Single-Molecule Conductance of Redox Molecules in Electrochemical Scanning Tunneling Microscopy

Experimental data and theoretical notions are presented for 6-[1'-(6-mercapto-hexyl)-[4,4']bipyridinium]-hexane-1-thiol iodide (6V6) "wired" between a gold electrode surface and tip in an in situ scanning tunneling microscopy configuration. The viologen group can be used to "gate" charge transport across the molecular bridge through control of the electrochemical potential and consequently the redox state of the viologen moiety. This gating is theoretically considered within the framework of superexchange and coherent two-step notions for charge transport. It is shown here that the absence of a maximum in the Itunneling versus electrode potential relationship can be fitted by a "soft" gating concept. This arises from large configurational fluctuations of the molecular bridge linked to the gold contacts by flexible chains. This view is incorporated in a formalism that is well-suited for data analysis and reproduces in all important respects the 6V6 data for physically sound values of the appropriate parameters. This study demonstrates that fluctuations of isolated configurationally "soft" molecules can dominate charge transport patterns and that theoretical frameworks for compact monolayers may not be directly applied under such circumstances.

Quantitative assessment of iron-oxide-enhanced magnetic resonance imaging of the liver: Vessel isointensity is a potential characteristic of liver hemangiomas on late T1-weighted images

PURPOSE

To test whether a new quantitative measure, the tumor-to-vessel ratio, obtained from late post-iron-oxide-enhanced T1-weighted images allows for differentiating hemangiomas from liver metastases or all malignant liver lesions.

MATERIAL AND METHODS

Twenty-six patients (mean 57, range 33-79 years) were prospectively studied at 1.5T magnetic resonance imaging (MRI) with a T1-weighted 2D fast low-angle shot (FLASH) sequence (repetition time/echo time/flip angle; 200 ms/4.8 ms/90 degrees ) and a T2-weighted turbo spin-echo sequence (4072 ms/99 ms/180 degrees ). Imaging was carried out before and at intervals up to 18 min after IV injection of Ferucarbotran (Resovist, Schering, Germany). In 19 patients, one representative malignant lesion was analysed. Eleven hemangiomas were evaluated in 7 patients. Two readers performed a consensus reading with a signal intensity measurement in a lesion, normal liver and hepatic veins, from which ratios were computed.

RESULTS

On T1-weighted iron-oxide-enhanced MRI of 30 lesions, tumor-to-vessel signal intensity ratios were distinct in hemangiomas (median 1.04, range 0.99-1.10) as opposed to either metastases (0.64, 0.33-0.77; P < 0.05) or all malignant lesions taken together (0.64, 0.33-0.98; P < 0.05), while the tumor-to-liver ratio was not.

CONCLUSION

The tumor-to-vessel ratio may help to differentiate between hemangiomas and metastases. A ratio greater than 0.98 allowed differentiating hemangiomas from metastases with a wide safety margin.

[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.

Detection of hepatic metastases with low MI real time contrast enhanced sonography and SonoVue

AIM

SonoVue is the first ultrasound contrast agent which allows repeated continuous examination of the liver in real time. The aim of this study was to compare low mechanical index (MI) real time contrast enhanced ultrasound of the liver, using the contrast agent SonoVue, with conventional B-mode sonography for the detection of hepatic metastases.

METHOD

40 patients with known malignancy and at least one liver lesion on conventional B-mode sonography were included. Conventional B-mode sonography was performed followed by contrast enhanced ultrasound (CEUS) of the liver in the arterial (< 30 sec), portal-venous (40-120 sec) and delayed phase (> 120 sec) after injection of SonoVue. CEUS was performed using contrast specific imaging and low MI (< 0.3). Number, location and size of metastases on baseline and CEUS were compared with CT or MRI (blinded reader).

RESULTS

37 patients had 128 metastases on CT or MRI. Baseline US showed 74 metastases confirmed by reference examination (69%), while CEUS yielded 109 metastases (sensitivity 90%) (p < 0.001). On CEUS, 35 additional metastases not seen on baseline but confirmed by reference imaging were detected in 14 patients (36%). In 8 patients, CEUS showed 13 metastases not seen on reference imaging.

CONCLUSION

Detection of hepatic metastases is substantially improved by low MI real time contrast enhanced ultrasound with SonoVue compared to conventional B-mode sonography.