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Clinical Practice Keywords Lungs/Air flow/Pregnancy/ Blood /Pulmonary emboli Review This article has been double-blind peer reviewed In this article... ● Principle of ventilation/perfusion ● How ventilation/perfusion imaging is used to diagnose pulmonary emboli ● Precautions required when patients undergo ventilation/perfusion imaging

Nuclear medicine 5: ventilation/ perfusion scintigraphy

Key points Authors Joseph Purden and Faye Morton are lecturers in medical physics technology, Ventilation/perfusion College of Human and Health Sciences, Swansea University. scintigraphy is used to assess air flow Abstract Nuclear medicine provides imaging modalities that can be used to observe and blood perfusion physiological processes in the human body, particularly in the bones, heart, lungs, in the lungs renal system and brain. Ventilation/perfusion scintigraphy is used to assess air flow and blood perfusion in the lungs and is, therefore, indicated when pulmonary emboli The technique are suspected, particularly in women who are pregnant. This final article in a five-part requires the use of series explains how ventilation/perfusion imaging works and what precautions need both an inhaled to be taken with, and around, patients undergoing this investigation. and an injected radioactive drug Citation Purden J, Morton F (2019) Nuclear medicine 5: ventilation/perfusion scintigraphy. Nursing Times [online]; 115: 7, 61-62. It is mostly used to detect or confirm pulmonary emboli entilation/perfusion (V/Q) scin- taken at various angles. Ventilation images tigraphy is a diagnostic investi- are often acquired before perfusion images This type of imaging gation used in nuclear medi- but, if using a radioactive gas, both types of is used in pregnant Vcine to evaluate air flow (V) and images can be acquired at the same time. women in particular, blood perfusion (Q) in the lungs. It is most due to the lower commonly used to detect or confirm pul- Second phase radiation burden monary emboli (blood clots lodged in the In the second phase, while the patient is compared with capillaries, which cause blockages that still supine, a perfusion radiopharmaceu- other investigations restrict blood flow to some areas of the tical is administered intravenously and lung). lodges in the capillary beds. It cannot The risks to travel past blood clots occluding the ves- pregnant women How does it work? sels so, if there are areas that have taken up and their unborn In V/Q scintigraphy, as explained by Gray smaller amounts of radioactivity (or none babies are small, (2005), images are acquired in two phases: at all), this indicates a high likelihood of but patients need l After inhalation of a radioactive gas to pulmonary emboli. to be made fully assess ventilation of the airways; Imaging takes place straight after the aware of them l After intravenous administration of a injection of the radiopharmaceutical and radioactive colloid to assess perfusion of usually takes 5-20 minutes, depending on blood in the capillary beds of the lungs. factors such as the activity of the chosen radiopharmaceutical. Perfusion images First phase need to be taken from the same angles as The test begins with the administration of ventilation images, so the two sets can be a ventilation radiopharmaceutical, which accurately compared. can be in the form of a nebulised agent If the perfusion radiopharmaceutical is (inhaled into the lungs through a nebu- not properly mixed before it is injected, liser) or a gas (inhaled into the lungs there may be a clumping of particles that through a mask or mouthpiece). Images could cause an artefact (see part 2). This showing the air supply to the lungs are can sometimes result in images that are

