European Nuclear Medicine Guide
The regional ventilation distribution can be assessed with a ventilation scintigraphy after inhalation of a radioactive aerosol or gas. Krypton-81m is an inert radioactive gas that is delivered from a rubidium-81/krypton-81m generator. Krypton-81m has a short half-life (13 s) and is inhaled continuously during ventilation imaging. The gas disappears from the alveolar regions by decay faster than expiration. Thus, the regional krypton-81m concentration reflects true regional ventilation at normal breath-rate.
General indications for lung ventilation scintigraphy with krypton-81m often combined with a perfusion scintigraphy include, but are not limited to:
General indications for lung ventilation scintigraphy with Krypton-81m often combined with a perfusion scintigraphy include, but are not limited to:
Regarding the ventilation study, it is not recommended to interrupt breast feeding [3,91].
Krypton-81m is used as part of ventilation studies either performed as planar or SPECT, and the most frequent indication is diagnosis of PE. A normal perfusion scan excludes PE, and a ventilation scan is not needed. However, if the perfusion scan is abnormal, a ventilation scan is needed for the interpretation. So, in many cases V/Q scintigraphy is performed. Regarding the clinical performance of V/Q scintigraphy see details under the 99mTc-MAA perfusion scintigraphy. Due to the different gamma energy of krypton-81m and technetium-99m, it is possible to acquire the V/Q scan (with krypton-81m/99mTc-MAA) simultaneously. Sequential V and Q imaging is also possible.
A krypton-81m ventilation scan without a perfusion scan can be used to evaluate ventilation inhomogeneity, as often seen in obstructive lung disease, and can be used for regional lung function evaluation.
The organ receiving the largest radiation dose is the lung (210 nGy/MBq). The ED equivalent is 27 nSv/MBq. (Reference activity 6 GBq ~ 0.16 mSv).
Caveat
“Effective Dose” is a protection quantity that provides a dose value related to the probability of health detriment to an adult reference person due to stochastic effects from exposure to low doses of ionizing radiation. It should not be used to quantify the radiation risk for a single individual associated with a particular nuclear medicine examination. It is used to characterize a certain examination in comparison to alternatives, but it should be emphasized that if the actual risk to a certain patient population is to be assessed, it is mandatory to apply risk factors (per mSv) that are appropriate for the gender, the age distribution and the disease state of that population."
For interpretation of combined V/Q scintigraphy, the reader is referred to the chapter on 99mTc-MAA perfusion scintigraphy.
Ventilation defects often occur in moderate to severe COPD, asthma, cystic fibrosis, lung fibrosis, atelectasis, lung tumour, pneumonia, pleural effusion, and pulmonary infarction.
Pitfalls include that the krypton-81m gas distribution might not reflect true regional ventilation if steady state does not occur due to very fast breathing during gas inhalation.
The cyclotron produced rubidium-81/krypton-81m generator has a short T1/2 of 4.6 h, and this limits availability.
No particular patient preparation is needed before 81mKr lung ventilation scintigraphy.
A recent standard chest radiograph or a CT scan can help in the interpretation. However, this is not needed if a CT scan is performed as part of a SPECT/CT procedure.
The detailed recommendations are available in the EANM Pulmonary Embolism Guidelines. Further information can be found in the published literature [93].