ray detector for quantitative scatter measurement in digital radiography.

Calcification in pulmonary metastases

A large variety of neoplasms can produce calcified lung metastases. Three unusual examples are presented and the relevant literature is reviewed. Each case involves a neoplasm not previously reported to produce calcified lung metastases: malignant mesenchymoma, fibrosarcoma of the breast, and medullary carcinoma of the thyroid. The sarcomas are reported in the literature to develop calcified lung metastases are osteogenic sarcoma, chondrosarcoma, synovial sarcoma, and giant cell tumour. Among carcinomas, the papillary and mucinous adenocarcinomas are the histological types most likely to develop calcified lung metastases. The metastases of a number of other tumours have calcified after antineoplastic therapy. Calcification in metastases arises through a variety of mechanisms: bone formation in tumour osteoid, calcification and ossification of tumour cartilage, dystrophic calcification and ossification of tumour cartilage, dystrophic calcification and mucoid calcification. Since calcified lung metastases can strongly resemble granulomas or hamartomas, a reasonable suspicion of malignancy is necessary when evaluating calcified pulmonary nodules.