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Biomedical subjects

Michel Claudon

Publications and source records attributed to Michel Claudon.

7 recordsLinked to original sources
PubMed2006

The kidney: imaging with microbubble contrast agents.

Conventional ultrasonography of the kidney is faced by limitations due to the poor contrast of B-mode imaging for parenchymal disease and limited sensitivity of color Doppler for the detection of intracortical capillaries and deep pedicular vessels. Ultrasound contrast agents (USCAs) overcome these limitations, allowing the development of new applications for renal blood flow imaging and quantification. These improvements result from the increased acoustic response obtained from the microbubbles, as well as from the development of pulse sequences for bubble-specific imaging. In radiology, the liver has been considered as the primary target for contrast because USCAs allow both detection and characterization of focal lesions. The kidney has been less studied because USCA kinetics do not provide the same obvious potential for tumor characterization, and most clinical trials for contrast-enhanced renal imaging were conducted using color Doppler. Despite this, the kidney offers promising applications as USCAs improve the detection of abnormal microvascular and macrovascular disorders. Contrast-enhanced US may become the modality of choice for diagnosis of renal artery stenosis and detection of a perfusion deficit, as well as for characterization of indeterminate renal lesions, atypical cystic lesions, and the identification of acute pyelonephritis.

Contrast Media↗
PubMed2005

Renal functional contrast-enhanced magnetic resonance imaging: evaluation of a new rapid-clearance blood pool agent (p792) in sprague-dawley rats.

OBJECTIVES: The objective of the present study was to compare P792, a new rapid clearance blood pool agent characterized by negligible interstitial diffusion but unrestricted glomerular filtration, with Gd-DOTA in both qualitative and quantitative aspects of renal functional magnetic resonance imaging. MATERIALS AND METHODS: Dynamic imaging was performed with a fast T1-weighted gradient-echo sequence on a 1.5-T magnet in 25 Sprague-Dawley rats, after injection of 13 micromol Gd/kg-1 of P792 (n = 10), 100 (n = 10), or 50 micromol Gd/kg-1 of Gd-DOTA (n = 5). Signal-time curves from 6 regions of interest (ROIs), including renal parenchyma and contents, were analyzed. RESULTS: Qualitative analysis depicted a typical pattern of temporal enhancement as previously described with extracellular gadolinium chelates, including early and brief enhancement of the aorta, renal vessels and cortex, quickly followed by enhancement of the medulla and then renal pelvis. However, a decrease in signal intensity was noted in the inner medulla and the renal pelvis approximately 90 seconds after bolus injection, being more marked when using the full dose of Gd-DOTA. Curve analysis showed a similar vascular phase within each parenchymal ROI, confirmed by similar upslopes, which ranged from 0.015 +/- 0.007 to 0.019 +/- 0.005. Following this initial phase, T1-enhancement appeared greater and longer within the medulla and renal pelvis, and subsequently in the whole kidney ROI with P792 (time to maximal enhancement (sec)/ enhancement rate: 85.5 +/- 15.9/3.1 +/- 0.4) as compared with Gd-DOTA full (53.0 +/- 18.9/ 2.7 +/- 0.3) or half dosage (65.2 +/- 20.1/ 2.2 +/- 0.2). The subsequent decrease in signal intensity, characterized by a downslope during the minute following maximal enhancement, was faster with Gd-DOTA (0.006 +/- 0.002) as compared either to P792 or half dosage Gd-DOTA (0.003 +/- 0.001). CONCLUSIONS: Due to its physicochemical and pharmacokinetic properties, P792 allows the use of a reduced dosage of gadolinium, resulting in less T2* effect without compromising T1 enhancement. Thus, P792 appears suitable for renal functional MR imaging.

Animals↗
PubMed2003

Improved detection of hepatic metastases with pulse-inversion US during the liver-specific phase of SHU 508A: multicenter study.

PURPOSE: To compare conventional B-mode ultrasonography (US) alone with the combination of conventional B-mode US and contrast material-enhanced (SHU 508A) late-phase pulse-inversion US for the detection of hepatic metastases by using dual-phase spiral computed tomography (CT) as the standard of reference. MATERIALS AND METHODS: One hundred twenty-three patients underwent conventional US, US in the liver-specific phase of SHU 508A, and single-section spiral CT. US and CT images were assessed by blinded readers. Differences in sensitivity, specificity, and the number and smallest size of metastases at conventional and contrast-enhanced US were compared by using CT as the standard of reference. Lesion conspicuity was assessed objectively (quantitatively) and subjectively by one reader before and after contrast material administration. RESULTS: In 45 of 80 (56%) patients with metastases, more metastases were seen at contrast-enhanced US than at conventional US. In three of these patients, conventional US images appeared normal. The addition of contrast-enhanced US improved sensitivity for the detection of individual metastases from 71% to 87% (P <.001). On a patient basis, sensitivity improved from 94% to 98% (P =.44), and specificity improved from 60% to 88% (P <.01). Contrast enhancement improved the subjective conspicuity of metastases in 66 of 75 (88%) patients and the objective contrast by a mean of 10.8 dB (P <.001). Contrast-enhanced US showed more metastases than did CT in seven patients, and CT showed more than did contrast-enhanced US in one of 22 patients in whom an independent reference (magnetic resonance imaging, intraoperative US, or pathologic findings) was available. CONCLUSION: Contrast-enhanced US improved sensitivity and specificity in the detection of hepatic metastases.

