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Biomedical subjects

M Krix

Publications and source records attributed to M Krix.

7 recordsLinked to original sources
PubMed2006

[Ultrasound contrast media--principles and clinical applications].

This article reviews the technical basics and the application of contrast-enhanced ultrasonography. Ultrasound contrast agents have been evaluated in various organs and have proven to be particularly useful in the detection and characterization of liver lesions. Experiences in small parts (such as breast, or lymph nodes) are so far limited, because only since recently are the technical prerequisites available for contrast-enhanced ultrasound high-frequency transducers. Ultrasound contrast media can be used for functional studies, e. g., of organ or tumor perfusion. Mathematical models were primarily developed for measuring myocardial perfusion and have recently been adapted for studying tumors. In animal experiments as well as in clinical applications, quantitative parameters of tumor perfusion have been evaluated as surrogate parameters for response to radiotherapy, chemotherapy, or treatment with anti-angiogenic agents.

Algorithms↗
PubMed2005

Monitoring of liver metastases after stereotactic radiotherapy using low-MI contrast-enhanced ultrasound--initial results.

The purpose of this study was to monitor liver metastases after radiotherapy using contrast-enhanced ultrasound (CEUS). In 15 patients, follow-up examinations after stereotactic, single-dose radiotherapy were performed using CEUS (low mechanical index (MI), 2.4-ml SonoVue) and computed tomography (CT). Besides tumor size, the enhancement of the liver and the metastases was assessed at the arterial, portal venous, and delayed phases. The sizes of the tumor and of a perifocal liver reaction after radiotherapy measured with CEUS significantly correlated with those measured at CT (r=0.93, p<0.001). CEUS found a significant reduction of the arterial vascularization in treated tumors (p<0.05). In the arterial phase, the perifocal liver tissue was hypervascularized compared to the treated tumor (p<0.001); in the late phase, it was less enhanced than the liver (p<0.001) and more than the tumor (p<0.01). The perifocal liver reaction was also seen in CT, but with a variable enhancement at the arterial (50% hyperdense compared to normal liver tissue), venous, or delayed phase (each with 70% hyperdense reactions). CEUS allows for the assessment of tumor and liver perfusion, in addition to morphological tumor examination, which was comparable with CT. Thus, changes of tumor perfusion, which may indicate tumor response, as well as the perifocal liver reaction after radiotherapy, which must be differentiated from perifocal tumor growth, can be sensitively visualized using CEUS.

Contrast Media↗
PubMed2005

[Vascular imaging with contrast-enhanced sonography for experimental use].

The possibility of employing contrast-enhanced ultrasound for sensitive detection of perfusion has resulted in new forms of application in fundamental medical biological research that go far beyond mere preclinical evaluation of these techniques. This contribution explains the methods for visualization and quantification of perfusion with contrast-enhanced sonography and provides an overview of how these functional examinations have been used to date. The procedure is generally considered indicated when information on tissue perfusion using ultrasound is required. This topic is also gaining increasing clinical interest, e.g., for assessment of myocardial, cerebral, and renal perfusion or for monitoring therapy. Among the various new treatment procedures that have been investigated in animal models with ultrasound, particularly pro-angiogenic and antiangiogenic therapy approaches predict promising new fields for application of contrast-enhanced ultrasound.

Animals↗
PubMed2003

[Quantification of tissue perfusion with novel ultrasound methods].

Perfusion describes an important parameter of tissue vitality, e. g. of the myocardium, brain, or the kidney. In malign tumours, perfusion is of particular interest for characterization and prognosis. In addition, new pro- or anti-angiogenic therapies require a functional imaging which is suitable to quantify vascularity. Sonographic methods for the detection of microvascularity, particularly related smaller than those amenable to Doppler ultrasound, are reviewed. The main focus deals with the explanation of contrast-enhanced sonography using replenishment kinetics of microbubbles which provides a comprehensive quantification of tissue perfusion. Alterations of the microvascularity e. g., under anti-angiogenic therapy, can be depicted in experimental studies using this novel approach. Further clinical applications can be the quantification of the perfusion in the myocardium, the brain, or the kidney. New approaches to optimize the theoretical model to describe the replenishment, and novel technical developments are discussed.

Animals↗
PubMed2002

Magnetic resonance imaging of nude mice with heterotransplanted high-grade squamous cell carcinomas: use of a low-loaded, covalently bound Gd-Hsa conjugate as contrast agent with high tumor affinity.

RATIONALE: Malignant tumors often show an increased uptake and metabolism of plasma proteins, especially albumin. OBJECTIVES: Determine whether the accumulation of low loaded Gd-albumin improves visualization of malignant tumors by MRI. METHODS: Twelve nude mice with heterotransplanted squamous cell carcinomas were studied. The signal intensity of tumor, blood, liver, kidney and muscle tissue was studied in MR images after application of Gd-albumin during a period of 144 hours. MRI results were histologically correlated after simultaneously injection of Gd- and fluorescein-labeled albumins in 9 nude mice. RESULTS: Although liver and kidney had a maximum increase in signal intensity within 30 minutes, tumors showed a delayed 51% increase in the 24 hours after application. Histologic and fluorescence evaluation demonstrated albumin localization in tumors predominantly in stroma and necroses. CONCLUSIONS: Gd-albumin is efficiently accumulated in SCC transplants. MRI with low loaded Gd-albumin may offer relevant opportunities for recognizing tumors sensitive to a therapy with cyostic drug-labeled albumins.

Albumins↗
PubMed2000

Rigid piston approximation for computing the transfer function and angular response of a fiber-optic hydrophone.

The transfer function of a fiber-optic hydrophone (FOH) is computed for various fiber core radii. The hydrophone is modeled as a rigid disk, with plane waves impinging at normal or oblique incidence. The total sound field is written as the sum of the incident field and the field diffracted from the hydrophone. The diffracted field is approximated by the field generated by a vibrating planar piston in an infinite rigid baffle. For normal incidence and a pointlike fiber core, an analytical solution is presented. For finite fiber core radii, and for oblique incidence, the transfer functions are computed numerically. The calculated transfer functions exhibit an oscillatory frequency dependency that is most pronounced for small fiber cores. The solution for a core radius of 2.5 microm can be very well approximated by the analytical solution for a pointlike core at frequencies of up to 30 MHz. The results for normal incidence can be directly employed to deconvolute ultrasonic pressure signals measured with an FOH. From the transfer functions for oblique incidence, the angular response of the hydrophone is calculated. The angular response obtained here differs significantly from the model commonly used for piezoelectric hydrophones. The effective hydrophone radius derived from the angular response shows a strong frequency dependency. For low frequencies, it is found to be larger than the outer fiber radius, whereas it generally lies between the outer radius and the fiber core radius for frequencies above 10 MHz.

Acoustics↗