3.11b. Dynamic scintigraphy of pulmonary ventilation
Dynamic scintigraphy of pulmonary ventilation is a comprehensive examination that allows detailed and regional quantification of a number of parameters of lung respiratory function - total lung capacity, residual volume, exchange fraction of air in the alveoli (per unit lung volume) and exchange volume of air.
Dynamic scintigraphic examination of pulmonary ventilation is performed using a special spirometric breathing apparatus allowing to breathe in a closed circuit a mixture of air and radioactive gas xenon 133 Xe - thus breathing air "marked" 133 Xe. The patient, sitting with his back resting on the camera detector, first breathes a mixture of air and 133 Xe in a closed circuit for a few minutes so as to establish an equilibrium concentration.radioactive gas (equilibrium) is lubricated by the lung chambers and the working space of the respiratory system; it takes about 3 minutes. The camera is set so that both lungs are in the field of view and dynamic acquisition is started - frame rate approx. 5sec./frame. The patient then - still in the equilibrium stage - performs the maximum inhale and exhalation several times (at least 2 times) with breath holding, while the corresponding volume differences are read on the respiratory system. This spirometrically measured difference in volumes between max. Inspiration and expiration will be used for quantitative (absolute - "volume-pulse") calibration of scintigraphic data
in the evaluation . Then the appropriate valve is opened and the patient breathes normal air without radioxenone, thereby radioactive 133Xe gradually exhales from the lungs. The rate of disappearance of 133 Xe from the lungs, the so-called wash-out , is one of the important measures of the performance of this organ - pulmonary ventilation . The accumulation of dynamic scintigraphy ends when practically no 133 Xe (body background level) remain in the lungs - this is usually after 5-8 minutes from the start of the wash-out.
significant phases of ventilation
In the computer evaluation of the dynamic study thus obtained, the areas of interest (ROI) of the left lung, right lung and tissue background are first marked on the summation image of the equilibrium (Fig ... a). From these areas, curves of the time course of radioactivity 133 Xe during the examination are formed . The curve from the lungs has a typical shape (Fig.3.11b.1 top left): at the beginning of the equilibrium , where the elevated points corresponding to the maximum inspiration and the decreased points corresponding to the maximum expiration are visible; followed by a phase of exhalation 133 Xe from the lungs (wash-out) in which the activity of the lungs decreases gradually to the level of body background.
|Fig.3.11b.1. Principle of absolute dynamic scintigraphy of the lungs by breathing 133 Xe in a closed circuit (max. Inspiration and expiration, equilibrium) and subsequently in an open circuit (wash-out).|
The points and sections corresponding to the maximum inhale and exhale, equilibrium and the wash-out section are then defined on this curve (automatically with the possibility of manual intervention). By summing the images corresponding to these dynamically significant points and sections, the resulting scintigraphic images of the characteristic stages of the examination are created, and further analysis is used to construct parametric images and calculate the values ??of quantitative parameters.
Parametric images of
the regional distribution of spirometric parameters
Images corresponding to significant points and sections defined on the time course curve of radioactivity 133 Xe in the lungs are summed , thus creating images of the lungs in the phase of max. Inspiration, max. 2 c, d, e).
|Fig.3.11b.2. Mathematical analysis of
dynamic scintigraphy of pulmonary ventilation.
a) Areas of interest of the left and right lungs and background. b) Time course curves of radioactivity 133 Xe in the lungs and background. c) Equilibrium image. d) Image of lungs in max. breath (TLC distribution). e) Image of max. exhalation (residue distribution). f) Parametric picture of vital capacity. g) Parametric picture of the distribution of effective ventilation (exchange volume). h) Parametric picture of the regional distribution of the exchangeable air fraction.
Next, we enter the
measured value of the volume
between the maximum inhale and exhalation (in milliliters). Based
on this value and the difference between the charged number of
pulses in the respective images of the lung max. Inpiriu and
expirium calculated calibration
factor F between nastřádanám number of pulses
and the volume of air (the "tagged" 133 Xe) in milliliters - scintigraphic
studies thus becomes quantitative and what the absolute volumes - each impulse in each element of the
image is expressed in milliliters
of air at a
given location of the lungs.
The program then creates images of the distribution of pulmonary volume in equilibrium, the distribution of vital capacity of the lungs at maximum inspiration, the distribution of residual volume at maximum expiration and the distribution of vital capacity of the lungs - Fig.3.11b.2 c, d, e, f. These images are quantified - the contents of individual cells directly indicate the number of milliliters of air at a given site of the lung - they are locally parametric images.
Then follows the construction of locally parametric images of the regional distribution of pulmonary ventilation . A time course curve of radioactivity 133 is generated for each point in the image matrixXe at this point and from it the relevant ventilation quantity is calculated according to the formulas in the lower part of Fig.4.11b.1 - exchangeable fraction EF [% / s] and exchangeable volume EV [ml./s], ie the amount of air that is in replace at the appropriate location in 1 second. The parameter calculated in this way is then stored at the point in the image from which the analyzed curve originated. This is done for all points of the image matrix, which gives parametric or functional images , which is a kind of clear "map" of the regional distribution of the dynamics of the studied process - pulmonary ventilation (Fig.3.11b.2 g, h):
From these parametric images it is clear which parts of the lungs have better or worse functional (respiratory) ability and it is also possible to immediately determine the local values ??of the relevant quantitative ventilation parameters at each location - exchange air fraction in percent and exchange volume in milliliters per second .
|Fig.3.11b.3. Regional distribution of exchange fraction in individual lung fields.|
The regional distribution of lung ventilation parameters is sometimes evaluated for individual lung segments . The areas of interest of the left and right lungs are usually divided vertically into three equally large parts, in which the average or summary values ??of the required ventilation parameters are calculated from parametric images and also expressed as a percentage of the total global value - an example is shown in Fig.3.11b .3.
|Nuclear physics and physics of ionizing radiation | OSTNUCLINE|
|Nuclear and radiation physics||Radiation detection and spectrometry||Radiation applications|
|With cintigraphy||Computer evaluation of scintigraphy||Radiation protection|
|Gravity, black holes and space - time physics Anthropic principle or cosmic God|
|AstroNuclPhysics ® Nuclear Physics - Astrophysics - Cosmology - Philosophy|