Subtraction Mode Research Articles

Contrast-enhanced ultrasound with Optison in percutaneous thermoablation of liver tumors

To detect vascularization of liver tumors by ultrasound enhanced with Optison and to determine whether increasing necrosis during a percutaneous thermal ablation can be visualized by this method. Twenty-two patients with non-resectable malignant liver tumors (9 patients with HCC, 13 patients with metastases) and a total number of 34 lesions underwent percutaneous radiofrequency thermoablation using a needle applicator perfused with a 0.9 % NaCl solution (Electrotome HiTT 106, Berchtold). The tumor size ranged from 2 to 8 cm with an average size of 3.6 cm. While intermittent energy was supplied during thermoablation, multi-slice CT (Volume-Zoom, Siemens) and ultrasound were obtained. Ultrasound was performed with a multi-frequency transducer (3 - 7 MHz, LOGIQ 700, GE) and 0.5 to 1 ml of Optison as contrast agent. If necessary, the injection of the contrast agent was repeated after about 30 min. The mechanical index (MI) was set low (0.2 - 0.3) to prevent bubble destruction. Ultrasound power Doppler (PD), contrast harmonic imaging (CHI) and coded harmonic angiography (CHA) as subtraction mode of harmonic imaging were applied intermittently. Only 21 of the 34 lesions showed increased intratumoral perfusion when the conventional B-Mode with PD was used. Similar to spiral CT, the tumor vascularization in the early arterial phase was only reliably visible with CHA after application of contrast agent. CHI with PD was best to detect increasing hypoperfusion of the tumors. When the energy supply was continued, hyperechoic border zones became visible around the central hypoechoic defects. The contrast between remaining tumor and surrounding liver tissue improved in CHI for up to 30 min after the bolus injection of contrast medium, considerably facilitating the evaluation of perfusion. Metal artifacts and the limited amount of contrast agent that can be safely administered interfered with monitoring the thermal ablation with spiral-CT. After an administered energy of maximal 100.000 watts, no more tumor vascularization was seen in 28 of 34 cases. Follow-up spiral-CT showed a complete necrosis in these cases. Evaluating perfusion with contrast-enhanced ultrasound may be helpful in monitoring the evolving necrosis during thermoablation of liver tumors. The more reliable assessment of the tumor necrosis enables a more targeted therapy.

Flash echo gray scale imaging with subtraction in assessment of small hepatocellular carcinoma treated with percutaneous ethanol injection: preliminary report.

To assess the therapeutic effect of percutaneous ethanol injection on small hepatocellular carcinoma by using a flash echo imaging system, a newly developed technique for detecting echoes from microbubble contrast agents more efficiently. Six patients with 7 small nodular hepatocellular carcinomas, proved by fine-needle aspiration cytologic or pathologic examination, were included. Percutaneous ethanol injection was performed until there was no intratumoral color signal on conventional color and power Doppler ultrasonography. A bubble contrast agent was then injected, and flash echo imaging in the subtraction mode was performed for assessment of the therapeutic effect. Dynamic computed tomography, magnetic resonance imaging, and hepatic angiography were also used for evaluation of the therapeutic effect. Five tumors had perfusion defects that were equal in size to or larger than the tumors. No tumor stain was shown on hepatic angiography. Two tumors had partial perfusion defects. Viable tumors were confirmed by tumor resection in 1 case and cytologic examination in the other. Our preliminary results show that flash echo imaging with subtraction has potential value in evaluation of the therapeutic effect of percutaneous ethanol injection on small hepatocellular carcinoma.

Trace determination of mercury by anodic stripping voltammetry at the rotating gold electrode

A simple and highly reliable method for the determination of mercury on a rotating gold disk electrode is reported. The signal is linear with concentration over a wide concentration range (0.2–400nM). The stability of the electrode is excellent. No mechanical polishing between runs is required and a simple electrochemical pretreatment is applied about once in 100runs. The detection limit in synthetic solutions, applying the subtractive mode of anodic stripping voltammetry (SASV) is 50pM for a 120s deposition time at 5000rpm and 4nM in urine sample for 180s deposition time. The reproducibility of the analytical signal is better than 2% in solutions containing 1nMHg(II). The applicability of the method in urine analysis was demonstrated with the use of certified samples. No interference by lead, copper, cadmium, chromium or selenium was found at concentrations corresponding to their toxic occurrence in urine.

