Milliwatt-class broadband THz source driven by a 112 W, sub-100 fs thin-disk laser.

We demonstrate a high repetition-rate, single-cycle THz source with a maximum average power of 1.35 mW, operating at a center frequency of 2 THz. This result was obtained by optical rectification (OR) in GaP using an amplifier-free, nonlinearly compressed modelocked thin-disk oscillator based on Yb:YAG, delivering 8.4 µJ pulses with 88 fs duration at a repetition rate of 13.4 MHz, resulting in driving pulses for OR with 112 W average power and 80 MW peak power. To the best of our knowledge, our result represents the highest average power so far achieved with OR in GaP. The demonstrated performance is very attractive for improving current linear THz time-domain spectroscopy experiments, which are currently restricted by low signal-to-noise ratio and long measurement times.

Optical rectification of a 100 W average power mode-locked thin-disk oscillator.

We demonstrate terahertz (THz) generation at megahertz repetition rate by optical rectification in GaP crystals, using excitation average power levels exceeding 100 W. The laser source is a state-of-the-art diode-pumped Yb:YAG SESAM-mode-locked thin-disk laser, capable of generating 580 fs pulses at an average power up to 120 W and a repetition rate of 13.4 MHz directly from a one-box oscillator, without the need for any extra amplification stages. In this first demonstration, we measure a maximum THz average power of 78 µW at a central frequency of 0.8 THz. Our results show that optical rectification of state-of-the-art high average power ultrafast sources in nonlinear crystals is within reach and paves the way toward high average power, ultrafast laser pumped THz sources.

[Automated mammary sonography and mammography: the differentiation of benign and malignant breast lesions]. / Automatisierte Mammasonographie und Mammographie: Differenzierung benigner und maligner Mammaläsionen.

PURPOSE: A prospective study on the differentiation of breast lesions was carried out using experimental combination schemes of mammography and automatic sonography. MATERIALS AND METHODS: X-ray mammograms and a B image from automatic sonography of 39 malignant and 41 benign lesions as well as 40 cases without lesions were separately examined by four experienced diagnosticians. The observers differentiated the findings mammographically and by measurement in the B images. RESULTS: For two examiners the combination of mammography and automatic sonography gave with regard to the differentiation of breast lesions an improvement in sensitivity of 3 or 5% and in specificity of 31 and 18%, respectively, as compared to mammography alone while for the other two examiners an improved specificity of 21 and 36%, respectively, was accompanied by an 8 and 10% decrease in sensitivity as compared to mammography alone. CONCLUSIONS: The differentiating criteria from automatic sonography and mammography can, in principle, be used to evaluate the dignity of breast lesions. However, an optimization is necessary since the improvement in specificity does not compensate the loss in sensitivity.

Detection of malignant and benign breast lesions with an automated US system: results in 120 cases.

PURPOSE: To evaluate clinically an automated ultrasound (US) system for detecting benign and malignant breast lesions. MATERIALS AND METHODS: A prototype automated US system was used to examine 119 patients: 38 patients with 39 proved malignant breast lesions (7-50 mm), 41 patients with 41 proved benign breast lesions (8-40 mm), and 40 patients without breast lesions. The device yields a three-dimensional set of B-mode scans and reconstructed US images comparable to mammograms. All patients had undergone mammography. Four radiologists who had not performed the examinations independently assessed the mammograms and US images to detect benign and malignant breast lesions. RESULTS: Each of the four readers did not recognize one to three detectable malignant lesions on mammograms, one to two detectable malignant lesions on US images, two to four detectable benign lesions on mammograms, and five to seven detectable benign lesions on US images. All readers identified the 39 cancers with at least one of the modalities. The 40 cases without lesions were diagnosed correctly more frequently on the US images by three readers and on the mammograms by one reader. CONCLUSION: Depiction of breast lesions at automated US is reproducible. Automated US is complementary to mammography.

[Screening and diagnosis for eliminating renovascular hypertension. Value of 24-hour blood pressure monitoring and color-coded duplex ultrasound diagnosis]. / Screening and Diagnostik zum Ausschluss einer renovaskulären Hypertonie. Stellenwert der 24-Stunden-Blutdruckmessung und der farbkodierten Duplexsonographie.

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.

Minimally invasive catheter implantation for regional chemotherapy of the liver: a new percutaneous transsubclavian approach.

PURPOSE: Development of a percutaneously implantable catheter system for regional chemotherapy of liver metastases and its application in patients with surgically implanted but dislocated catheters. METHODS: Thirty-three patients with liver metastases of colorectal tumors were submitted to percutaneous puncture of the subclavian artery and insertion of a catheter whose tip was placed in the proper hepatic artery and whose end was subcutaneously connected with an infusion pump. RESULTS: The mean duration of therapy via the percutaneously inserted catheter was 27 weeks (+/-14 weeks). The most frequent complication was disconnection of the therapy catheter from the tube of the infusion pump. Eighty percent of all complications were corrected by reintervention. The therapy drop-out rate due to catheter-associated complications was 9%. CONCLUSION: Percutaneous insertion of a catheter for regional chemotherapy of the liver is a relatively uncomplicated method with high patient acceptance and simple access for reintervention.

