Radionuclide Pulmonary
imaging
(LUNG V/Q SCAN)
Radiology Resident Half Academic Day
Dr Hussein Farghaly
Nuclear Medicine Consultant
PSMMC
Riyadh, KSA March, 2011
Clinical Application:
•
A. The most common clinical indication for lung scintigraphy is to determine the likelihood of
pulmonary embolism (PE).
•
B. Less common clinical indications are:
1. Document the degree of resolution of pulmonary embolism
2. Quantify differential pulmonary function before pulmonary surgery for lung cancer
3. Evaluate lung transplants
4. Evaluate congenital heart or lung disease such as cardiac shunts, pulmonary arterial stenosis,
and arteriovenous fistulae and their treatment
5. Confirm the presence of bronchopleural fistula
6. Evaluate chronic pulmonary parenchymal disorders such as cystic fibrosis
7. Evaluate the cause of pulmonary hypertension
PROCEDURE/SPECIFICATIONS OF THE EXAMINATION
• Nuclear Medicine study request:
-Women of childbearing age
-Clinical pre test probability of PE (Wells score)
-D-Dimer test
-History of prior DVT or PE or anticoagulant therapy
-Review of prior lung scintigraphy
-Relevant chest radiographic findings
• Patient Preparation and Precautions
-A standard chest X-ray CT scan can substitute
- Pregnant or breastfeeding women: benefit versus risk.
- Discontinue breastfeeding for 24 hours
- Children < 3 years of age: Limit close contact for 24 hours.
Perfusion scan: Agent:
• Tc-99m macro-aggregated albumin (Tc-99m MAA)
• Particle size: 10-90 microns (90% of particles)
• No particles should be larger than 150 microns
• Obstructing ~ 0.1% of precapillary arterioles
• Particles clearance: Enzymatic hydrolysis and phagocytized by
reticuloendothelial cells (biologic half-life of 6-8 hours).
• Critical organ: Lungs, 1 rad/5 mCi Total RDE : ~ 0.8 mSv
Perfusion scan: Agent cont.:
Number of particles: 500,000 particles/5mCi, Minimum of 70,000
Reduced number of particles:
100,000 in Pulmonary arterial hypertension (> 50 mmHg), right to left shunts,
status post pneumonectomy, poor respiratory function, cardiopulmonary
instability.
10,000 to 50,000 particles in Neonates:
• Neonate have about 10% of adult pulmonary capillaries
• Number of capillaries increases to half of the adult value by age 3 years,
and reaches an adult level by age 8 to 12 years.
• Dose and adminstraion: Adult 40–150 MBq (1–4 mCi).
Pediatric 1.11 MBq/kg (0.03 mCi/kg) with a minimum of 14.8 MBq/kg (0.4
mCi)
- Tc-99m MAA is injected IV slowly during 3–5 respiratory cycles with the
patient in the supine position..
-
Perfusion scan: Imaging
• Imaging is preferably performed in the upright position to increase chest cavity
size and to minimize diaphragmatic motion.
• Large field of view camera, parallel hole and high-resolution collimator. Planar
images should be obtained in multiple projections including anterior, posterior,
both posterior oblique, both anterior oblique and both lateral projections
•
SPECT can be used to obtain a three-dimensional evaluation of the perfusion,
and is recommended by some investigators.
•
Images of the brain may be obtained to distinguish right-to-left shunting from
systemic distribution of radiopharmaceutical components too small to be
trapped by capillaries.
• Tc-99m MAA injection into the veins of the feet: May help to reveal a DVT as
"hot spots" Venous obstruction or collateral flow can be seen
Tc-99m MAA Perfusion Lung Scan
Ventilation scan: Radiopharmaceuticals
RADIOACTIVE GASES:
- Xenon-133 (5 days, 81KeV )
- Krypton-81m (13 sec, 190 KeV, RU-81/Kr-81m generator)
RADIOAEROSOL:
-Technegas “pseudo-gas (0.005–0.2 μm)
-Tc-99m DTPA aerosol (0.1–0.5 μm)
Ventilation scan: Xenon-133
•
•
•
•
•
•
•
•
Gamma energy: 81 keV
Physical half-life: 5.2 days
Dose inhaled: 15-25 mCi through Xenon delivery device.
