Lung Ventilation-Perfusion Scintigraphy
Procedural Guidelines for Lung Perfusion & Ventilation scintigraphy

Lung Perfusion:
Patient preparation:
1. Most of the times this procedure is done as an emergency one.
2. No special preparation needed
3. Ensure that patient does not have any known allergy to any protein substances.
4. It is very important to document presence of right to left cardiac shunt, severe lung AV malformations, before injection of MAA particles as there is a risk of precipitating systemic circulation embolism (infarcts of brain, kidneys) in this patient.
5. It is also important to document the presence of severe pulmonary hypertension

Preparation of 99mTc MAA:
Precautions:
1. It is essential to know the no. of MAA particles in a particular vial (no. of particles can differ according to the manufacturer) so that the desired number of particles & radioactivity can be dispensed.
2. Normally it is preferred to inject 2 - 5 lakhs particles per patient. Reduced numbers of MAA particles should be considered for patients with severe pulmonary hypertension or right-to left shunting and in children. Minimum injected MAA should be not less than 60,000 – 1,00,000 particles.
3. Volume of pertechnetate added to MAA vial should be such that, when 3 – 4 mCi of 99mTc MAA dispensed it should not contain more than 2 – 5 lakhs particles.
4. Labeled MAA particles will settle at the bottom of vial with time. Vials should be agitated prior to withdrawing a dose, and the syringe should be inverted prior to injection.

Injection of 99mTc MAA:
1. While injecting Tc MAA intravenously into the patient never draw out blood into the syringe as it causes “Hot spots” in the lungs and scan becomes uninterruptible.
2. The MAA injection should not be given through an indwelling catheter that is not well flushed. A direct IV injection of MAA is always preferred.
3. Always inject Tc MAA very slowly into the patient as it can cause allergic reaction in some patients.
4. Supine position is advised during injection & patient should be instructed to inhale deeply during injection.

Lung Ventilation:
Patient preparation:
No special preparation needed
Patient should be explained the aerosol inhalation procedure as active normal inhalation is an important prerequisite for a good ventilation study
A “mock inhalation” of oxygen should precede the radioactive aerosol inhalation.

Radio Pharmaceutical:
Normally 25mCi of 99mTc DTPA or phytate in a volume of 2-3 ml is added into aerosol swirler unit.

Procedure:
1. Patient should inhale aerosol preferably in sitting position or in supine.
2. Patient should inhale aerosol atleast for 3-4 minutes
3. Patient should not hyperventilate. Rather patient should be instructed to inhale & exhale normally
4. Radiation safety measures should be strictly followed during the aerosol generation & administration to patient.

Protocols:
Same day Ventilation & Perfusion Imaging:
Ventilation scintigraphy using 99mTc DTPA is usually performed before perfusion scintigraphy using 99mTc-99m MAA especially in patients where there is a high suspicion of pulmonary embolism.

Separate day Procedure:
Alternately, a perfusion scintigraphy can be performed first and ventilation scintigraphy omitted if there are no perfusion defects. If the perfusion study is abnormal then ventilation study should be performed only after 24 hours.

Image Acquisition:
1. Planar images, (using a 128 X 128 matrix, LEAP / High Resolution parallel hole collimator) should be obtained in multiple projections (anterior, posterior, Right & left posterior oblique & both lateral).
2. In some patients it may be possible to obtain only limited views.
3. If a MAA perfusion imaging is done immediately after a ventilation study then it should be ensured that the count rate after 99mTc MAA injection is at least 5 times than that of ventilation images.

Image Processing:
No special processing is needed if imaging is done for pulmonary embolism.
If imaging is done for postoperative prediction of FEV1 or to assess the pulmonary artery patency then percentage distribution of MAA / aerosol in both lungs by geometric mean method is to be calculated.

Image Display :
Savescreen prints have to be formatted with threshold and background adjusted according to the scan interpretation i.e. if perfusion defects are there it should be shown on the print.
All the acquired images are to be formatted as lung ventilation and perfusion images in the same order i.e. anterior, posterior, LPO etc for easier comparison.