Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
1999-06-11
2001-01-16
Manuel, George (Department: 3737)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
Reexamination Certificate
active
06175755
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to methods of analyzing lungs and, more particularly, to methods of estimating the surface area and other parameters of a lung.
BACKGROUND OF THE INVENTION
Emphysema is defined as abnormal permanent enlargement of a lung's airspaces distal to the terminal bronchioles, accompanied by destruction of their walls, without obvious fibrosis. When x rays are applied to a lung, the changes to the lung associated with emphysema decrease the attenuation of x rays passing through the thorax and shift their distribution, allowing advanced emphysema to be detected during life. Not only is it important to be able to detect emphysema during life, it is also important to determine the extent and severity of emphysema during life.
The ability to estimate the extent and severity of emphysema during life is important for several reasons. The accurate detection of lung destruction when it first appears and the careful mapping of its progression over time allow the natural history of emphysema to be better understood. Further, the treatment of advanced emphysema by lung volume reduction surgery requires knowledge of the location of the lesions and an objective method of assessing the surgical result. Finally, recent provocative experimental studies, suggesting that alveolar number and surface area to volume ratio can be restored to a normal level by pharmacotherapy in rats with elastase-induced emphysema (“Retinoic acid treatment abrogates elastase-induced pulmonary emphysema in rats.” Massaro, G. et al.,
Nature Medicine,
3:675-677 (1997)), indicate a future need for measurements that can accurately assess the effectiveness of such therapeutic interventions.
A need exists for methods and apparatus for determining certain parameters of a lung, such as lung surface area, that can be used to diagnose and monitor emphysema progression in a patient, both before and after the patient is surgically and medically treated.
SUMMARY OF THE INVENTION
In accordance with this invention, a computer-implementable method for estimating selected parameters of a lung, such as lung surface area, using computed tomography (CT) is provided. The method combines a quantitative CT scan analysis of a lung with a stereologically based histology quantification of the lung anatomy. In addition to human lungs, the method may be applied to the lungs of other species.
In accordance with further aspects of this invention, a plurality of CT images (slices) containing the image of a lung are obtained from a plurality of subjects. The CT images are sequentially displayed on a screen, such that the intensity of each pixel is determined by its x-ray attenuation value, and analyzed. During analysis, the lung image is extracted from the CT image. After extraction, the method calculates the volume of each lung based on the plurality of lung images extracted from the plurality of CT images, respectively.
The method also calculates a volume-of-gas to weight-of-tissue ratio (inflation value) of each lung. To this end, first the method calculates a volume-of-gas to weight-of-tissue ratio for each pixel included in each of the plurality of lung images, using the x-ray attenuation value of the pixels. The method then obtains a median volume-of-gas to weight-of-tissue ratio for all of the pixels included in all of the lung images.
Next, the method obtains a surface area to volume ratio of each lung using quantitative histology.
After the median volume-of-gas to weight-of-tissue ratio and the surface area to volume ratio for all lungs have been determined, the method plots the surface area to volume ratio versus the median volume-of-gas to weight-of-tissue ratio for the lungs. The method then uses the plot to obtain a best-fit prediction equation that correlates surface area to volume ratio to volume-of-gas to weight-of-tissue ratio.
In accordance with other aspects of this invention, the prediction equation thus obtained is used to estimate the surface area to volume ratio, and the surface area, of a new lung. To this end, at least one CT scan image of the new lung is analyzed in the manner described above to obtain the volume-of-gas to weight-of-tissue ratio of the lung. That is, the lung image is separated from the CT scan image and the x-ray attenuation data and, thus, volume-of-gas to weight-of-tissue ratio associated with each pixel are determined. These data are used to obtain a median volume-of-gas to weight-of-tissue ratio. The method then enters this value into the prediction equation to obtain the surface area to volume ratio of the new lung. The surface area to volume ratio is used to determine the surface area of the lung.
In accordance with further aspects of the present invention, the numerical processing of x-ray attenuation data obtained from a CT scan image to obtain the surface area to volume ratio and the surface area of a lung is carried out by a computer program.
The present method allows a quantitative assessment of a lung to be made without having to remove lung tissue from a patient. Furthermore, as will be readily appreciated by those skilled in this area of technology and others, the present method is much faster and more efficient than lung analysis methods based solely on quantitative histology. The present invention is ideally suited for providing objective quantitative data in meaningful structural and physiologic terms that can be used to follow disease progression and to plan and assess the surgical and medical intervention of the disease.
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Coxson Harvey O.
Hogg James C.
Whittall Kenneth P.
Christensen O'Connor Johnson & Kindness PLLC
Manuel George
The University of British Columbia
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