Christian Kollmann

Evaluation of a miniature electromagnetic position tracker

The advent of miniaturized electromagnetic digitizers opens a variety of potential clinical applications for computer aided interventions using flexible instruments; endoscopes or catheters can easily be tracked within the body. With respect to the new applications, the systematic distortions induced by various materials such as closed metallic loops, wire guides, catheters, and ultrasound scan heads were systematically evaluated in this paper for a new commercial tracking system. We employed the electromagnetic tracking system Aurora (Mednetix/CH, NDI/Can); data were acquired using the serial port of a PC running SuSE Linux 7.1 (SuSE, Gmbh, Nürnberg). Objects introduced into the digitizer volume included wire loops of different diameters, wire guides, optical tracking tools, an ultrasonic (US) scan head, an endoscope with radial ultrasound scan head and various other objects used in operating rooms and interventional suites. Beyond this, we determined the influence of a C-arm fluoroscopy unit. To quantify the reliability of the system, the miniaturized sensor was mounted on a nonmetallic measurement rack while the transmitter was fixed at three different distances within the digitizer range. The tracker was shown to be more sensitive to distortions caused by materials close to the emitter (average distortion error 13.6 mm +/- 16.6 mm for wire loops positioned at a distance between 100 mm and 200 mm from the emitter). Distortions caused by materials near the sensor (distances smaller than 100 mm) are small (typical error 2.2 mm +/- 1.9 mm). The C-arm fluoroscopy unit caused considerable distortions and limits the reliability of the tracker (distortion error 18.6 mm +/- 24.9 mm). Distortions resulting from the US scan head are high at distances smaller than about 100 mm from the emitter. The distortions also increase when the scan head is positioned horizontally and close to the sensor (average error 4.1 mm +/- 1.5 mm when the scan head is positioned within a distance of 100 mm from the sensor). The distortions are slightly higher when the ultrasound machine is switched on. We also evaluated the influence of common medical instruments on distance measurements. For these measurements the average deviation from the known distance of 200 mm amounted to 3.0 mm +/- 1.5 mm (undistorted distance measurement 1.5 mm +/- 0.3 mm). The deviations also depend on the relative orientation between emitter and sensor. The results demonstrate that the miniature tracking system opens up new perspectives with regard to surgery applications where a flexible instrument is to be tracked within the body. Significant distortions caused by metallic objects only occur in the worst cases, for example, in the presence of a closed, unisiolated wire loop or a C-arm fluorescence unit close to the emitter and which can be avoided by suitable usage.

IN VITRO THROMBOLYSIS ENHANCED BY STANDING AND TRAVELLING ULTRASOUND WAVE FIELDS

Success of thrombolytic therapy depends on penetration of recombinant tissue plasminogen activator (rt-PA) into clots. Ultrasound (US) of therapeutic quality accelerates thrombolysis in vitro. As yet, only the effects of travelling acoustic waves on thrombolysis have been investigated, and the impact of standing acoustic waves has been neglected. In the present study, we examined the effects of standing and travelling US wave fields applied continuously for 1 h (frequency 2 MHz, acoustic intensity 1.2 W/cm(2)) on thrombolysis enhancement by measuring clot weight reduction and concentration of fibrin degradation product D-dimer (FDP-DD) produced from clots subjected to rt-PA. The level of FDP-DD was 1.8 times greater in travelling than in standing acoustic waves. Thrombolysis enhancement was 46.0 +/- 20.8% in standing and 116.8 +/- 23.1% in travelling acoustic waves. Travelling waves enhanced thrombolysis significantly more (p < 0.0001) than did standing waves.

Guideline for Technical Quality Assurance (TQA) of Ultrasound devices (B-Mode) - Version 1.0 (July 2012)

The Technical Quality Assurance group was initiated by the EFSUMB Board in 2007 and met firstly in 2008 to discuss and evaluate methods and procedures published for performing technical quality assurance for diagnostic ultrasound devices. It is the aim of this group of experts to advise the EFSUMB Board of effective and efficacious methods for routine use and to make recommendations regarding the technical aspects of EFSUMB by-law 9, parts 11.6. & 11.7. The groups work focused on new developments and related European projects to establish a common guideline. There is a great need of a well established protocol and dedicated processing software for the performance testing of medical ultrasound equipment. The measurements should be user independent as much as physically possible. Only if these goals are achieved in an international (firstly European) context, the optimal quality of ultrasound imaging can be offered and maintained to the medical community. This guideline aims to offer and summarize suitable procedures and evaluation processes to lend support for an optimal Technical Quality Assurance (TQA) scheme. The content of this guideline was presented to the EFSUMB Board of Directors (delegates) and approved by the EFSUMB Executive Board (ExB) at the regular meeting during EUROSON 2012 in Madrid April 2012.

