CARDIOVASCULAR JOURNAL OF AFRICA • Vol 21, No 3, May/June 2010
144
AFRICA
and fitted with low-energy, high-resolution collimators. Gated
SPECT imaging was performed using eight frames. Thirty
projection images, each of 25 seconds’ duration, were acquired
on a 64
×
64 matrix over a 90˚ counter-clockwise rotation with a
starting angle of 45˚ (step-and-shoot mode). A zoom of 1.45 was
applied resulting in a pixel size of 1.6 mm. A Butterworth filter
was applied (order 5, cut-off 0.4) and filtered back projection
was used for reconstruction. In addition, a static LAO and LPO
view was acquired for all patients for both the stress and rest
studies for 500-K counts (Fig. 3)
Statistical analysis
Sample size was determined based on similar studies published
recently. Pearson’s Chi-squared test was used to determine
whether the baseline characteristics of the two groups were
comparable. With the exception of dyslipidaemia, no statistically
significant differences were found. A two-sample
t
-test with
equal variances was used to determine the correlation between
observer evaluation and the MYO:EXT ratio. In addition, the
kappa statistic was calculated (using STATA 10) to evaluate
inter-observer agreement for more than two observers with two
possible outcomes (yes/no). A
p
-value of less than 0.05 was
considered statistically significant in all calculations.
Data analysis
Three experienced nuclear medicine physicians evaluated static
images (LAO and LPO views) of both the stress and rest studies
of all study participants for the presence or absence of interfering
extra-cardiac activity. Observers evaluated the images independ-
ently of one another and were blinded to the clinical information
as well as the protocol details.
The raw anterior data for both parts of each study were
selected and regions of interest (ROIs) were created as follows: a
circular semi-automatic ROI surrounding the myocardium of the
left ventricle and an irregular, manually drawn area starting from
the infero-lateral aspect of the myocardial ROI to the medial
aspect thereof (Fig. 4). ROIs were copied between stress and rest
studies of individual patients to increase reproducibility.
The mean counts per pixel were obtained for both ROIs and
were used to calculate the ratio between myocardial activity
(MYO) and extra-cardiac activity (EXT) for each patient in a
manner similar to the one described by Peace and Lloyd.
11
The
aim was to validate the use of the MYO:EXT ratio in quantifica-
tion of interfering extra-cardiac activity in our patient popula-
tion.
Results
The patient characteristics (Table 3) did not demonstrate any
statistically significant differences between the two study groups
in terms of demographics or co-morbidity (
p
>
0.05) with the
exception of dyslipidaemia, which was more prevalent in the
erythromycin group
All three physicians determined that the frequency of interfer-
ing extra-cardiac activity was higher in the erythromycin study
group when compared with the lemon juice group. Differences
between the two groups varied between 6 and 10% among the
various observers. Interference was consistently judged to be
Fig. 2. Randomisation process.
Erythromycin (90 studies)
Group A
Lemon juice (102 studies)
Group B
45
Stress
45
Rest
1
exercise
44
Persantin
51
Stress
51
Rest
1
exercise
1
Dobutrex
49
Persantin
Fig. 3. Static LAO and LPO view for all patients for both the stress and rest studies for 500-K counts.
Static myocardiac stress 2008/05/19
LAO 499K Duration: 80sec 256 x 256 Pix: 1.6mm 99mm Technetium LPO 502K Duration: 80sec 256 x 256 Pix: 1.6mm 99mm Technetium
%
66
0
%
66
0
TABLE 4. QUANTITATIVE RESULTS
Interfering extra-cardiac activity Erythromycin Lemon juice
Observer 1
42/90
(46.67%)
38/102
(37.25%)
Stress/rest
21/21
21/17
Observer 2
51/90
(56.67%)
50/102
(49.02%)
Stress/rest
28/23
28/22
Observer 3
55/90
(61.11%)
57/102
(55.88%)
Stress/rest
29/26
29/28
