In order to study acute changes in perfusion with intracoronary thrombolytic therapy, we have used ten times the pretherapy intracoronary thallium-201 dose for the posttherapy study. Because of the larger posttherapy dose, the postthcrapy images had ten times as many counts as the pretherapy images. Since the change in image quality between the prethcrapy and posttherapy studies might affect interpretation, we studied the effect of image statistics on interpretation of perfusion scintigraphy. The pretherapy and posttherapy images were scored on a four-point scale in five segments on each of three views. In 31 patients, Poisson- distributed pseudorandom noise was added to the posttherapy study in order to match the statistical accuracy of the pretherapy study. A blinded interpretation of the pretherapy and posttherapy noise-added images was performed in the same way as the initial unblinded interpretation. The mean difference between the unblinded pretherapy and posttherapy scores (the improvement in thallium distribution with therapy) was 2.5+/-0.8 (standard error) compared with the difference between the blinded pretherapy and posttherapy noise-added scores which was 2.6+/-1.0. The correla-tion between readings of similar pairs of data was higher than the correlation between pretherapy and posttherapy studies. Thus, the difference in statistic quality of the pretherapy and posttherapy studies did not affect the interpretation of these studies. Therefore, our evaluation of pretherapy and posttherapy studies using a ten-fold increase in thallium-201 dosage is valid.
- Myocardial infarction