Amplitude-coded color Doppler: clinical applications

Abstract. Amplitude-coded color Doppler sonography (ACD) has become an useful adjunct to gray-scale US and conventional color Doppler sonography (CD) for the assessment of vascular diseases and pathologic conditions that might affect or alter tissue vascularization or perfusion. Basically, all US units that generate conventional color Doppler information through autocorrelation technique are capable of displaying ACD. This technique is also referred to as power Doppler, amplitude-mode color Doppler US, color Doppler energy (CDE), or US angiography. Amplitude-coded color Doppler sonography has already emerged as a valuable adjunct to conventional CD, particularly for evaluating flow in parts of the body where CD signal is weak because of slow flow, small blood vessels, or both.

Amplitude-coded colour Doppler sonography: physical principles and technique

Abstract. The purpose of this review is to help in understanding the principles of a new ultrasound Doppler technique called amplitude-coded colour Doppler (power) mode. All pertinent information available in the literature on the physical principles of this technique has been revised in order to give a detailed survey. The main components and the key characteristics of this mode are discussed together with illustrative examples. In addition, work-in-progress developments and other future aspects of US imaging in combination with this technique are discussed.

[Ultrasound contrast agents--physical basics].

ZusammenfassungDas Wirkungsprinzip von Ultraschallkontrastmitteln (US-KM, US Ultraschall) beruht auf den speziellen physikalischen und akustischen Eigenschaften der gasgefüllten Mikrobläschen. Abhängig vom Druck der eingestrahlten US-Welle treten neben einer Erhöhung der Rückstreuung, die wesentlich zur Verbesserung der Bildqualität beiträgt, nichtlineare Effekte auf, die von der Erzeugung harmonischer Frequenzanteile bis hin zur Zerstörung der Bläschen durch die Schallwelle reichen. Speziell die nichtlinearen Effekte bilden die Grundlage für neu entwickelte kontrastmittelspezifische Bildgebungstechniken wie harmonic oder intermittent imaging.Dieser Artikel gibt eine Übersicht über die physikalischen Eigenschaften der Mikrobläschen, ihr akustisches Verhalten im Ultraschallfeld sowie die Ausnutzung der auftretenden Effekte für die Bildgebung. Auf neue Entwicklungen in Richtung gewebespezifischer Kontrastmittel und sich daraus ergebende therapeutische Anwendungsmöglichkeiten wird ebenso wie auf die potenziellen Gefahren durch kontrastmittelinduzierte Bioeffekte und daraus resultierenden Richtlinien für die klinische Anwendung der Kontrastmittel (KM) eingegangen.AbstractThe concept of ultrasound contrast agents (UCA) is based on the inherent physical and acoustical properties of gas-filled microbubbles within an ultrasonic (US) field. Depending on the magnitude of the incident US wave different scattering behavior occurs. While it is linear for low acoustic pressures, increasing it leads to the occurrence of nonlinear effects, such as emission of harmonics. High pressure results in destruction of the bubbles producing a highly nonlinear echo signal. Using these specific acoustic signatures opens new perspectives for the development of bubble-specific imaging techniques such as harmonic or intermittent imaging.This review deals with the physical properties of the gas-filled microbubbles, their behavior within an ultrasonic field, and the use of the bubbles’ acoustic signatures for contrast-specific imaging. Novel applications such as tissue-specific microbubbles, targeted imaging, and therapeutic applications using the bubbles as vehicles for drug or gene delivery are discussed as well as acoustically induced bioeffects and considerations for the safe use of UCA from an acoustic standpoint.