Critical organs: Trachea and airways of ~ 250 mrad
Absorbed dose by the body: Less than 15%
Total radiation dose equivalent: 1.2 -2.0 mSv
Xe-133 ventilation scan performed prior to Q scan
Uncommon practice: Xe-133 exam after the perfusion study;
low dose of Tc-99m MAA first (1-2 mCi) and then high dose of
Xe-133 (20-30 mCi)
Ventilation scan: Xenon-133
•
•
Gamma camera placed behind the patient's back: Posterior view.
Xe-133 is inhaled through a mouthpiece of the Xenon delivery system.
Ventilation scan in 3 phases:
• Single breath: At maximum inspiration take 10-15 sec image. COPD detected in
~ 66%
• Equilibrium: Normal tidal respirations for 3-5 minutes, rebreathing a mixture
of Xenon-133 and oxygen take two sequential 90 sec images. Least sensitive
for COPD diagnosis.
• Washout: Patient breaths room air or oxygen while exhaling the xenon into a
charcoal trap take three sequential 45 sec images. Biological half life is 30 sec.
• Normal Xenon-133 clearance: 2-3 minutes. Clearance > 3 minutes: Air
trapping. More sensitive (90%) than single breath phase in diagnosing COPD.
• Xenon more sensitive than aerosolized Tc-DTPA for detecting COPD.
Xenon ventilation scan
Ventilation scan: Krypton-81m
•
•
•
•
Rubidium krypton-81m generator.
Isomeric transition like Tc-99m
Gamma emission: 191 keV (65%)
Physical half-life: 13 seconds

•
•
•
Advantages:
Higher energy than Tc-99m
Very short physical half-life: V imaging immediately after each Q image
Radiation dose to the lungs is lower than with other agents (about 15 mrad
per view).
 Disadvantages:
• Rubidium 81m: Physical half-life ~ 4.5 hours, can be used only for 1 day
• Limited assessment of COPD because tracer decays before an equilibrium
distribution can be attained
Ventilation scan: Tc-99m DTPA
• Submicronic particles (aerosols) inhaled through an aerosol
delivery system.
• Particles size: 0.5 to 0.8 microns in diameter, reaching alveoli
• Dose: 30 mCi (3-5 minutes rebreathing within closed system,
oxygen at 8-10 liters/min).
• System delivers about 0.5-0.8 mCi of tracer to the lungs
100,000 counts images in about 2-5 minutes.
• Radiation exposure to the lungs: ~ 100 mrads.
• Exposure to personnel: Less compared with Xenon study.
• Half-time clearance: 1-1.5 hours in normal patients; more
rapid clearance in patients with PE, lung injury (ARDS),
pulmonary fibrosis, and in smokers (20 min.)
Tc-99m DTPA vs. Xe-133
Advantages of Tc-99m DTPA :
• No collection devices for exhaled gas
• Multiple projections
• Can perform before or after perfusion scan
• Feasible for ICU patients on ventilator
Disadvantage of Tc-99m DTPA :
• Air trapping cannot be assessed.
• Xenon more sensitive than Tc-DTPA for
detecting COPD.
Ventilation scan: Tc-99m technegas
• Tc-04 is vaporized in a microfurnace: Ultrafine labelled carbon
particles.
• Particle size: 0.05 and 0.15 microns
• Good peripheral deposition: even in COPD.
• Longer pulmonary retention no effective clearance half time
is 6hrs
• The material is produced by heating 5mCi
of Tc- pertechnetate to very high temperatures
(2500 degrees Celsius) in the presence of
100% argon gas produced a Tc-carbon
particle that is so small it acts like a gas.
Image Sequence:
• A. A chest radiograph should be obtained and reviewed before lung
scintigraphy.
• B. Ventilation scintigraphy using 133Xe is usually performed before
perfusion scintigraphy. Alternately, perfusion scintigraphy can be
performed first and ventilation scintigraphy omitted if not needed.
• C. Because of the higher energy of the gamma emissions and the short
half-life of 81mKr, images obtained with this gas can be alternated with
those obtained with 99mTc MAA.
• D. When 99mTc labeled aerosol imaging is performed before 99mTc MAA
perfusion imaging, smaller amounts (20-40 MBq) [0.5-1.0 mCi]) of 99mTc
labeled aerosol should be administered to the lungs.
Normal Ventilation/Perfusion