1. Venous uptake of Tc-99m MIBI: An exploration of possible causes
Alexander Smout, Ann Fullbrook, Janine Ward, Louise Wright, John RW Hall
Department of Nuclear Medicine, Frimley Park Hospital, Frimley
Introduction
This work was done to investigate whether the incidence of venous visualisation could be decreased by introducing a 20ml saline flush and to establish what other factors affected the likelihood of incidence.
Uptake of Tc99m-MIBI in veins is a fairly common occurrence. While the amount of radioactivity in the veins, when observed, is typically only around 0.5% of that injected1, it has the potential to obscure the visualisation of adenomas on planar imaging.
Prospective Audit Design
The injection technique, administered activity, amount of saline flush and the specific vein that was injected were documented. Patient demographics and recent blood results were also included for analysis, where available.
The images were simply assessed as the injected vein being seen or not seen on the early and late planar images.
Anterior
15 minutes
Anterior
3 hours
Figure 1: Whole body anterior MIBI images showing the basilic vein at 15 minutes (left) and 3 hours (right).
Common Observations
The activity in the veins appears to clear slowly, as where veins were seen on the early images, they were also seen on the late images in all cases (Figure 1).
It was common to see uptake in the basilic / cephalic veins extending to the axilla and in a few patients the axillary and subclavian veins were also seen (Figure 2).
In patients that underwent multiple MIBI scans, the extent of uptake was similar in all of their scans in 10 of 11 patients, suggesting a clinical dependence (p(≥10)=0.01)
Figure 2: Uptake in the basilic, axillary and subclavian veins seen in an RAO 15 min image.
Figure 3: Uptake in collateral veins was seen in a few patients, which can obscure pathology
Results and Analysis
Injection Techniques
Results
Statistical Analysis
Statistical Significance
Right side vs left side
18/28 (right) vs 6/11 (left)
Odds Ratio 1.50
Not statistically significant (p = 0.58)
Saline flush – 20ml vs 5ml
9/16 (20ml) vs 15/23 (5ml)
Odds Ratio 0.69
Not statistically significant (p = 0.57)
Patient Demographics
Results
Statistical Analysis
Statistical Significance
Age
Ages 68±10 (seen) vs 71±13 (not seen)
T-Test
Not statistically significant (p = 0.30)
Sex
11/14 (male) vs 13/25 (female)
Odds Ratio 3.38
Not statistically significant (p = 0.11)
Multiple scans with similar uptake
10/11
Binomial, p{same}=0.53
Statistically significant (p{≥10} = 0.01)
Clinical Factors*
Results
Statistical Analysis
Statistical Significance
Erythrocyte sedimentation rate
13±15 (seen) vs 19±17 (not seen)
T-Test
Not statistically significant (p = 0.57)
Platelets
230±55 (seen) vs 390±190 (not seen)
Not statistically significant (p = 0.08)
Calcium
2.8±0.2 (seen) vs 2.7±0.2 (not seen)
Not statistically significant (p = 0.45)
Parathyroid Hormone
24±12 (seen) vs 10±7 (not seen)
Not statistically significant (p = 0.06)
* Results of other blood tests including full blood counts were also analysed however no statistically significant differences were seen.
Conclusion
The use of a larger saline flush, as suggested in literature1, did not reduce the incidence of venous visualisation in this study.
This work has shown that patients that have multiple MIBI scans are likely to have the same pattern of venous uptake in both of their scans (p = 0.01), which suggests that there is a clinical explanation for venous uptake rather than a technical reason.
As only 13 of our 39 patients had recent blood test results, the clinical basis of this uptake remains a mystery. Data collection is set to continue and further analysis looking at the absolute uptake in the veins may give us enough clues to identify the cause of this phenomenon.
Reference 1: Bearcroft P. 1994, 67(800):