Percutaneous vascular access guided by color duplex sonography.

Color duplex sonography (CDS) is primarily applied as a diagnostic procedure. It has not yet established itself as an aid in punctures or other interventions. The aim of this study was to evaluate the value of CDS in arterial and venous vascular punctures. One hundred and sixty-five CDS-assisted vascular punctures were performed in a prospective study after three unsuccessful palpation-guided vasopunctures or in the absence of a palpable pulse. All CDS-assisted punctures were successful. The duration of each attempted puncture showed no statistically significant difference compared with the palpation-guided puncture technique. In the cases with three unsuccessful palpation-guided vascular punctures, the CDS-assisted technique was successful after 1.66 attempts on the average. It is concluded that CDS-assisted vascular puncture is a fast and safe alternative for puncturing a pulseless vessel or for puncturing under difficult conditions.

Arterial angiography in high-kilovoltage technique with gadolinium as the contrast agent: first clinical experience.

Iodine-containing contrast agents are currently used for angiography. However, due to the relatively low atomic number of iodine, imaging must be performed with a relatively low tube voltage. Gadolinium has been used for several years as a contrast agent in MRI with low adverse side effects. This substance has a higher atomic number as compared with iodine. We investigated whether the use of a gadolinium-containing contrast agent with a higher tube voltage reduces the radiation exposure in angiography, and how the image quality compares with the previous technique. A total of 15 patients were examined with either a survey angiography or a selective angiography. In all patients angiography was performed with an iodine-containing contrast agent with a tube voltage of 75 kV. Then gadolinium-containing contrast agent was administered immediately with a tube voltage of 110 kV. Radiation exposure and image quality were compared. On average, a dose reduction factor of 3.57 times was achieved by using 110 instead of 75 kV. However, the image quality was poorer in the majority of cases as compared with the images taken with iodine as a contrast agent and a tube voltage of 75 kV. The poorer image quality is caused by the relative low concentration (0.5 M) of the used gadolinium solution. A 1 M solution is currently tested for market approval and would probably solve this problem.

Evaluation of acute scrotal pain by color-coded duplex sonography.

In light of the high sensitivity of color-coded duplex sonography (CCDS), we analyzed a group of patients with acute scrotal pain to evaluate the use of CCDS in routine clinical examination. During March 1988 through April 1991, CCDS was used in 31 patients with acute scrotal pain before they underweight surgery in our department. In 15 patients, the structural and perfusion changes of the scrotal contents were such that a definitive diagnosis was possible. In the rest of the patients, the pathologic changes seen with CCDS were more complex, and the correct interpretation needed more expertise; this was especially true in patients with partial torsion, posttorsion status, and torsion of hydatids. CCDS with the simultaneous display of anatomic scrotal structures and blood flow over the entire scan field is an excellent method for evaluating patients with acute scrotal pain. However, apart from the classical case of no perfusion (as in testicular torsion) and increased perfusion (as in inflammation), more complex changes are more difficult to interpret. The correct diagnosis in the latter cases requires considerable experience and evaluation of all facts, including clinical history, results of palpation, and structural and perfusion changes of the scrotal contents.

Color-coded duplex sonography for noninvasive diagnosis and grading of renal artery stenosis.

The accuracy of color-coded duplex sonography (CCDS) in screening hypertensive patients for renal artery stenosis (RAS) was assessed using a semi-quantitative waveform analysis. Our special aims were to separate between moderate and high grade stenoses and to evaluate the accuracy of the method in imaging both the whole course of the renal arteries and accessory renal arteries. Included in the prospective, angiographically controlled study were 135 consecutive patients with 268 renal arteries, of which 195 arteries (73%) could be visualized both proximally and distally by CCDS. Only three of 15 accessory renal arteries could be identified by CCDS. In 42 RAS > or = 50% sensitivity of CCDS was 93%, specificity 92%, and overall accuracy 92%. The sensitivity in identifying RAS > or = 75% was 92%, and none of the high grade stenoses were missed. Because of difficulties in visualizing the middle portion of the renal artery, we carefully examined this part of the artery in 116 additional patients. Whereas the proximal and the distal parts could be visualized in 77% of the renal arteries, signals from the middle third could be derived only in 60% on the right, and in 39% on the left side. Provided that the renal arteries were visualized both proximally and distally, a hemodynamically effective RAS could be excluded with high probability. Moreover, exact grading of high-grade stenoses was possible in all cases but one. An advantage of CCDS over conventional duplex sonography appears to be the time-saving examination. Since a low prevalence of RAS impairs the positive predictive value of CCDS, the examination should be reserved for patients with a strong clinical suspicion of renovascular hypertension.