VIBRATION ANALYSIS OF ANNULAR PLATES USING MODE SUBTRACTION METHOD

In this paper, a mode subtraction method is presented to investigate the sensitivity of changes in displacement mode shape of annular plates relative to the hole size. It is proved that the displacement modes are sensitive to the presence of a hole in a plate. Jump phenomena are observed in the “residual mode shape”, and the number and locations of peaks are determined based upon the displacement modal analysis. Numerical analyses of the changes in displacement mode shapes for different boundary conditions (C–F, S–F, F–F) and relative hole sizes are given. Experimental tests show good agreement with the numerical results.

Flux measurements of NH 3, N 2O and CO 2 using dual beam FTIR spectroscopy and the flux–gradient technique

We describe the application of a dual beam Fourier transform infrared (FTIR) spectrometer and sampling system for simultaneous measurements of fluxes of several trace gases between the earth's surface and the atmosphere. The spectrometer is based on a commercial dual-output FTIR spectrometer with two long-path absorption cells, fully automated gas handling, data acquisition and quantitative spectrum analysis. The spectrometer may be operated in single or dual beam (optical subtraction) modes; the advantages and disadvantages of the two modes are tested and discussed. Measurements of fluxes of N 2O, CO 2 and NH 3 from agricultural landscapes were made by the flux–gradient technique in two field trials in Sweden and Denmark in 1993. Fluxes of NH 3 were determined following liquid manuring of a young wheat crop in early summer, and N 2O and CO 2 fluxes were measured from a recently harvested wheat stubble on an unfertilised organic soil in late summer. NH 3 fluxes of more than 5 μgN m −2 s −1 (4 kg ha −1 d −1) were measured a day after fertilisation, decreasing to <0.5 μgN m −2 s −1 two days later. N 2O fluxes averaged 42 ngN m −2 s −1 (36 g ha −1 d −1) over the six days of measurement and showed no significant diurnal or longer term variability. Minimum fluxes of 500 and 20 ngN m −2 s −1 for NH 3 and N 2O, respectively, were detectable with 20 min time resolution. The system is readily extendable to CH 4 measurement. Improvement for the future should improve the minimum detectable fluxes.

Contribution of plus and minus end pathways to microtubule turnover.

Turnover is important for the maintenance and remodeling of the cytoskeleton during the processes of cell morphogenesis, mitosis and motility. Microtubule (MT) turnover is thought to occur by dynamic instability, growth and shortening at distal (plus) ends. Recent observation of MT release from the centrosome and depolymerization from proximal (minus) ends indicates the existence of a minus end pathway. To evaluate the relative contributions of plus and minus end pathways to turnover, we analyzed MT dynamics in a model system, the fish melanophore, a large non-motile cell with a regular radial array of long MTs. MT ends were tracked in digital fluorescence time-lapse sequences and life histories of individual MTs were analyzed using random walk theory generalized to the case of diffusion with drift. Analysis of plus end dynamics gave an apparent diffusion coefficient of D=7.5 microm2/minute. The random walk model predicts that the half-time for turnover driven solely by plus end dynamics will depend strongly on position in the cell. Based on the experimentally determined value of D, turnover of MTs near the center of a typical melanophore of radius 70 microm was calculated to require over 5 hours, a paradoxically long time. To examine MT behavior deep in the cytoplasm, we developed a novel, sequential subtraction mode of image analysis. This analysis revealed a subpopulation of MTs which shortened from their minus ends, presumably after constitutive release from the centrosome. Given the relative slowness of plus end dynamics to turn over the root of a long MT, the turnover of MTs near the cell center is determined primarily by the minus-end pathway. MTs released from the centrosome become replaced by newly nucleated ones. The relative contributions of plus and minus end pathways was estimated from the diffusion coefficient, D, for the plus end, the length distribution of MTs, t he frequency of free minus ends, and the rate of minus-end shortening. We conclude that, in large animal cells with a centrosomally focussed array of MTs, turnover occurs by a combination of plus and minus end pathways, the plus end dominating at the cell periphery and the minus end dominating near the cell center.

Detection of low phosphorus contents in neurofilaments of squid axons by Image-EELS contrast spectroscopy.

