[Color-coded duplex sonography and ultrasound contrast media--detection of renal perfusion defects in experimental animals]

Imaging Methods for Ultrasound Contrast Agents

Microbubble contrast agents were introduced more than 25 years ago with the objective of enhancing blood echoes and enabling diagnostic ultrasound to image the microcirculation. Cardiology and oncology waited anxiously for the fulfillment of that objective with one clinical application each: myocardial perfusion, tumor perfusion and angiogenesis imaging. What was necessary though at first was the scientific understanding of microbubble behavior in vivo and the development of imaging technology to deliver the original objective. And indeed, for more than 25 years bubble science and imaging technology have evolved methodically to deliver contrast-enhanced ultrasound. Realization of the basic bubbles properties, non-linear response and ultrasound-induced destruction, has led to a plethora of methods; algorithms and techniques for contrast-enhanced ultrasound (CEUS) and imaging modes such as harmonic imaging, harmonic power Doppler, pulse inversion, amplitude modulation, maximum intensity projection and many others were invented, developed and validated. Today, CEUS is used everywhere in the world with clinical indications both in cardiology and in radiology, and it continues to mature and evolve and has become a basic clinical tool that transforms diagnostic ultrasound into a functional imaging modality. In this review article, we present and explain in detail bubble imaging methods and associated artifacts, perfusion quantification approaches, and implementation considerations and regulatory aspects.

[Screening and diagnosis for eliminating renovascular hypertension. Value of 24-hour blood pressure monitoring and color-coded duplex ultrasound diagnosis]

BACKGROUND

Direct renal angiography is still the method of choice for identification of renal artery stenosis. Newer non-invasive diagnostic methods include color coded duplex sonography and also ambulatory 24-h blood pressure monitoring, since in a large proportion of patients with secondary forms of hypertension the usual blood pressure fall during nighttime disappears.

PATIENTS AND METHODS

In a prospective in-hospital study we investigated 86 patients with suspected renovascular hypertension. Circadian blood pressure was measured oscillometrically and color coded duplex sonography was performed immediately before direct renal angiography.

RESULTS

Angiography revealed renal artery stenosis (> or = 50%) in 42 patients. This compared to a sensitivity of 92.9% and specificity of 91.7% for the use of sonography in those patients (70.4%) who could be adequately examined. Mean 24-h pressure values as well as standard deviations of blood pressure means as an indicator for blood pressure variability were not different in the 2 groups of patients, when all the data were analysed together and also when the data for nighttime and daytime were examined separately. The percent of blood pressure fall during nighttime was also not different in the 2 groups. In both groups 4 hypertensive patients had a blood pressure increase during nighttime. In 11 patients without renal artery stenosis a blood pressure fall of < 10% was observed, compared to 12 patients with renal artery stenosis. The circadian pattern of pulse rate was similar in both groups.

CONCLUSION

We conclude that ambulatory blood pressure monitoring has a considerably lower diagnostic value for renal artery stenosis compared to angiography and also to color duplex sonography. This method therefore does not appear to be an appropriate screening approach for this kind of secondary hypertension. The color coded duplex sonography, however, seems to be the best non-invasive diagnostic method in those patients, who can be adequately examined.

A transpulmonary contrast medium enhances the transcranial Doppler signal in humans

BACKGROUND AND PURPOSE

Transtemporal insonation in transcranial Doppler sonography is often impaired by an insufficient signal-to-noise ratio, especially in elderly patients. A transpulmonary stable air microbubble suspension was injected intravenously in humans as an intracranial ultrasonic contrast agent.

METHODS

In a clinical phase II study, 20 patients (15 women, 5 men; mean age, 65.5 +/- 11.5 years) presenting with clinical indications for transcranial Doppler investigation were examined. A total of 97 intravenous injections with different concentrations (200, 300, and 400 mg/mL of suspension) of air microbubbles bound to galactose microparticles as a carrier were performed. The signal enhancement of color-coded pulse curves of basal cerebral arteries was evaluated off-line in comparison to an integrated color-coded decibel scale, considering quality, quantity, and time course of enhancement requiring a 3-dB level above the native signal. The overall diagnostic information was assessed according to a reliability score.

RESULTS

The first acoustic signal increase was registered after an average of 21 seconds. Time intervals for a dose-dependent peak intensity and maximal duration were 41.3 +/- 17.1 seconds and 118.0 +/- 69.8 seconds (200 mg/mL); 55.5 +/- 27.7 seconds and 237.0 +/- 112.3 seconds (300 mg/mL); and 66.1 +/- 31.8 seconds and 293.0 +/- 122.0 seconds (400 mg/mL), respectively. Duration of signal enhancement increased significantly (P < .05) with higher concentrations. The extent of signal enhancement during the whole pulse curve reached an average of 9.1 +/- 5.0 dB for 200 mg/mL, 12.0 +/- 5.4 dB for 300 mg/mL (significant on P < .05 level), and 13.1 +/- 5.6 dB for 400 mg/mL concentration (P = NS). Respective maximal intensity spots reached 17.5 +/- 6.0, 20.7 +/- 5.5, and 22.7 +/- 5.9 dB for increasing concentrations, respectively. Overall visual assessment of enhanced pulse curves for diagnostic reliability showed a sufficient result in 38.1% of all injections with 200 mg/mL, in 88.6% with 300 mg/mL, and in 84.2% with 400 mg/mL concentration. Minimal side effects occurring in 12.4% of all injections were all reversible.

CONCLUSIONS

Transpulmonary stable air microbubbles bound to a galactose carrier represent a useful and safe contrast agent in case of an insufficient native signal in transcranial Doppler investigation.