Small-organ dynamic imaging system

Dynamic ultrasonic imaging of superficial body organs adds a new dimension to clinical sonographic examinations in that it enables the real-time evaluation of tissue motion and vascular pulsations. A high-frequency (7.2 MHz) linear-array system has been newly developed that generates simultaneous A- and B-mode displays at 60 frames/sec. The instrument produces real-time scan-converted images in standard television format for direct viewing on television (TV) monitors or clinical recording through videotape equipment. Clinical application of this dynamic imaging system has increased the diagnostic capabilities of ultrasound in ophthalmology, radiology, and pediatrics.     

An integrated system for the non-invasive assessment of vessel wall and hemodynamic properties of large arteries by means of ultrasound.

OBJECTIVES: To integrate methods for non-invasive assessment of vessel wall properties (diastolic diameter, distension waveform and intima-media thickness) and hemodynamic properties (blood flow velocity and shear rate distribution) of large arteries by means of dedicated ultrasound signal processing. METHODS: we have developed an arterial laboratory (ART-lab) system. ART-lab consists of software running on a standard personal computer, equipped with a data acquisition card for the acquisition of radio frequency (RF) ultrasound signals obtained with a conventional echo scanner. It operates either (1) off-line or (2) in real-time. Real-time operation is restricted to the assessment of vessel wall properties because of limitations in computational power. RESULTS: This paper provides an overview of ART-lab ultrasound radio frequency data acquisition and dedicated RF-signal processing methods. The capabilities of the system are illustrated with some typical applications. CONCLUSIONS: ART-lab in real-time mode is a useful tool for monitoring arterial vessel wall dynamics, while off-line it can be employed to investigate the elastic vessel wall properties in combination with hemodynamics, such as blood flow velocity and shear rate distribution.     

A comparison of three different filters for speckle reduction of Doppler spectra

This paper is concerned with speckle suppression in Discrete Fourier Transform based Doppler signals by means of digital image processing. The Doppler spectrum is treated as a greyscale image, and three different noise smoothing algorithms are applied to it. These are the Double Window Modified Trimmed Mean filter, which is nonlinear, and Lee's and the directional filter, which are adaptive in the sense that the smoothing performed by them at each point of the image is controlled by a local image measure. In order to evaluate the performance of the filters, they were applied to a variety of regular waveforms obtained from a physiological flow phantom. Ensemble averaging of a large number of unfiltered spectra was used as the "gold standard" in the evaluation, i.e., as the output of an ideal filter which reveals the exact nature of the underlying Doppler spectrum after speckle has been eliminated. Comparison of the "gold standard" with the ensemble averaged filtered data allowed the noise reduction, bias and distortion of the maximum frequency envelope introduced by filtering to be examined. Overall, the best performance was offered by the directional filter whose action was controlled by the combination of the local edge content and the slope of the least-squares-fit line passing through the data points along each particular direction.     

Digital radiography

Advantages of digital radiography: Improved low contrast imaging; Image processing capability (on line or post-processing); Lower radiation dose for certain applications ("Dose variation"); Digital storage and data transfer; Only one exposure for different imaging characteristics; Optimised real-time image, "digital fluoroscopy" (DBR); Shorter examination times (DBR); Advantages for technically complicated exposures (intensive care, superpositions in the chest region, pediatry) (DLR); High dynamic range, which eliminates over or under exposure; Real time image processing and display (DBR). Disadvantages of digital radiography; Lower spatial resolution is limiting fine structure (max. theoretical resolution is 31p/mm for 1000 and app. 5 lp/mm for 2000 pixels image matrix); Spatial resolution depends from image intensifier diameter or screen format; Lower SNR (Signal to Noise Ratio) for reduced dose, increased noise impression for edge enhancement; Information losses for monitor camera (DBR) -hardcopies; Diagnostic capabilities are reduced by noise and low spatial resolution caused by certain applications (mammography).     

Measuring signal processing by analog/digital conversion using personal computers. I: General principles

Sampling rate, quantization noise and the number of channels to be acquired, the main concepts of computerized data acquisition, are discussed as regards their relevance to clinical research. Different setups of analog/digital conversion and signal processing, such as real-time and post-acquisition mode, are contrasted with respect to performance and installation effort. Additionally, continuous analog recording on FM coded tape is presented as a useful tool for software testing, re-evaluation and backup purposes.     

