3.11a. Evaluation of multi-static lung scintigraphy


Examination of pulmonary perfusion and pulmonary ventilation is one of the most common types of scintigraphic diagnostics in nuclear medicine. In addition to the visual evaluation of possible defects in the distribution of the radioindicator on perfusion and ventilation images of the lungs, quantification of relative perfusion or ventilation in the right and left lungs, or as well as regional distribution of function in different lung fields.
Static lung scintigraphy is performed in two variants :

For a more comprehensive assessment of the condition of the lungs, it is useful to perform (sequentially or simultaneously) perfusion and ventilatory scintigraphy.

Evaluation of static lung scintigraphy consists of three stages:

Acquisition of studies

Scintigraphic examination of lung perfusion is performed after iv application of 99m Tc-macroaggregates (human albumin, eg Macro-albumon).

Scintigraphic examination of lung ventilation is performed in two ways:

In addition to separate pulmonary perfusion (with 99m Tc MAA) and separate pulmonary ventilation (with 99m Tc-aerosol, or with 81m Kr gas ), simultaneous combined perfusion + ventilation scintigraphy ( 99m Tc-MAA application and 81m Kr alternating inhalation ) is often performed . All these scintigraphies are further performed in a number of different projections - the basic ones are AP and PA, as well as oblique LPO, RPO, sometimes even lateral LL, RR. The resulting scintigraphic studies then have 2, 4, 6, 8, or 12 images.

Recommended storage mode:

matrix 128 128, 16 bits, preselection min. 200,000 imp./frame, resp. 2min./frame

The basic and always performed projections are the rear projection - Posterior ( PA ) and the front projection - Anterior ( AP ). Quantification of relative pulmonary perfusion and ventilation is also performed on the images of these projections. If necessary, oblique projections are also recorded - DX (RPO), SIN (LPO), or and lateral RL and LL. We recommend the following combination options and projection order:

Separate perfusion or ventilation:
4 screenings:
Picture 1: AP Picture 2: DX Picture 3: SIN Figure 4: PA ----------- -----------
or 6 projections:
1: AP 2: RL 3: RPO 4: LL 5: LPO 6: PA
 
Combined perfusion + ventilation:
4 screenings:
1: AP- perfusion 2: AP -ventilation 3: RPO -perfusion 4: RPO -ventilation    
5: LPO perfusion 6: LPO -ventilation 7: PA perfusion 8: PA -ventilation    
or 6 projections:
1: AP- perfusion 2: AP -ventilation 3: RL perfusion 4: RL -ventilation 5: RPO -perfusion 6: RPO -ventilation
7: LL -perfusion 8: LL -ventilation 9: LPO perfusion 10: LPO -ventilation 11: PA perfusion 12: PA -ventilation

Separated the perfusion scintigraphy and subsequently ventilation:
4 Projection:
1: AP -perfuze 2: RPO -perfuze 3: LPO -perfuze 4: PA -perfuze ,
5: AP -ventilace 6: RPO -ventilace 6: LPO - ventilation, 8: PA -ventilation.

or 6 projections:
1: AP -perfusion , 2: RL -perfusion , 3: RPO -perfusion ,
4: LL -perfusion , 5: LPO -perfusion , 6: PA-perfusion ;
7: AP -ventilation, 8: RL -ventilation, 9: RPO -ventilation,
10: LL -ventilation, 11: LPO -ventilation, 12: PA -ventilation.

These projection sequences correspond to the default presets in the PULMSTAT program, so it is not necessary to permute the projection sequence during evaluation if it is observed.

Evaluation of the study
First we call up the required scintigraphic study in the basic menu PROCESSING. If we want to simultaneously evaluate perfusion and ventilation studies that have been stored separately, we first select a perfusion study and then use the “Next” command to attach a ventilation study to it. We will launch a comprehensive program PULMSTAT - static lung scintigraphy .

Sequence of projections and visual evaluation As mentioned above, there is considerable diversity and variability in the number and order of individual projections of perfusion and ventilation images in multistatic lung scintigraphy. Therefore, there may be a problem with correctly assigning projections . This problem is solved in the PULMSTAT program in two stages. Stage 1: After starting the program, a preview of all stored images in the original order is displayed first (Fig.3.11a.1).


Fig.3.11a.1. 1st stage of assignment of projections - according to the preview of images we specify the type of study and the number of projections.

At the request of the program, we first specify which lung scintigraphy it is - whether it is a perfusion , ventilation study , or a combined perfusion + ventilation study. Next, we specify the number of projections used.