We show that Image-EELS is suitable for detecting relatively low phosphorus concentrations in very small axoplasmic structures of squid axons. Imaging plates and a CCD camera were used as electron sensors. From image series spanning a certain energy-loss range EELS (electron energy-loss spectra) were derived by averaging read-outs from many axoplasmic particles (APs). The ratio of these spectra to spectra of the background was plotted, showing the contrast modulation as a function of the energy loss. This new approach is called EELC (electron energy-loss-dependent contrast spectroscopy). A distinct phosphorus signal was found in APs of presynaptic terminals of the squid giant synapse, in the peripheral giant axon and, as controls, in ribosomes. Biochemical experiments supported this result. In neurofilament-enriched pellets a phosphorus signal could be directly detected by serial EELS and in electron spectroscopic micrographs. After dephosphorylation of either the pellets or the extruded axoplasm with alkaline phosphatase, phosphorus signals in electron spectroscopic micrographs were absent or much reduced in size and intensity. With Image-EELS inherent limitations of traditional element detection modes in energy filtering transmission electron microscopy can be overcome. Compared with serial EELS, the selective analysis of small areas with irregular shape is possible with greatly improved signal-to-noise ratio. The identification of the element-peak in Image-EEL spectra directly proves the presence of the element within the region of interest. For small peaks, the visualization is facilitated by the contrast presentation (EELC). However, the background subtraction modes used for elemental mapping in electron spectroscopic imaging are subject to uncertainties when elemental ionization edges like the P1,2,3 edge are examined. Imaging plates are very sensitive electron sensors with a wide dynamic range. Unlike photographic emulsions, they allow acquisition of image series covering a large energy-loss range without normalization of exposure times, and direct extraction of EEL spectra. Thus, the combination of Image-EELS and imaging plates is proposed as an efficient new tool for analytical electron microscopy.

MR Angiography with Three-dimensional MR Digital Subtraction Angiography

We have developed a time-resolved, contrast-enhanced, volume-imaging technique for magnetic resonance (MR) angiography, known as three-dimensional (3D) MR digital subtraction angiography (DSA). This technique greatly improves MR angiogram quality because it combines the injection of a contrast agent with the ability to image the temporal passage of this agent and, thereby, obviates the need for timing scans or other complicated synchronization schemes. Three-dimensional MR DSA also represents a potential improvement in the sense that, relative to DSA and computed tomography (CT) angiography, the contrast agent is less toxic. Additionally, unlike CT angiography, images may be acquired during the passage of the contrast agent. Therefore, 3D MR DSA shows the sequential passage of contrast through the arterial and venous system, followed by uptake in various organs. Unlike conventional DSA, 3D MR DSA imaging acquires full volume datasets, which allows subsequent reprojection and reformatting. Because images are obtained at approximately 2-6 s time intervals using a temporal aperture on the order of several seconds, motion (such as respiration) causes only a temporary disruption of image quality, similar to that observed in MR fluoroscopy. These temporal characteristics also make the proposed sequence insensitive to variations in the shape and timing of the contrast-pass curve. Although the individual time-resolved images will have somewhat decreased signal-to-noise ratio (SNR) relative to nontime-resolved scans collected in the same acquisition time, the SNR improvement due to the gadolinium appears to accommodate this trade-off. Additionally, if motion between successive images is small, then the full suite of temporal processing schemes, previously investigated in connection with DSA and time-resolved two-dimensional (2D) MR, such as mask mode subtraction, simple matched filtering and Eigen filtering, can be used to obtain composite images. These derived images generally have an increased SNR or negligible venous signal if an arterial-phase image is not obtained in the early time-resolved images. In summary, 3D MR DSA will significantly advance MR angiography because of the following intrinsic advantages: (1) improved signal-to-noise, (2) scan orientation may be chosen independently of the direction of blood flow, (3) uniform vascular signal, even from regions of complex flow, (4) minimization of motion artifacts, (5) greatly reduced sensitivity to variation in the shape and timing of the contrast bolus, (6) ability to be reformatted or reprojected, and (7) ability to apply a variety of temporal postprocessing techniques.

Quark mass correction to the string potential.

A consistent method for calculating the interquark potential generated by the relativistic string with massive ends is proposed. In this approach the interquark potential in the model of the Nambu--Goto string with point--like masses at its ends is calculated. At first the calculation is done in the one--loop approximation and then the variational estimation is performed. The quark mass correction results in decreasing the critical distance (deconfinement radius). When quark mass decreases the critical distance also decreases. For obtaining a finite result under summation over eigenfrequencies of the Nambu--Goto string with massive ends a suitable mode--by--mode subtraction is proposed. This renormalization procedure proves to be completely unique. In the framework of the developed approach the one--loop interquark potential in the model of the relativistic string with rigidity is also calculated.