In Vitro Measurement Accuracy of Three‐Dimensional Ultrasound

Objectives: We sought to validate distance and volume measurements in three‐dimensional (3‐D) ultrasound images. Background: Even with the latest equipment, it is not known how accurate 3‐D echocardiographic measurements are. Methods: Six models were imaged in ethanol solution and two within a tissue phantom using a mechanical rotation device rotating in 1° intervals and a real‐time 3‐D scanner. Distance and volume measurements (n = 60) were performed in two‐dimensional (2‐D) and 3‐D images using TomTec and InViVo software. Results: Distance measurements had a mean total error between 1.12% and 2.31% for Acuson (2.5 MHZ, 3 MHZ, and 4 MHZ) and Hewlett Parkard (HP) fusion frequencies h and m, HP fusion harmonic B in the axial, and between 3.5% and 4.9% in the lateral dimension. HP Harmonic A and B, Volumetrics (2.5 MHZ), and HP fusion Harmonic A exhibited significantly higher differences to reality with a mean difference between 5.1% and 8.9% in the axial and between 6.2% and 7.9% in the lateral direction. Axial 2‐D measurements were not different from real dimensions except Volumetrics model 1. In the lateral axis, all imaging modalities were different from reality except the fusion harmonic modus B. Using the HP fusion frequency h and HP fusion Harmonic B‐mode, volume measurements in 3‐D images significantly underestimated reality, while Acusons fundamental frequency 3.5 MHZ was not different from real volumes. Conclusion: Three‐dimensional visualization using different ultrasound settings results in different accuracy.

All-optical highly sensitive akinetic sensor for ultrasound detection and photoacoustic imaging

A novel all-optical akinetic ultrasound sensor, consisting of a rigid, fiber-coupled Fabry-Pérot etalon with a transparent central opening is presented. The sensing principle relies exclusively on the detection of pressure-induced changes of the refractive index in the fluid filling the Fabry-Pérot cavity. This enables resonance-free, inherently linear signal detection over a broad bandwidth. We demonstrate that the sensor achieves a exceptionally low peak noise equivalent pressure (NEP) values of 2 Pa over a 20 MHz measurement bandwidth (without signal averaging), while maintaining a flat frequency response, and a detection bandwidth up to 22.5 MHz (-6 dB). The measured large full field of view of the sensor is 2.7 mm × 1.3 mm and the dynamic range is [Formula: see text] or 63 dB at 20 MHz bandwidth. For different required amplitude ranges the upper amplitude detection limit can be customized from at least 2 kPa to 2 MPa by using cavity mirrors with a lower optical reflectivity. Imaging tests on a resolution target and on biological tissue show the excellent suitability of the akinetic sensor for optical resolution photoacoustic microscopy (OR-PAM) applications.

The effect of dead elements on the accuracy of Doppler ultrasound measurements.

The objective of this study is to investigate the effect of multiple dead elements in an ultrasound probe on the accuracy of Doppler ultrasound measurements. For this work, we used a specially designed ultrasound imaging system, the Ultrasonix Sonix RP, that provides the user with the ability to disable selected elements in the probe. Using fully functional convex, linear, and phased array probes, we established a performance baseline by measuring the parameters of a laminar parabolic flow profile. These same parameters were then measured using probes with 1 to 10 disabled elements. The acquired velocity spectra from the functional probes and the probes with disabled elements were then analyzed to determine the overall Doppler power, maximum flow velocity, and average flow velocity. Color Flow Doppler images were also evaluated in a similar manner. The analysis of the Doppler spectra indicates that the overall Doppler power as well as the detected maximum and average velocities decrease with the increasing number of disabled elements. With multiple disabled elements, decreases in the detected maximum and average velocities greater than 20% were recorded. Similar results were also observed with Color Flow Doppler measurements. Our results confirmed that the degradation of the ultrasound probe through the loss of viable elements will negatively affect the quality of the Doppler-derived diagnostic information. We conclude that the results of Doppler measurements cannot be considered accurate or reliable if there are four or more contiguous dead elements in any given probe.

Excitability of chronic hemiparetic muscles: determination of chronaxie values and strength-duration curves and its implication in functional electrical stimulation

Central nervous system disorders affect the anatomy and physiology of the lower motoneuron. This fact has an impact on the stimulation parameters, especially on the duration of the stimulating impulses, for functional electrical stimulation in chronic hemiparetic patients. The aim of this study was thus to test the excitability and to determine chronaxie values and strength-duration curves of weak wrist and finger extensor muscles and spastic finger and wrist flexor muscles in the hemiparetic arm. Twelve patients with chronic hemiplegia (>6 months after the onset of the cerebral lesion) participated in the study. A constant current stimulator was used. As to chronaxie values no significant differences were found between the extensor muscles (mean /spl plusmn/ SD: 0.44 /spl plusmn/ 0.16 ms) and flexor muscles (mean /spl plusmn/ SD: 0.36 /spl plusmn/ 0.22 ms). A moderate variability was seen for both extensor muscles (0.2-0.8 ms) and flexor muscles (0.1-0.9 ms). These values are well within the normal range determined for innervated muscles. All strength-duration curves were completely normal for each muscle. We conclude that in chronic hemiparetic muscles, impulses of the same duration can be used as in muscles of healthy subjects.