1. Chest X-rays: For an Overview with ILO Grading:
The ILO grading system is based upon the PA or frontal radiograph. Additional oblique and lateral views are always helpful, but not required by the ILO grading system, although if involved in a bankruptcy trust claim, apparently some trusts are requiring PA and lateral chest x-ray views. The chest x-ray gives a good overview of the lungs and chest cavity anatomy and can show imaging findings/markers or lack thereof of asbestos disease. However, asbestos marker identification is more difficult in obese and very large individuals and in general there can be missed or poorly seen findings, such as lack of visualization of plaques or their calcifications, lack of visualization of emphysema and missed small cancer nodules (under calls); confusing and misleading findings, such as other disease states looking like, but not caused by asbestosis; or fat along that lateral chest walls in heavyset individuals that mimics non-calcified pleural plaques (over calls). That is why supine spiral CT and supine and Prone HRCT are so useful in clarifying and better defining the presence or absence of imaging markers of asbestos disease.
My protocols call for a single PA upright chest x-ray when doing basic screening; PA upright and left lateral chest x-rays, if demanded by a trust or referring physician and 4 views of the chest – PA upright, left lateral and both 45 degree obliques when doing a comprehensive asbestos chest x-ray evaluation.
2. Supine Spiral CT and Supine HRCT: For Plaques and Cancer Screening:
Supine spiral CT and supine HRCT scans in the supine (lying on one’s back) position are more definitive with less false negatives (under calls) and less false positives (over calls) than the chest x-rays for showing asbestos imaging related markers. They are best utilized to look for pleural plaques and/or cancers. They identify moderate-to-severe, but not mild interstitial changes having the appearance and distribution of asbestosis. Therefore, in identifying asbestos markers in benign or cancer cases, supine spiral CT and supine HRCT studies add valuable information which may have been missed and under called; been misleading or overcalled by chest x-ray. In cancer cases, when plaquing is either not or poorly identified on chest x-rays or their calcifications are equivocal or not seen, when there is smooth chest wall thickening in a large person perhaps representing fat rather than plaques and there has been a smoking history, it is optimal to obtain, when possible, a copy of one or multiple CT scans, as any one of the CT scans should be adequate, especially those prior to surgery, at showing the presence or absence of pleural plaquing and their calcifications, differentiating chest wall fat from plaques and identifying the presence or absence of most cases of emphysema. Supine HRCT is even more accurate at showing small plaques and any plaque associated calcifications and in giving further detail to emphysema or a nodule(s). If moderate or severe asbestosis is suspect, try to obtain CT scans prior to or at the early stages of the cancer and prior to chemotherapy or radiation treatment, which may or may not, in and of themselves, cause lung scarring.
My protocols for comprehensive scanning are to obtain supine spiral CT, 5 mm thick, 5 mm apart with multiple reformations including supine axial HRCT, utilizing 1.25 mm thick slices, 1.25 mm apart; routine sagittal and coronal reformations, usually 2 to 2.5mm thick slices, 2 to 2.5 mm apart and axial and coronal maximum (for nodules) and axial minimum (for emphysema) intensity projection reformations. It is critical that the supine spiral CT, supine HRCT and the coronal and sagittal reformations all are dual processed – that is shown in both the high resolution lung algorithm (“Bone” on the General Electric scanner) for optimal lung detail and the smoothed, chest wall/mediastinal algorithm (“Standard” on the General Electric scanner) for optimal plaque detail and nodule screening including identifying or excluding calcification in the nodule. The high resolution algorithm can cause the chest walls to have a thin bright line about them and makes small plaques and their calcifications difficult to interpret and can prevent the differentiation of calcified from non-calcified small nodules as they all can look bright or often falsely calcified. The chest wall/mediastinal algorithm causes slight blurring and smoothing of image information and is less pixely, however, it reduces the definition of lung information for fine interstitial changes and emphysema. No contrast is given as this has an allergy risk, including death, is more costly and can cause false positive appearances of punctate calcified plaques, that are nothing more than enhanced vessels-on-end seen adjacent to the chest walls or more elongated and thin plaques that are nothing more than enhanced vessels running in the extra pleural fat.
3. Prone HRCT: To Identify Low Profusion/Mild Asbestosis:
Gravitational or dependent density or haziness occurring at the back bottoms of the lungs, is often seen on supine spiral CT or supine HRCT scans. This gravitational density occurs due to the gravitational downward pressure from the anterior and mid portions of the lungs onto the posterior aspects of the lungs, resulting in a) their partial collapse or gravitationally-caused atelectasis and to b) blood pooling. The problem is, that early asbestosis occurs at the back bottoms of the lungs too and, therefore, in the supine position one cannot determine whether this haziness is due to gravitational changes versus due to true scarring from asbestosis or other interstitial diseases or a combination of both. Therefore, it is important to have the individual lie in the prone positon (on his/her stomach) and have the gravitational dependent density moved away from the back of the lungs, to the front of the lungs, in order to visualize any non-gravity caused interstitial lung changes in the back bottoms of the lungs. HRCT is preferred to CT because of its thinner slice thickness and high resolution. Therefore, when screening for mild asbestosis in benign and malignant disease; in working up difficult cases with equivocal or negative chest x-rays or in trying to confirm the presence of interstitial disease as opposed to emphysema or other causes, the prone HRCT is the ideal way to look for mild asbestosis. Because the prone HRCT often only samples the lungs and does not use contiguous slices, in most cases (there are skipped spaces between slices to avoid excessive radiation dose), it is not ideal for screening for all plaques and cancers, since if they are small, they can be missed and skipped over by the skipped spacing between slices. In all cancer cases, when possible, if the individual is early on in his/her disease state and does not already have evidence for moderate to severe asbestosis, try to obtain a prone HRCT. The reason being, that this test will show the imaging presence or absence of mild interstitial lung disease, having the appearance and distribution of asbestosis. Later on, it will be more difficult for the individual to cooperate, and there will be other interventions that have occurred including surgery and potential radiation or chemotherapy, which might interfere with or change the interstitial findings.
My protocols ask for prone HRCT images, 1.25 mm thick, 15 mm apart (some use 5 mm or 10mm apart). Processed in both the high resolution lung algorithm (“Bone” on the General Electric scanner) and the smoothed, chest wall/mediastinal algorithm (“Standard” on the General Electric scanner).
When obtaining copies of the images, always try to obtain the digital images on a CD, utilizing the DICOM language.
These guidelines above are provided as a public service by Daniel Powers, M.D.: B-Reader and Board Certified Diagnostic Radiologist, Certified by the American Board of Radiology
This article is provided as a public service by Daniel Powers, M.D.: B-Reader and Board-Certified Diagnostic Radiologist, Certified by the American Board of Radiology.
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