[Optimal timing of contrast enhancement in coronary CT angiography using the Bolus-tracking method]

Reducing amount of contrast agent after compression of right brachial artery using a blood pressure cuff in computed tomography cerebrovascular angiography

OBJECTIVE

To invastgate feasibility of low-dose contrast agent in cerebral computed tomography angiography (CTA) to alleviate side effects.

METHOD

Siemens' Somatom Definition AS+CT scanner, Heine's blood pressure monitor G7-M237 (BP cuff) and Ultravist contrast agent (370 mg Iodine/ml) are used. CTA is acquired using following scan parameters including slice thickness of 1mm, image acquisition parameters of 128×0.6 mm, pitch size of 0.8 mm, 175 effective mAs, 120 kVp tube voltage, scan delay time of 3 seconds, and the scan time of 4 seconds. This study is conducted by securing the IV route in the left antecubital vein before injection of contrast agent, wrapping BP cuff around the branchial artery of the opposite right arm after setting the pressure to 200 mmHg. Then, the injection rate of the contrast agent is fixed at 4.5 cc/sec and contrast agent was injected in three different amounts (70, 80, and 100 cc). Bp cuff is released from this moment when HU value reachs 100.

RESULT

In this study, the mean HU values measured from common carotid artery are 412.45±5.89 when injecting 80cc contrast agent and using BP cuff and 399.64±5.51 when injecting 100 cc contrast agenet and not using BP cuff, respectively. In middle cerebral artery M1, the mean HU values are 325.23±38.29 when injecting 80cc contrast agent and using BP cuff and 325.00±30.63 when injecting 100cc contrast agent blood and not using pressure cuff, respectively. Difference of mean HU values is not statistically significant (p > 0.05) with and without using BP cuff.

CONCLUSION

This study demonstrates that reducing amount of contrast agent is possible when the right brachial artery is compressed using BP cuff. Study results indicate that reducing 20% injection of contrast agent in CT cerebrovascular angiography can still yield comparable imaging results with conventional contrast angent usage, which implies that less side effects are expected with a contrast agent injection. Thus, this study can serve as a reference for potential reducing side effect during CT cerebrovascular angiography.

[Development of test bolus tracking method and usefulness in coronary CT angiography]

The test bolus tracking (TBT) method is a new injection method of contrast medium that we developed. The TBT method is an injection technique that continuously performs the test bolus injection and the main bolus injection, such that the best acquisition of scan timing and the improvement of examination efficiency can be expected. We compared the TBT method and the test injection method by coronary CT angiography. The results demonstrated that the contrast enhancement of the coronary arteries was high and the variation of the CT value was also small in the TBT method. When the scan timing expected by the TI method and the TBT method were compared, it was different of two seconds or more by the case with 43%. However, the variation of CT value was small for the TBT method in these cases. Therefore, the TBT method is a very useful method for CCTA.

[Optimization of contrast injection protocol for coronary CTA: adjustment of injection iodine volume on test bolus parameters and patients' sex and BSA]

The purpose of this study was to correlate test bolus (TB) parameters and patient information and cardiac function with main bolus (MB) contrast density for 64-slice computed tomography, and to evaluate MB contrast density on a fixed injection rate, in comparison with an injection rate adjusted with TB parameters and patient information. A total of 256 patients underwent coronary CT angiography. In 126 patients (group 1), contrast material was administered at a flow rate of 4 ml/sec. The peak enhancement, the time needed to reach the peak of the TB and cardiac function of the MB were calculated for each patient in this group. The dependency of MB contrast attenuation on these parameters was evaluated. Significant correlations were obtained between the peak density of the TB and the patient's body surface area (BSA) with the enhancement of MB. Furthermore, females showed a higher peak enhancement of MB than males. In view of the results of group 1, in the other 130 patients (group 2) injection protocols were computed by using regression analysis of each patient's attenuation response to a TB and patient sex and BSA. Compared with group 1, the variations of MB contrast density of group 2 were reduced. Optimized contrast injection protocols are useful to reduce variations of MB contrast density, by taking these TB parameters and patient sex and BSA into account.

Impact of right ventricular contrast attenuation on the accuracy of right ventricular function analysis at cardiac multi-detector-row CT

PURPOSE

To investigate the impact of right ventricle (RV) contrast attenuation on the accuracy of RV function analysis at cardiac CT performed for coronary imaging.

MATERIALS AND METHODS

We analyzed multi-phase cardiac dual-source CT studies of 40 consecutive patients (mean age 60.9+/-12.3 years; 13 women) with normal valve function. Function analyses of both the right and left ventricle (RV and LV) were performed using dedicated post processing software and stroke volumes (SV) were computed for each ventricle. The accuracy of the RV-SV measurements was determined based upon comparison to LV-SV measurement. The level of contrast attenuation of the RV was recorded at three separate regions of interest-below the pulmonary valve, mid-ventricular, and inferior RV. The accuracy of RV function assessment was correlated with the level of attenuation using regression analyses.

RESULTS

There was a statistically significant correlation between the accuracy of RV function assessment and the level of RV attenuation in the inferior RV (adjusted R(2)=73.1%, p<0.0001). When compared to LV-SV measurements, in studies with low RV attenuation (<175 HUs, n=19) the mean deviation of RV-SV from LV-SV was 29.0+/-10.8 ml (42.1+/-13.9%). In studies with high RV attenuation (> or =175 HUs, n=21) the mean deviation of RV-SV from LV-SV was significantly lower 6.9+/-10.5 ml (9.9+/-16.0%).

CONCLUSION

The accuracy of RV function analysis is dependent on the level of contrast medium attenuation achieved in the inferior RV. There should be at least intermediate attenuation (>175 HUs) to enable accurate functional analysis. At low attenuation levels RV function parameters are prone to underestimation.