Model of Kr81m Admin.

 

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A simple mathematical model of ventilation (in EXCEL) was used to evaluate the Kr81m activity in the lungs during a ventilation study. This model can demonstrate the pattern of activity in the lungs (using the reservoir system) with a normal breathing pattern, the effect of breathing deeply and also the effect of having no reservoir system .

Model parameters
the lungs are a single miscible compartment
breathing is at a steady flow
each breath is 4s
normal tidal breathing is 10% of lung volume
deep breathing is 20% of lung volume
the areas under each graph are identical up to the point of the end of the study
the generator strength is 300MBq effective activity
decay is calculated continuously

 

Normal Breathing Pattern

The initial level of activity is due to the spike of activity at the moment of switch on of the generator.  The approximate level of activity in the lungs during the study   is equivalent to about 100MBq. The study is assumed to be 80s and then the generator is switched off and the lung activity drops quickly due to both breathing out and decay.

 kr_norm.gif (3717 bytes)

 

 Deep Breathing Pattern

The initial level of activity is the same as with normal breathing pattern. However this rapidly reaches a lower running average of about 70MBq. This is due to the greater activity loss during breathing out, whereas there is no increase in activity being delivered. The scan therefore takes longer (108s compared to 80s).

dpbreath.gif (3492 bytes)

 

 No Reservoir System

If no reservoir system is used then it is possible that the initial spike of activity may be lost. There is also no storage of Kr81m activity while the patient is breathing out. The running average of the lung activity is about 50MBq. The scan takes 175s instead of 80s .

kr_no_bolus.gif (3661 bytes)

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Last modified: November 29, 2002