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What are the 2 main group of lung pharmaceutical agents?
- 1. Perfusion (labeled particles)
- -Tc 99m Macroaggregated Albumin (MAA)
- 2. Ventilation Agents (gases and aerosols)
- -Xenon 133 (gas)
- - Tc 99m DTPA (aerosol)
How does the perfusion scan work?
1: MAA (20-60 microns) is trapped in smaller sized lung capillaries arterioles
- 2: PE causes regions of absent radioactivity
- NORMAL: no perfusion defects (hot)
- ABNORMAL: obstructed perfusion (cold), ventilation confirms this
List some biological properties of MAA
- 1. Particle clearance by fragmentation
- 2. T 1/2 depends on size of particle and hardness (how hot temp is when making particles)
- 3. Cleared particles are phagocytosed in RES with proteolytic digestion in Kupffer's cell.
What is the relationship between time, MAA particles and activity?
- Increases Decreases
- Time Activity
- #of MAA Particles
How big are MAA particles and how many are typically given to adult patients?
- size: 20-60 microns (too small, it goes to liver)
- # of particles:300,000 (3mCi)
* Dilute if suspected pulmonary hypertension*
What's the purpose of Lung Ventilation Imaging
- 1. Assess lung ventilation
- 2. Differentiate PE from COPD
What are the 3 phases of Vent study?
- Wash-In: (inhales Xe 133 10mCi)
- Equilibrium: pt re-breathes gas/O2 mixture (5min after inhalation)
- Wash-Out: Pt inhales air, Xe-133 exhaled
What does COPD and PE look like on vent and perf images?
- Vent Perf
- COPD Defect Defect
Pe Normal Defect
What 2 ways does MAA enter systemic circulation?
1. After fragmentation in lung (no risk)
*Max pt dose of 1mg MAA particles*
- 2. Via right-to left cardiac shunt (VSD- ventricular septal defect)
- -MAA bypassed lungs and ends up in kidney/brain.