Processing equipment for two-dimensional echocardiographic data

The multiscan principle has been shown to be an important diagnostic technique in echocardiology. Since the direct visualization of moving cross-sections of the heart reveals considerably more information than can be immediately digested, it is foreseen that automation in acquisition, processing and display of the clinical information should result in further simplification of diagnostic routine. This paper describes the development of the processing equipment for ultrasonic data from a multi-element system and illustrates early results in digital process of this data.In the development of computer aided quantitative analysis, direct storage of the multi-element pictures is the only way to avoid major loss of information. The method employs a PDP-11 EI0 computer (16 K words). Real time recording of the moving images on a digital disk utilizes direct memory access. It offers the possibility to store 50 digitized pictures/sec with sixteen intensity levels. This requires a bit rate of 1 Mbit/sec for the system. With the 1,2 megaword (16 bit) disk a maximum storage capacity of 20 sec of multiscan data results. The rectangular display format of the multiscan is well suited for direct conversion to video. With this system image processing and clinical programming are now in progress.     

A new method of encoding and displaying audio Doppler-shift signals: the chromagram

A technique based on chromaticity is described for processing and displaying audio Doppler-shift signals. A chromaticity vector is derived for a fixed time interval (e.g. 5 ms) of the input Doppler signal, which is directly related to the Fourier power spectrum distribution of that signal over that interval. An approximated approach is then described for implementing the above "chromagraphic analysis" in order to meet Doppler ultrasound real-time requirements. A static and dynamic chromagram display format is defined which enables the chromaticity information to be displayed in colour on a digital television monitor.     

Time accuracy of a barcode system for recording resuscitation events: laboratory trials

Barcode systems for recording clinical data from resuscitation attempts offer the prospect of more complete and time-accurate data collection; in addition, collection of data in digital form and the resulting ease of computer processing promises to facilitate data analysis for quality improvement and research. We conducted trials of such a barcode system, recording events during a videotaped, simulated in-hospital resuscitation, with particular attention to time accuracy. METHODS: Nine subjects watched a videotape of a simulated cardiac resuscitation, recording events first with the barcode system and then with a conventional handwritten form. Recorded times were compared to an accurate record of events (gold standard) from the videotape. RESULTS: Mean absolute errors and standard deviations of errors from the gold standard were significantly smaller with the barcode system (P < 0.01 for both). Numbers of event omissions did not differ significantly. CONCLUSION: The barcode system is more accurate than conventional handwritten recording in capturing event times from a simulated resuscitation. The system shows promise as a means to improve time accuracy of resuscitation records.     

A real time programmable digital filter for biomedical signal enhancement incorporating a high-level design interface

A simple but highly integrated digital signal processing system is described for real time filtering of biomedical signals. It includes the necessary processing and communications hardware, the processing code itself and a high-level software interface that enables the user to design and download arbitrary finite impulse response filters to the run-time system. The filter coefficients are calculated using the frequency sampling method. Since the filters are realized using a finite impulse response, no phase distortion is introduced into the processed signals. A unique feature of the design is the manner in which the software and hardware components have been organized as an intelligent system, obviating on the part of the user a detailed knowledge of filter design theory or any abilities in processor architecture and assembly code programming.     

数字化多深度脉冲波超声多普勒系统的设计与实验研究

目的设计一套数字化脉冲波超声多普勒系统,以实现多深度血流频谱分析和显示.方法首先开发了一块PCI接口的数据采集卡,用于采集正交模拟解调后的超声回波信号,然后在PC平台上对数据进行了累加、壁滤波、谱分析等分析处理.结果导管水流测量和人体血流测量两组实验结果验证了算法的正确性,表明在正交模拟解调后对数据进行模数转换,利用数字信号处理的手段对数据分析处理,完全可以替代传统系统中模拟电路构成的距离选通、积分、采样保持和壁滤波等环节.结论相对于传统的模拟血流测量装置,本系统在稳定性和可移植性方面更具有优势,不仅可方便实现多深度的谱分析和显示,还可扩充更多功能.     