Adolescent↗
PubMed2003

Isolation of the arterial supply to the carotid and central chemoreceptors in the sheep.

The aim of our study was to develop and validate a simple surgical model in the sheep which allows control of the gas composition of the blood supplying the carotid and central chemosensitive area independently of the rest of the body. This approach was made possible due to the specific features of the cranial circulation in the sheep. An extracorporeal circuit, consisting of a pump and a gas exchanger, was placed at the level of the two common carotid arteries to create a pressure gradient between the carotid and the systemic systems and to reverse blood flow in the vertebral vessels via the occipital arteries. When a pressure gradient of about 40 Torr was created between the systemic and carotid circulation, we found that no blood could reach the carotid bodies and the medulla without passing though the extracorporeal circulation. This was established (1) by measuring vertebral blood flow; and (2) by injecting either a coloured suspension or particles labelled with (99m*)Tc into the systemic or the carotid circulation. The slope of the relationship between minute ventilation (V(E)) and systemic arterial P(CO2) (P(a,CO2)) during high CO(2) inhalation in seven hyperoxic vagotomised and anaesthetised sheep was dramatically reduced, but remained above zero, when P(a,CO2) was maintained constant in the cephalic circuit (0.11 +/- 0.15 vs. 0.70 +/- 0.35 l min(-1) Torr(-1) for the control tests). This residual V(E) response to CO(2) inhalation remains to be explained since it could not be accounted for by any of the chemical or circulatory changes occurring in the cephalic circulation. Nevertheless, this preparation provides an easy method of maintaining chemical and circulatory homeostasis at the chemoreceptor level.

Animals↗
PubMed2002

Contrast-enhanced sonography of the renal transplant using triggered pulse-inversion imaging: preliminary results.

The purpose of our study was to quantify renal transplant parenchymal sonographic enhancement using pulse-inversion imaging (PII) and intermittent emission after contrast administration by means of bolus and infusion techniques, and to evaluate renal perfusion functional indices. A total of 34 patients, presenting with minor abnormalities (n = 14) and cortical perfusion changes due to parenchymal disorders (n = 12) or renal artery stenosis (n = 8) were included. Cardiac-triggered contrast-enhanced PII ultrasound (US) was performed after administration of SHU 508 A (Schering AG, Berlin, Germany), using a high mechanical index, a frame rate of one image every four cardiac cycles for bolus study, and a decreasing frame rate for infusion study. Compared to baseline values, peak enhancement ratio ranged from 5.6 to 14.7 using a bolus administration, and reached a value of 2.1 to 4.0 using infusion technique. Qualitative analysis showed heterogeneous enhancement in most allografts presenting with acute parenchymal disease (p = 0.03). In bolus studies, time to peak, wash-in and wash-out slopes increased in renal transplants with parenchymal disease and renal artery stenosis (p = 0.0001). Infusion administration exhibited no plateau in signal level, and no significant difference in enhancement ratio was found between groups of patients. Triggered PII after contrast agent administration provides morphologic and quantitative information about cortical vascularity in renal transplants.

Adult↗
PubMed2001

Advances in ultrasound.

Significant advances have been recently introduced into various fields of technology, taking advantage of the use of new piezoelectric materials and the large diffusion of broadband transducers. Various types of modulation may be applied to the pulse characteristics, using single pulse, multipulse or multiline techniques, and resulting in improved spatial resolution and better penetration. Non-linear imaging uses the harmonics component, which is generated by tissues or by contrast agents. Different modalities can be used to separate harmonics from fundamental bands from the received signal. New Doppler modes have been developed, whereas grey-scale flow imaging allows the simultaneous imaging of blood flow and tissues. Compounding techniques improve the contrast resolution of tissues and reduce artefacts. If 3D techniques are now currently available, real-time 4D imaging has been recently introduced. Elastographic imaging is still under evaluation, but promising clinical results have been shown. Recent release of the DICOM specification has made the full integration of ultrasound to the PACS systems easier. All these advances indicate that the contribution and potential of ultrasound in patient management is still growing.

Equipment Design↗