Maturation of the testis: ultrasound evaluation.

We performed a prospective study to investigate whether the sonographic appearance of the testicular parenchyma changes during maturation of the testis. One hundred forty-three boys ranging in age from 6 months to 16 years, and 11 volunteers aged about 30 years, were included in the study. The echogenicity of each of the 308 normal testes were determined by measuring the average brightness of a histogram over a defined testicular area. To avoid divergent results due to different settings of the device in individual cases, the average brightness of a histogram of a standard ultrasound phantom was measured immediately after the examination of each testicle. From these 2 measurements, testicular echogenicity could be calculated independently of individual equipment settings. All testes had a homogeneous echotexture. The echogenicity of the prepubertal testis was markedly reduced compared to the medium-level echogenicity of the mature testis (p < 0.001). Testicular echogenicity increases during puberty. We conclude that testicular echogenicity increases with maturation. Knowledge of this fact may improve the diagnostic performance of scrotal ultrasound especially in children.

Magnetic resonance imaging-controlled laser-induced interstitial thermotherapy.

RATIONALE AND OBJECTIVES: Laser-induced interstitial thermotherapy (LITT) may become an attractive modality for minimally invasive tumor therapy. Magnetic resonance imaging (MRI) could be used to assist this procedure. METHODS: A T1-weighted turbo fast low-angle shot (FLASH) sequence for on-line monitoring of the laser-influenced region (liver, muscle) was investigated. Sequence parameters were optimized for maximal image contrast. Magnetic resonance imaging-controlled LITT was performed in vitro, in vivo (rabbits), and in 8 human investigations (6 patients). Special laser applicators were used to establish a uniform laser light distribution. RESULTS: With the MRI sequence used, the LITT region is visualized as a bright area outlined by a dark border. This dark border corresponds to an isotherm of 45 +/- 2 degrees C depending on the sequence parameters used. CONCLUSION: With the T1-weighted turbo-FLASH sequence, MRI can be used for on-line monitoring of interstitial laser-induced thermotherapy in moving organs.

[Sonography of malignant liver lesions: establishing the current status]. / Sonographie maligner Leberläsionen: Eine Standortbestimmung.

Ultrasound of the liver is the most widely used screening method to detect focal lesions in connection with malignant basic diseases. The efficiency of US is compared to that of other common imaging procedures, and new US methods, e.g. color-coded duplex sonography, intraoperative ultrasound, and the use of contrast agents, are discussed.

[Contrast media in ultrasound diagnosis]. / Kontrastmittel in der Ultraschalldiagnostik.

The combination of ultrasound contrast media (US-CM) and color-coded duplex sonography (CCDS) is a very promising new diagnostic method. The principles of CCDS and US-CM are therefore briefly discussed. Different US-CM are described regarding their application and possible indications. This is followed by a summary of the first clinical experience with this new method.

[Chemoembolization of liver tumors (VX-2) using lyophilized Spherex]. / Chemoembolisation von Lebertumoren (VX-2) unter Verwendung von lyophilisiertem Spherex.

Chemoembolisation is a new promising approach. Until now no standardized procedures exist for the production of the embolisate-cytostatics mixture. A main technical problem when doing chemoembolisation is the proof of the complete peripheral vascular occlusion. By using lyophilized Spherex and cytostatics, diluted in x-ray contrast media, frozen pictures can be obtained and the complete proof of the embolisation is possible. Therefore the conventional x-ray examination can be used to monitor the embolisation treatment instead of the much more sophisticated DSA technique.

[Color-coded duplex sonography and ultrasound contrast medium in the study of peripheral arteries--initial clinical experiences]. / Farbkodierte Duplexsonographie und Ultraschallkontrastmittel zur Untersuchung peripherer Arterien--Erste klinische Erfahrungen.

Ultrasound contrast agents (US-CA) amplify reflected sound waves. Most substances used as contrast agents are destroyed when passing the lungs. SH U 508 is a new US-CA that can pass the lungs without impairment after peripheral intravenous application. In a clinical trial of this US-CA, we investigated its effect on the visualization of blood movement in peripheral arteries by color-coded Duplex sonography (CCDS). The leg arteries of 20 patients with severe chronic arterial occlusion were examined by CCDS (QAD I and Platinum) after i.v. application of the US-CA. After passage of the pulmonary capillaries, the US-CA amplified blood flow signals in the arterial system in a dose-dependent manner with both systems used. Undesired side-effects were not observed. The amplification produced by appropriate concentrations of the US-CA markedly improved the visualization of blood movement. Further studies are required to determine the optimal dosage and application technique as well as the indication for using this US-CA.