Spectrum shaping with a hardware digital filter

Digital filters have certain characteristics which make possible some things that are either difficult or essentially impossible using analog equipment. Among the most useful characteristics are steep transition band slopes and the capability to shape the passband transfer function in great detail. Unlike most digital filters implemented in software, hardware digital filters can be used to filter signals in real-time. Also, they can be designed to provide a linear phase response. They have some disadvantages as well, however, including moderately high cost, the need for supporting equipment, and at the present time, the need for a moderate degree of computer programming and interfacing skill. We have used hardware digital filters in a number of applications. These applications and the relevant filter performance characteristics are described.     

Intraoperative data acquisition for the study of cerebral dysfunction following cardiopulmonary bypass

As a first step in our study to document postoperative cerebral dysfunction, and to determine whether global cerebral blood flow can be implicated in the etiology of this postoperative change, we have assembled a flexible data acquisition system to acquire and record data from four independent sources, three in digital form and one analog.Each of the monitors that we use has a different requirement: One has eight channels of analog output; the other three have RS-232 digital outputs, each with a data stream with different characteristics. The central element of our data collection is a personal computer running the data acquisition and analysis program, LabVIEW for Windows (National Instruments, Austin, TX). All data are processed through separate LabVIEW global variables; the data strings are concatenated and stored on the hard disk in a spreadsheet format for further analysis.We illustrate an intraoperative recording made during cardiopulmonary bypass (CPB) by showing a graph of the mean arterial pressure (MAP), mixed venous oxyhemoglobin saturation recorded from the jugular bulb (JVO₂Sat), and temperature measured from the nasopharynx. A decrease in the MAP after unclamping the aorta is accompanied by a decrease in JVO₂Sat.This work was supported, in part, by a grant to Eric J. Heyer from CPMC Office of Clinical Trials, 630 West 168th Street, New York, NY.     

In vivo potentiostatic studies at the electrode tissue interface: filter properties of the monophasic action potential (Ag/AgCl) electrode in living rat heart

The monophasic action potential (Franz) catheter is regarded as the criterion standard for high fidelity recording of a class of physiological signals. However, its signal modulation characteristics have never been reported. Broadband impedance spectroscopy was performed in perfused living rat heart in a three-electrode potentiostatic configuration to determine the filtering characteristics of the MAP and model Ag/AgCl electrode-tissue interfaces. The filter transfer function H(f) (attenuation [dB] vs log(f) [log(Hz)]) was derived for the frequency range 10 Hz-10(6) Hz. As a filter, the MAP interface is characterized by two ranges of filtering behavior. At high frequency the MAP interface is a high-pass filter with passband frequency 54 kHz-549 kHz (median 321 kHz) and with -3 dB cutoff points ranging from 10 kHz to 302 kHz. In this high frequency range the transfer function is characterized by decreasing attenuation per decade. However, in the lower frequency range relevant to physiological signals (the monophasic action potential, 0.1-40 Hz), it is a severely attenuating nondiodic high-pass filter element with an average attenuation of 16.87 dB relative to passband. In this physiological range, rolloff is nonlinear with increasing attenuation per decade. While the MAP electrode and model Ag/AgCl electrodes are high-pass filters with robust transfer functions for high frequency signals in the living heart, the attenuation of signals in a frequency range relevant to in vivo physiological recording imparts extreme attenuation that may distort physiological signals unpredictably. This disadvantage may be mitigated by amplitude scaling to a calibrated pure tone signal within the physiological frequency band to recover a reproducible signal.     

Simplifying Pacemaker Follow-up by the Implementation of the NASPE Standards on Computer Interface

One of the basic limitations for the development and use of more sophisticated pacemakers is the difficulty to provide adequate instrumentation and methodology for the follow-up in the clinical environment. To address this problem, the NASPE (North American Society of Pacing and Electrophysiology) Computer Committee has developed an interface standard to allow communication with the pacemaker programmer through many computer systems. The document recommends the use of the RS 232/c (CCITT V.24) interface with baud rates variable from 300 to 19,200, 7 bit word, no parity and Xon/Xoff protocol. The actual message format consists of an SOH code, a function code describing the action to he taken, a variable code defining the parameter on which the action is to be taken, and the actual numerical data. The CHECKSUM is calculated by summing all the ASCII codes beginning after the SOH code and ending with the last byte preceding the checksum itself. The last seven bits so calculated are attached to the message, and a consecutive ETX code ends the communication. At the receiving end, the checksum is recalculated and compared to the value received. If the two match, the message is accepted. Using this format, compatible computer software and pacemaker programmers can be developed independently and function as a unit. The protocol is capable of real-time ECG transmission.     

