Lung imaging measurements

In vivo imaging can provide detail suitable for lung volume measurements and may provide detail suitable for lung density measurements. 

Surprisingly the first attempts to measure displacements originating from genuine periodic or quasi-periodic perturbations were carried out in vivo. Those studies took advantage of the internal pulsatile motions provided by heart beating. As soon as 1982 small displacements from aortic pulsations were visualized in liver on M-mode scans.69 It was shown that such displacements could be calculated from correlated successive A-scans,70 with an application on liver.71,72 Correlation techniques were also applied on M-mode images to quantitatively estimate motions and deformations of fetal lung.73,74... 

To measure lung deposition by imaging, the aerosol must be first labelled or tagged with a suitable radionuclide. Radiolabelling techniques have been developed for current inhalation products including nebulizers, propellant-driven metered dose inhalers, and dry powder inhalers. 

Computerised tomography (CT) images can be enhanced by inhaled xenon and 133Xe has been widely used to measure regional cerebral blood flow. Several studies have shown increases in cerebral blood flow during xenon inhalation in both volunteers and patients with head injury. Xenon anaesthesia is probably unsuitable in the presence of intracranial disease. Xenon-enhanced CT scanning is said to be safe, provided the lungs are hyperventilated to prevent an increase in intracranial pressure. 

A subsequent investigation (6 ) studied the resolution and sensitivity of Mn-52m as a quantitative measurement of the size and location of myocardial ischemia. Comparison between microsphere distributions and Mn-52m images taken at 1.5 cm levels revealed that an ischemic area down to the size of 2.5 cm with 50% of the normal myocardial perfusion can be seen in the positron images. In addition, a relative change of 10% or more of the normal perfusion in the ischemic area can also be observed. Large clinical studies with the Fe-52m/Mn-52m generator have recently been initiated at the National Heart and Lung and Institute, National Institutes of Health, Bethesda, Maryland ... 

Fleming, J.S. Conway, J.H. Holgate, S.T. Moore, E.A. Hashish, A.H. Bailey, A.G. Martonen, T.B. Evaluation of the accuracy and precision of lung aerosol deposition measurements from planar radionuclide imaging using simulation. Phys. Med. Biol. 1998, 43, 2423-2429. 

When imaging a subject after inhalation of a radiolabeled formulation, it is the radioactivity that is detected and measured absolute amounts of deposited drug are inferred from the counts of radioactivity in the lung and other regions, based on the assumption that there is a 1 1 relationship between the two components. This relationship holds true for direct-labeled PET products or for those formulations where a firm bond can be demonstrated between the drug and radioactivity for the time taken to acquire all the images. 

Using planar imaging, expressing the dose deposited in the lung in absolute terms requires the measurement of global lung tissue attenuation factors... 

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