ERNA Flashcards
ERNA acronym
Planar equilibrium radionuclide angiocardiography
ERNA use
Used to determine global and regional measures of ventricular function (primarily left LV function) at rest and/or during exercise stress or pharmacologic intervention.
Rest technetium 99m-labeled red blood cells
20-25 mCi/70kg body weight (11-13 MBq/kg)
Exercise technetium 99m-labeled red blood cells
25-35 mCi/70kg
Radiation dosimetry to pt from 20 mCi of Tc-99m-labeled RBCs labeled in vitro is:
0.3 to 0.52 rem effective dose equivalent
In vivo - slightly higher
Labeling methods
In vivo or modified in vivo/in vitro methods (e.g., using 2-3 mg stannous pyrophosphate 15 minutes before injection of the radiopharmaceutical)
Poor labeling of RBCs
free Tc-99m-pertechnetate accumulates in the mucosa of the stomach and in the thyroid gland
What interfere with RBC labeling
Heparin - complexes with Tc99m
Dextrose solution - Complexes with Tc-99m
Antibodies against RBCs (from methyldopa, quinidine, and PCN; present with CLL, non-Hodgkin’s lymphoma, and SLE/immune disorders)
Hydralazine - oxidation of stannous ion
Prazosin - decreases labeling rate
Propranolol - increase dissociation
Digoxin - decreases labeling rate
Doxorubicin - ?
Iodinated contrast - ?
Prolonged generator ingrowth - increased carrier
Decreased hematocrit - ?relative increase in plasma which oxidizes stannous ion
Excess stannous ion - Tc-99m reduced outside the RBC
Insufficient stannous ion - incomplete reduction with free Tc-99m pertechnetate
Collimator
For resting studies, use of a parallel-hole, high resolution collimator with spatial resolution of approximately 8-10 mm full width at half maximum, sensitivity (for Tc) of ~4000-5000 counts/s8mCi or 108-135 counts/s*MBq
If time-limited stress study (eg. bicycle exercise) - higher sensitivity (and therefore poorer spatial resolution) collimator may be considered, LEAP - 12 mm FWHM at 10 cm and sensitivity of ~10,000 counts/smCi or ~280 counts/sMBq)
Pixel size
Pixel size should not exceed 5mm.
Any matrix size that results in a pixel size less than approximately 4 mm/pixel (with approximately 2-3 mm/pixel being preferred) can be used.
FOV
Effective FOV is dependent on the camera size and acquisition zoom utilized.
18x18 cm^2 FOV will be sufficient.
Energy window
140 keV +/- 10% window
Bad beat/beat length winds (arrhythmia rejection)
accepting less than 10-15% arrhythmic beats are acceptable if only EF is assessed.
If diastolic function needed, beat length windowing (arrhythmia rejection) is necessary.
Frame rate
< 50 milliseconds/frame is preferred for resting EF
<30 milliseconds/frame if ejection and filling rates are to be computed
Resting study minimum 16-19 frames/cardiac cycle; 24-32 for EF calculations and ejection and filling parameters
Stress studies: R-R < 600 milliseconds, 32 frames/cycle preferred
Count density
Studies containing approximately 20,000 counts/cm2 (1,800 counts/pixel for a 3-mm pixel) over the center of the left ventricle at rest using high-resolution collimation, or about 40,000 counts/cm2 at rest with the higher-sensitiv- ity collimators (LEAP or high sensitivity), as used in rest/exercise studies, are preferred (which corresponds to about 3 to 4 million counts in a 15 9 15-cm2 FOV with high-resolution collima- tor).
