A. Ahmari, G. Baroud (Sherbrooke, Canada)
Vertebroplasty is a minimally invasive percutaneous procedure consisting of injecting cement into the vertebral body of a fragilized vertebra. The cement paste flow must be visualized in order to make sure no cement leakage out of vertebral body. Live visualization of paste flow is ensured by radiologic control (fluoroscopy), so that the physician can stop the injection at any time if leakage starts occurring. Although no minimum radiopacity is recommended for a bone cement to be used in vertebroplasty, but commercial cements in the market have around 35-45% conventional radiopacifiers (BaSO4and ZrO2) in their compositions or each group practicing vertebroplasty makes its own recipe . This study presents a design of an experiment to find the effect of radiopacifiers, concentration, and x-ray conditions on the visibility of acrylic bone cement.
METHODS: Based on the mixing procedure of acrylic bone cement that proposed by manufacture and formulation of cement which is designed (Table 1), liquid and powder are mixed and cylindrical samples are made.
Table (1): Factors and levels for this project
|A|Radiopacifier|4|BaSO4, W, Zr, Ta|
|B|Concentration (%)|2|10, 30|
|C|Voltage (KeV)|3|70, 90, 110|
|D|Current (mA)|3|100, 160,300|
The thickness and diameter of samples are 6 and 10 mm respectively. For each formulation, three samples are produced to increase the accuracy of experiment. Mixing conditions are the same for all batches. Samples are attached on the polymer plate and used for taking x-ray photos under different conditions and 10ms exposure time. To simulate in vivo conditions samples are inserted into 40cm water. Optical density of specimens read through x-ray photos by using optical densitometer.
The contrast index which is defined as the difference between optical density (OD) of the material under investigation and the background is shown in the Fig.1 and Fig.2. The results of statistical analysis show that (Fig.1) the increase of current of x-ray lamp from 100mA to 300mA affects the radiopacity of the material (ANOVA, p<0.0001) and improve contrast index of cements from 2.5 to 14% depend on the type and concentration of radiopacifier. With constant x-ray tube current of 100mA, most effective factor which shows big impact on contrast index (CI) is the concentration of radiopacifier (ANOVA, p<0.0001). Contrast index of bone cement improves 78 to 162% when the concentration of radiopacifier increases from 10 to 30% (Fig.2).In vertebroplasty, fluoroscopy in high voltage is more desirable due to lower x-ray absorption. High contrast index for the range of 90-110KeV belongs to tungsten (W) radiopacifier with 30% concentration compare to others. Fig.2- Contrast index of bone cement in constant x-ray tube current of 100mA. CONCLUSION: Although BaSO4 gives good radiopacity for cement but in high voltage (110KeV), tungsten is a good alternative radiopacifier. ACKNOWLEDGMENT: The authors thank R. Fradet and F. St-Onge for support provided for the x-ray photography. REFERENCES: 1. L. E. Jasper et al. , J. Mater. Sci. Mater. Med. 13 (2002)