Radiographic film fog in the darkroom

One of the most common and yet also most preventable problems in the radiology department is unnecessary darkroom fogging of x-ray film, which can degrade image quality to the extent that the procedure must be repeated. Such problems can be overcome by identifying and eliminating sources of fog, such as incorrect safelight filters, excessive safelight wattage, using too many safelights or placing them too close to the work area, light leaks, and indicator lights on telephones, silver recovery units, timers, or other electrical devices.     

Radiological laser film scanner sampling artifact

Artifacts seen on laser digitized radiographs are analyzed and mathematically explained based on the concept of image contrast. Our investigation considered the following determinants: (a) laser spot size, (b) signal processing components, (c) image characteristics, and (d) observer performance. A functional relationship between the sampling interval, laser spot size, and the contrast of the artifact seen on the digitized image is derived. This relationship is verified experimentally using a variable spot size laser source and sampling at interval of 175.0 microns. The problem of digitizing artifact seen on film images obtained with anti-scatter grids is discussed.     

Influence of film fog on radiographic caries diagnosis

Increasing film speed may potentially jeopardize diagnostic quality because of a more rapid build up of fog and an ensuing decrease in image contrast. A standardized amount of fog was simulated by pre-exposing E-speed dental films before use to obtain images of extracted teeth with and without approximal caries. Three experiments were performed. In the first, no effort was made to compensate for the increased density caused by fog. In the other two, density was kept constant by reducing exposure and developing time respectively. Nine dentists recorded the presence and absence of caries using a rating scale to indicate diagnostic confidence. As a measure of diagnostic accuracy, the area under the binormal ROC curve was used and the values averaged across observers. The results showed that fog, up to a level of base plus fog of 0.6 optical density units, had no influence on the diagnostic accuracy in the absence of any compensation. When exposure was lowered to compensate for the increased density, significantly lower diagnostic accuracy was found. On the other hand, when developing time was decreased, no significant difference was found. Observers ranked radiographs with higher levels of fog as being of lower quality. However, no significant correlation was found between subjective ranking of image quality and diagnostic accuracy obtained from the same radiographs. It is concluded that relatively high levels of fog do not exert a negative influence on approximal caries diagnosis and no attempt should therefore be made to compensate for the increased density.     

Spontaneous pneumothorax caused by metastatic hemangioendothelioma. Radiographic appearance and pathologic correlation

A patient with hemangioendothelioma is described, who developed a metastatic pulmonary nodule, subsequently a bullous lesion contiguous to the nodule, and finally spontaneous pneumothorax. In such cases, newly formed bullous lesions may conceal originally visible metastatic foci and can be a potential source of spontaneous pneumothorax.     

Radiographic and CT findings of nontuberculous mycobacterial pulmonary infection caused by Mycobacterium abscessus

OBJECTIVE: The purpose of our study was to describe the radiographic and CT findings in patients with pulmonary infections caused by Mycobacterium abscessus, one of the more common rapidly growing nontuberculous mycobacteria that cause lung disease. CONCLUSION: The main radiologic and CT manifestations of M. abscessus lung infection are bilateral small nodular opacities, bronchiectasis, and cavity formation.     

Evaluation of new methods for removing moire artifact of radiochromic film

An optical interference-pattern, a moire artifact, is produced during the film scanning process using a flatbed scanner. Images with moire artifacts include optical density fluctuations thereby leading to inaccuracy of measurement. In this study, we proposed two methods for removing moire artifacts from radiochromic film and compared dose response and profile as well as image resolution and size between our proposed methods versus the conventional process. The proposed methods could remove the artifacts without impairing dosimetric performance. It is expected that the proposed methods facilitate more accurate film dosimetry with reflective radiochromic films.     

Radiographic visualization of left ventricular aneurysms on lateral chest film.

The diagnosis of left ventricular aneurysm on routine chest examination can be elusive. Six cases are presented which illustrate a radiographic sign not previously emphasized: a soft tissue border seen retrosternally or superiorly on lateral chest film produced by the wall of the aneurysm silhouetting against the midline cardiac shadow. This sign is not always present since it is dependent on the direction of projection of the aneurysm. However, when observed, it should suggest the proper diagnosis.     

Gibbs artifact reduction by nonnegativity constraint

This paper proposes a 2-step image reconstruction method in which the nonnegativity constraint in the iterative maximum-likelihood expectation maximization (MLEM) algorithm is used to effectively reduce Gibbs ringing artifacts. Methods: Gibbs artifacts are difficult to control during imaging reconstruction. The proposed method uses the postprocessing strategy to suppress Gibbs artifacts. In the first step, a raw image is reconstructed from projections without correction for point spread function (PSF). The attenuation correction can be performed in the first step by using, for example, the iterative MLEM or ordered-subsets expectation maximization (OS-EM) algorithm. The second step is a postprocessing procedure that corrects for the PSF blurring effect. If the target features (e.g., hot lesions) have a positive background, removing the background before application of the postprocessing filter significantly helps with target deblurring and Gibbs artifact suppression. This postprocessing filter is the image-domain MLEM algorithm. The background activity is attached back to the foreground after lesion sharpening. Results: Computer simulations and PET phantom studies were performed using the proposed 2-step method. The background removal strategy significantly reduced Gibbs artifacts. Conclusion: Gibbs ringing artifacts generated during image reconstruction are difficult to avoid if compensation for the PSF of the system is needed. The strategy of separating image reconstruction from PSF compensation has been shown effective in removal of Gibbs ringing artifacts.     

Removal of high signal artifact (marching metal artifact) by the magnetic substance

During this project, we evaluated methods to prevent high-signal artifact (marching metal artifact) that are caused by magnetic substance. Marching metal artifact is caused by the resonance frequency created by magnetic substance. Phase encoding and frequency encoding are often switched to minimize the influence that marching metal artifact have on the image. However, this method will only change the position at which marching metal artifact occur. It does not have the ability to completely prevent marching metal artifact. Our research illustrated that marching metal artifact can be prevented by changing the strength of the slice selective gradient field at the 90 degree RF pulse and 180 degree RF pulse. In other words, marching metal artifact can be prevented by changing the frequency bandwidth for the 90 degree RF pulse and 180 degree RF pulse. The incorporation of the phase correct option in the device used for our research (SIGNA LX and SIGNA CV/i) results in different slice selective gradient field strengths at the 90 degree RF pulse and the 180 degree RF pulse. This indicates that the use of phase correction enables marching metal artifact to be prevented.     

Erosive arthritis of the temporomandibular joint caused by Teflon-Proplast implants: plain film features

Six patients had osseous destructive changes of the temporomandibular joint after placement of Teflon-Proplast implants for treatment of internal derangements. The implants were surgically removed from all six joints, and foreign-body reactions were found to account for the radiographic appearance. The plain film radiographic features included single or multiple osseous erosions of the mandibular condyle in all cases and the temporal bone of the glenoid fossa in two cases. Some erosions were poorly defined, whereas others were well defined, either with or without sclerotic margins. Radiologists must be aware of this possible complication of alloplastic temporomandibular joint implants in order to suggest the diagnosis in the appropriate clinical setting.