Lung Vent Imaging (Inert Gas) Flashcards
What are the applications of lung ventilation imaging?
-Assesses for pulmonary ventilation, lung function as it relates to the inhalation and exhalation of a radioactive gas or aerosol
-Increases sensitivity to pulmonary embolism
-Evaluates COPD
+Requires patient cooperation and must be done before perfusion study
What are the 2 methods of lung ventillation?
-Inert gases
-Radioaerosols
What are the indications for V/Q imaging?
-Pulmonary embolism: Degree of resolution of PE, acute vs. chronic
-Differential pulmonary function before surgery for lung Ca
-Evaluation of congenital heart or pulmonary disease: Cardiac shunts, pulmonary artery stenosis
-Evaluation of chronic pulmonary disorders: Cystic fibrosis
-Evaluation of the cause of pulmonary hypertension
What are conditions caused by asthma?
-Emphysema
-Pneumonia
-Bronchitis
Describe a hypoxia response and what it would appear as on ventilation images.
-Normal response is vasoconstriction
-Blood is shunted to areas of aerated lung tissue
-Matched defect as a result:
-Decreased perfusion
-Decreased ventilation
-PE cases: Ventilation should be normal or unchanged
What are the characteristics of an ideal lung vent agent?
-Can be used after perfusion images
-Optimal for imaging
-Closely models respiration
-Sufficient effective half-life
What are the most ideal ventilation RPs?
- 133-Xenon
- 127-Xenon
- 81m- Krypton
- Technegas/Pertechnegas
What are the characteristics of 133-Xenon? (Dose, energy, t1/2,etc.)
-Dose: Adult- 740 MBq, Peds- 0-12 MBq/kg; 3 mCi/min
-Not portable
-Energy: 81KeV
-T1/2: 5.3 days
-Inexpensive
-Preferred
-USA
-Biological T1/2: 30-45 sec during washout
What are the characteristics of 127-Xenon? (Dose, energy, t1/2,etc.)
-Dose: 370-740 MBq
-Not portable
-T1/2: 36.4 days
-Energy(s): 172, 203, 375 (203)
-Expensive
What are the characteristics of 81m- Krypton? (Dose, energy, t1/2,etc.)
-Dose: 296-370 MBq
-T1/2: 13 seconds, requires continuous elution from generator
-Energy: 176-192 KeV
-Single breath, wash in only
-Portable
-Expensive
-Not available in US
What is the patient positioning for vent?
-Posterior positioning
-Lower lobes visualized
-Largest lung volume
-Most common site of PE
-Decreases attenuation
-Sitting vs. supine
Describe wash in images
-Single breath
-Regional ventilation
-20 sec breath hold
Describe equilibrium images
-Distribution of aerated lung volume
-3 sequential 90 sec during normal breathing
-3-4 mins
- +/- obliques
Describe the Xenon-133 Vent procedure
-Breath in and out
-Wash in: Introduce RP, breathe in and hold breath as long as possible
-Equilibrium: Instruct patient to rebreathe RP and O2 for 2-3 mins, 2 dynamic images taken
-Wash-out: Patient breathes room air mixed with O2 while exhaling into Xe trap, 5 min dynamic or until washout is complete
What are the camera room requirements for Xe-133?
-Negative pressure: Unable to perform xenon at bedside
-Dedicated Xenon trap/exhaust vent or activated charcoal trap placed on the floor
What are disadvantages of using Xe-133?
-Limited number of views
-81 KeV is not ideal for gamma camera imaging (140 KeV Tc-99m)
-Negative pressure room requirement
-Must be performed before perfusion
What are normal vent results?
Inhaled gas readily diffuses into all areas of the lungs
-radioactive gas readily washes out
What are abnormal vent results?
-Wash-in: is delayed or absent in obstructed area
-Equilibrium: has partial diffusion in affected areas
-Wash-out: Slow clearance of abnormal areas, normal areas clear quickly
-Give appearance of hot areas when gas is trapped and has slow washout
