Cardiovascular Journal of Africa: Vol 28 No 4 (July/August 2017)

CARDIOVASCULAR JOURNAL OF AFRICA • Volume 28, No 4, July/August 2017

AFRICA

231

was compared with 7 563 studies from 296 laboratories in 59

countries around the world.

Patient demographics, clinical characteristics and radiation

dose information for the African and non-African study cohorts

are presented in Table 2. African patients were younger compared

to patients from the rest of the world (60.2

11.0 vs 64.3

12.0

years;

0.0001). Median and mean patient ED were similar

in both populations. However, a larger proportion of African

patients received an ED ≤ 9 mSv (49.7 vs 38.2%,

0.001).

The distribution of individual African patient EDs is presented

in Fig. 1. African patients were more likely than non-Africans to

undergo an MPI study using a stress-only protocol [odds ratio

(OR): 3.4, 95% CI: 2.7–4.3,

0.001]. The use of PET imaging

was lower in African patients (1.7 vs 6.1%,

0.0001).

Patient volumes were similar for participating African and

non-African laboratories, as were the laboratory mean and

median ED and the proportion of laboratories with a median

ED ≤ 9 mSv (Table 2). However, there was significant variation

in the ED among African laboratories (median ED range: 2–16.3

mSv,

0.0001). African laboratory volumes and EDs are

presented in Table 3.

The overall adherence to best practices to minimise radiation

exposure was higher among African laboratories, as reflected

in the mean QI score (6.3

1.2 vs. 5.4

1.3,

0.013) and the

proportion of laboratories with a QI score ≥ 6 (75.0 vs 44.9%,

0.041). However, while the adherence to each individual

best practice was also higher among African laboratories,

this difference failed to reach statistical significance (Table 4).

The only exception was the use of stress-only imaging, which

was used in 66.7% of African laboratories and only 28.7% of

non-African laboratories (

0.005). The practices of weight-

based dosing and ensuring sufficient administered activity to

avoid shine through were both higher in African laboratories but

failed to reach statistical significance.

Discussion

Africa is facing difficulties in developing nuclear medicine in

general,

and the continent has the lowest ratio of clinical

nuclear medicine applications per capita. Few studies

15,16

explicitly

examine nuclear cardiology practice in Africa. The INCAPS

worldwide cross-sectional study of MPI provides a valuable

Table 1. Scoring and explanations of the eight best practices. Adapted from Einstein

et al

Best practice Scoring

Explanation

Avoid thallium

stress

One point if no thallium-201 studies were performed in

patients

≤

70 years old

SPECT imaging with thallium is associated with a considerably

higher radiation dose to patients compared with technetium-based

radiopharmaceuticals. This item excludes thallium viability studies

and stress redistribution–re-injection stress and viability studies

Avoid dual

isotope

One point if no dual isotope (rest thallium and stress techne-

tium) studies were performed in patients

≤

70 years old

Dual isotope imaging is associated with the highest radiation

dose of any protocol

Avoid

too much

technetium

One point if (1) no study was performed with technetium activ-

ities > 1 332 MBq (36 mCi), and (2) mean total effective dose

was

15 mSv for all studies with two technetium injections

1 332 MBq is the highest recommended activity in guidelines,

and 15 mSv is a very high radiation dose for a 99mTc study

Avoid too

much thallium

One point if for each study with thallium, less than 129.5 MBq

was administered at stress

The expert committee maintained that 129.5 MBq should be the

upper threshold for thallium activity

Perform stress-

only imaging

One point if the laboratory performed at least one stress-only

study, in which rest imaging was omitted, or if the laboratory

did only PET-based stress tests

If stress images are completely normal, subsequent rest imaging

can be omitted

Use camera-

based dose-

reduction

strategies

One point if the laboratory performed at least one study using

at least one of the following: (1) attenuation correction (CT or

transmission source), (2) imaging patients in multiple positions,

e.g. both supine and prone, (3) high-technology software (e.g.

resolution recovery and noise reduction), and (4) high-technol-

ogy hardware (e.g. PET or a solid-state CZT SPECT camera)

Each of these approaches reduces the administered activity

needed and facilitates performance of stress-only imaging

Weight-based

dosing for

technetium

One point if the laboratory had a statistically significant posi-

tive correlation between patient weight and administered activ-

ity (MBq), for injections of technetium

Tailoring the administered activity to the patient weight offers an

opportunity to reduce radiation dose

Avoid

inappropriate

dosing that

can lead to

‘shine-through’

artifact

One point if the laboratory performed no SPECT studies with

technetium rest and stress injections on the same day, in which

the activity of the second injection was less than three times

that of the first injection

Shine through occurs in one-day technetium studies when residu-

al radioactivity from the first injection interferes with the images

for the second injection. To avoid shine through, guidelines

recommend that the activity for the second injection should be

three to four times higher than the first injection. A second injec-

tion of less than three times of the activity of the first injection

constituted a dosing that can lead to shine through

Effective dose (mSv)

Number of patients

Fig. 1.

Distribution of radiation-effective dose among observed

African patients.