Fig.3.11a.2. In the images of the default projection assignment, we can decide whether the assignment is correct.

Based on this specification, the program will make the appropriate assignment and the display will show the accumulated lung images and describe the names of the projections in the default order, eg Anterior - RPO - LPO - Posterior - DX - SIN (only as many projections as the images stored ) - fig.3.11a.2. If the projection order agrees and we want to keep all the images, we will answer the program question "Projection order okay?" positive.
Stage 2:
Otherwise (negative answer) an image template with default projection names will be displayed, on which we will gradually
move the images with the mouseso as to achieve the correct assignment of images to the names of projections - Fig.3.11a.3. In this way, it is possible not only to change the order of projections, but also to select certain images and reject others for further display, processing and documentation. This 2nd stage allows you to select the correct assignment of projections even in cases where none of the recommended order of saving projections was observed or when errors occurred during storage.

Fig.3.11a.3. 2nd stage of assignment of projections - individual images can be flexibly moved with the mouse to the corresponding frames of the template.

If we have displayed images with the corresponding assignment of projections, a visual evaluation begins , and we can use both the implicit standard formulation of the normal evaluation, eg for perfusion:

When evaluating scintigraphic images of lung perfusion in all projections,
we observe a homogeneous distribution of the radioindicator in both lung wings
- without a defect.

Conclusion:
Normal perfusion scintigram of the lungs.

resp. for ventilation:

When evaluating scintigraphic images of lung ventilation in all projections,
we observe a homogeneous distribution of the radioindicator in both lung wings
- without a defect.

Conclusion:
Normal ventilatory lung scintigram.

or a non-standard or free text of a pathological finding.

Quantifying relative perfusion or ventilation
To quantify relative perfusion or ventilation, the display first shows the lungs in the posterior projection, indicating the left and right lungs. Follow the instructions on the screen to mark the areas of interest (Fig.3.11a.4):

The background is best located in the area between the two lungs and below them. We implicitly use irregular regions of interest (IR), but we can also use quadrangular (RI). After finishing the definition of ROI on the rear projection, we mark the ROI of the lungs and the background in the image of the front projection in the same way. Pay attention to the order - in the front projection we start with ROI 1 of the left lung on the right side of the image!

Fig.3.11a.4. Quantification of relative ventilation of the left and right lungs.

After the ROI marking is completed, the actual calculation of relative perfusion or ventilation is performed . For both images are integrated ROI left and right lung is subtracted background, using geometric mean integrals themselves respective parts of the lungs in the front and back projection is performed correction for differences in absorption of gamma *) and calculates the relative position of each lung percentages global function of both lung. We have the option of either agreeing the calculation or repeating it for the same or different projections, with or without correction for absorption. Furthermore, it is possible to determine relative perfusion and ventilation and regions for each arbitrary part of the lungs as defined by the ROI.
*) The method of correction for different absorption of gamma radiation from the left and right lungs is analogous to that of static scintigraphy of the kidneys - see chapter 3.7.

Final protocol
The display shows all preset lung projections along with the result of determining relative perfusion or ventilation. In the box below we can edit the text of the verbal description of the scintigraphic images and the conclusion. Finally, we can
print a report containing (in addition to basic data such as the patient's name) the relevant images, the results of the determination of relative perfusion or ventilation and the text of the verbal evaluation, conclusion and signature - Fig. 3.11a.5.

Department of Nuclear Medicine,  University Hospital  Ostrava                   Date: ..............
Name of patient: ....................... .                   Birth certificate number: .........................
Computer evaluation of multistatic scintigraphy of combined pulmonary perfusion and ventilation
Visual evaluation:
When evaluating scintigraphic images of lung ventilation in all projections, we observe a homogeneous distribution of the radioindicator in both lung wings - without a defect .
On scintigraphic images of lung perfusion, we observe an inhomogeneous distribution of the radioindicator in both lung wings with several areas of hypoperfusion, without segmental defects

Conclusion:
Normal ventilation scintigrams of the lungs, several areas of hypoperfusion in both lung wings.
Practically symmetrical relative perfusion and ventilation of the left and right lungs.
Compared to the examination from 10.5. tr significant regression of pulmonary disorders is evident.
                                                                                       
Signature: MUDr. O. Kraft

Fig.3.11a.5. Example of a result protocol for the evaluation of multistatic scintigraphy of pulmonary perfusion and ventilation.
Dynamic liver scintigraphy   Dynamic scintigraphy of pulmonary ventilation

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