The Kodak approach to digital cardiovascular imaging laboratories

Cine film had been a global standard in the cardiac catheterization lab for the acquisition, archive, review and exchange for decades. The advent of digital imaging in the cath lab heightened the desire to store cath procedure images in a digital format. The issues related to the development of a digital exchange standard, the data capacities and data rates, lossless and lossy compression, and techniques to obtain digital image data from the lab are discussed. In addition, Kodak's approach to cine film replacement with digital systems is described.     

Digital acquisition and interactive processing of ultrasonic echoes

The requirements for an interactive digital signal processing system for ultrasonic pulse-echo signals are discussed. A system based on an Interdata Model 80 mini-computer and micro-processor interface is described. The system is capable of acquiring ultrasonic data at a sampling rate of 6 MHz. Ultrasonic B-mode data may be acquired in Line Mode, when echo waveform data and transducer position and orientation are stored, or in Section Mode when the data is converted directly into picture form in memory in the same way that a standard echogram is formed on the screen of an oscilloscope. In each case the data for single complete high resolution echogram may be acquired in less than 15 sec. It is shown that the 6 MHz sampling rate is sufficient to faithfully preserve the echo waveshape of a 2 MHz system independently of the relation to the phase of the sampling. Also shown is a cross-sectional echogram of the pregnant uterus, and its digital representation with a raster density of 80 × 100 and 160 × 200 picture elements.The computer is programmed with an interactive program to allow ultrasonic signals to be acquired, stored, processed and examined with the convenience of a desk calculator. Sample operations are illustrated including data interpolation, spectrum analysis, filtering and complex signal deconvolution. The ability of deconvolution techniques to resolve targets separated by less than one wavelength in depth is demonstrated. Possibilities of further processing techniques are outlined.     

Personal digital assistants change management more often than paper texts and foster patient confidence.

INTRODUCTION: Rapid retrieval of information, including drug treatment options, is critical to emergency department practice. OBJECTIVES: To assess feasibility and patient acceptance of personal digital assistants and to determine the scope of management changes. METHODS: Emergency medicine residents (EMRs, n = 18) and emergency medicine attending (EMAs, n = 12) used personal digital assistants with drug database and clinical references. Text versions were also available in the emergency department. We did a prospective, random, cross-over time-motion study, recording retrieval time, source, and changes to patient care for 16 and 8 h for EMRs and EMAs, respectively. We surveyed patients for confidence in EMRs and EMAs with personal digital assistants, and perceived efficiency. RESULTS: EMRs accessed paper (n = 131) or personal digital assistant (n = 181) information on 92.3% of patients (n = 17, both). They accessed personal digital assistant on 61.4% of patients vs. 44.5% with texts (odds ratio 1.99, 95% confidence interval 1.4-2.80). Mean access times were 9.3 and 9.4 s, respectively, +1.4 for both. Personal digital assistant access was 75%/25% between pharmacopeia and clinical resource. Personal digital assistants changed drug choice in 39/181 patients (21.5%), and other management (diagnosis, treatment or disposition) in 15/181 patients (8.3%). Odds ratio for change in management for personal digital assistant vs. paper was 2.00 (95% confidence interval 1.11-3.60). We surveyed patient perception for 198 of 295 patients (67.1%). Fifty percent reported more confidence in their EMRs and EMAs with a personal digital assistant, while 5% reported less confidence. Sixty percent agreed strongly that there is too much medical information to remember. CONCLUSIONS: Personal digital assistants are feasible in an academic emergency department and change management more often than texts. EMRs accessed personal digital assistants more often than paper texts. Patient perceptions of physicians who use personal digital assistants are neutral or favorable.