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not usable for diagnostic purposes. Fig 1. Ventilation and Patients should not have close contact Clumping artefacts are commonly perfusion imaging with young children or pregnant women – observed in ventilation images acquired the two groups who are most at risk from using the radioisotope technetium-99m radiation – for 24 hours after administra- (99mTc) (see part 1) combined with the tion of the radiopharmaceutical. Ideally, chelating agent diethylenetriaminepenta- staff members who are pregnant should acetic acid (DTPA). They are more likely to not care for patients who have just had V/Q be present in patients with chronic imaging, and all staff need to take extra obstructive pulmonary disease (COPD) care to reduce their own exposure to radia- (Ziessman et al, 2013). tion. After 24 hours, standard staff rotas Central lines should be avoided when and care protocols can be resumed. injecting the radiopharmaceutical, as it may not have time to adequately mix with Conclusion the blood in the pulmonary artery before Legislation surrounding radiation protec- reaching the lungs, which would cause tion states the importance of keeping radi- poor distribution (Parker et al, 2012). ation exposure of staff and patients as low Another necessary precaution is to avoid 1 in 280,000 as is reasonably achievable. Nursing staff drawing blood back into the syringe and QUICK Children who develop should ensure they keep their distance re-injecting it, as this may cause hot spots FACT cancer after their mothers from patients who have recently under- on the images. undergo V/Q imaging gone a nuclear medicine procedure, and staff should ensure pregnant women and Comparing the images consent is often required before adminis- children keep their distance from the The two sets of images are compared. If the tration to ensure she is aware of the risks to patient for 24 hours post investigation. ventilation images (first set) do not show herself and the foetus (International Com- It is also important to reduce the time anything abnormal but the perfusion mission on Radiological Protection, 2000). spent in close proximity with these images (second set) do, this suggests pul- Pregnant women can undergo V/Q patients wherever feasible – for example, monary embolism. Defects that are indica- imaging relatively safely. The risk of the taking samples of blood, urine or faeces tive of are called future baby developing cancer in child- should be avoided if possible. The han- ‘segmental’, referring to the anatomical hood after the mother has undergone a V/Q dling of any of these fluids should be segments of the lungs each supplied with a scan is very low; it sits at approximately 1 in undertaken with care, and with the use of separate arterial branch; they often have a 280,000 people (Cook and Kyriou, 2005). gloves and aprons. If there are any queries triangular shape (Fig 1). If ventilation and about specific nuclear medicine patient perfusion images contain matching Radiation protection care, the local nuclear medicine depart- abnormal defects distributed in a patchy Women who are breastfeeding can safely ment or medical physics expert can offer pattern, this is indicative of COPD. undergo V/Q imaging. However, they advice. NT should express and discard their breast “Legislation surrounding milk for 12 hours after intravenous injec- References tion of the radiopharmaceutical, as it will Cook JV, Kyriou J (2005) Radiation from CT and radiation protection states perfusion scanning in pregnancy. British Medical contain levels of radiation that are higher Journal; 331: 7512, 350. the importance of keeping than normal (ICRP, 2000). Gray HW (2005) The lung. In: Sharp PF et al (eds) radiation exposure of staff After V/Q imaging, patients should be (2005) Practical Nuclear Medicine. London: encouraged to drink plenty and urinate Springer Verlag. and patients as low as is International Commission on Radiological often, unless contraindicated. This will reasonably achievable” Protection (2000) Pregnancy and medical help them clear the radioactive drug radiation. Annals of the ICRP: Publication 84; 30: 1. (which is excreted via the urinary tract) Parker JA et al (2012) SNM practice guideline for Preparing patients from their system more quickly and, for lung scintigraphy 4.0. Journal of Nuclear Medicine V/Q imaging is commonly used to investi- those who are pregnant, help reduce the Technology; 40: 1, 57-65. Ziessman H et al (2013) Nuclear Medicine: The gate potential pulmonary embolism in dose of radiation received by the foetus Requisites. Philadelphia, PA: Elsevier Saunders. patients who are pregnant due to the lower because of concentration of radioactive

radiation burden, compared with other urine in the patient’s bladder (ICRP, 2000). CLINICAL investigation methods. Due to the nature If samples of blood, urine or faeces need SERIES Nuclear medicine series of ionising radiation, pregnant women are to be collected from a patient in the Part 1: Technique, indications Mar often anxious about the dose of radiation 24 hours after V/Q imaging, nurses should and the nurse’s role the foetus might receive. take extra care and: Bit.ly/NTNuclear1 Patients undergoing nuclear medicine l Wear gloves, an apron and shoe Part 2: Bone scintigraphy Apr investigations sometimes assume radia- coverings; Bit.ly/NTNuclear2 tion begins with the imaging process. This l Use absorbent pads to clean up any Part 3: Myocardial perfusion imaging May is not the case: radiation starts with the spillages. Bit.ly/NTNuclear3 administration of the radiopharmaceu- If possible, it is advisable to either per- Part 4: ventriculography Jun tical. This should be very clearly explained form sample collection before the injec- Bit.ly/NTNuclear4 to the patient before administration. If the tion of the radioactive drug or postpone it Part 5: Ventilation/perfusion scintigraphy Jul

SPL patient is a pregnant woman, written until after 24 hours after the investigation.

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