Intravenous coronary angiography with synchrotron radiation

Worldwide several systems for Digital Subtraction Angiography in energy subtraction mode (dichromography) with synchrotron radiation are developed. Two of the systems–the system NIKOS in the Hamburger Synchrotronstrahlungslabor HASYLAB in Hamburg and the system in Brookhaven–allow investigations of patients.The aim of the work is to visualize coronary arteries down to 1 mm diameter with an iodine mass density of 1 mg/cm2, thus allowing non-invasive investigations by intravenous application of the contrast medium. The two images for subtraction are simultaneously taken with photon energies just below and above the iodine K-edge (33.17 keV) in a line scan mode.In principle the system NIKOS consists of six main parts:A 20-pole wiggler with a total length of 2.4 m and a field of 1.26 T is installed in the storage ring DORIS at DESY in Hamburg.In a two beam monochromator two bent perfect Si(111) crystals in Laue geometry are used for filtering the quasi-monochromatic beams with a bandwidth of 180 eV out of the white synchrotron radiation beam.In a safety system three independent very fast beam shutters are installed which close within less than 10 ms at any malfunction of the system.Because the line scan mode is used a scanning device moves the patient with up to 50 cm/s through the two monochromatic beams.As a detector a two-line ionization chamber with a spatial resolution of 0.4 mm is installed. The chamber has a dynamic range of 39,000:1 and reads a line within 0.73 ms. The quantum efficiency for 33 keV photons is 85%.The computer system is used for control of the system, data acquisition, image processing and presentation.Since 1990 thirty patients were studied with the system NIKOS. In all cases follow-up investigations after interventions like bypass surgery, angioplasty or rotablation were performed. Intravenous angiograms from investigations with version III of the system are presented.

3.海綿静脈洞近傍の3DCTAngiographyに於けるSubtraction Mode使用の試み

3.海綿静脈洞近傍の3DCTAngiographyに於けるSubtraction Mode使用の試み

Intravenous coronary angiography with synchrotron radiation.

In modern units for coronary angiography, the contrast in the images can be enhanced using digital subtraction angiography (DSA) in temporal subtraction mode (Fig. 1). In this image-processing mode, a number of electrocardiography (ECG-) triggered images are acquired before application of the contrast agent. The mean of these images (i.e., the mask) is subtracted from the images acquired after application of the contrast agent, thus enhancing the vascular structures containing iodine. The resulting images are of high quality, permitting definite luminographic evaluation of the coronary arteries. The images visualize coronary arteries including their bifurcations down to a diameter below 1 mm.

Coronary angiography with synchrotron radiation

Worldwide several systems for Digital Subtraction Angiography in energy subtraction mode (dichromography) are developed. One of the systems which allows investigations of patients ― the system NIKOS in the Hamburger Synchrotronstrahlungslabor HASYLAB at DESY is described. The system consists out of six main parts: The 20 pole wiggler HARWI in the beamline W2 of the storage ring DORIS, the two beam monochromator for the two 12.5 cm wide monochromatic X-ray beams, the safety system, the fast scanning device, the fast low-noise two-line ionization chamber and the computer system. Since 1990 patients were investigated with the system NIKOS. Aim of the work is to visualize coronary arteries down to 1 mm diameter with an iodine mass, density of 1 mg/cm 2 , thus allowing non-invasive investigations by intravenous application of the contrast medium

Analysis of Laryngeal Movement by Digital Subtraction Laryngography

Fine movement of laryngeal components was analyzed by digital subtraction laryngography with the use of a digital fluorography system. Two kinds of image processing modes, the super pulse image subtraction mode and the time interval difference mode, were used for this purpose. By the super pulse image mode, the distance and extent of movement of laryngeal components at vocal initiation and during phonation could be observed. By the time interval difference mode, the amount and direction of motion for a certain interval and fine movement, such as vocal initiation, were determined.

Coronary angiography using synchrotron radiation—Studies in human subjects with the system NIKOS II

Worldwide at many synchrotron radiation laboratories different systems have been developed for digital subtraction angiography (DSA) in energy subtraction mode (dichromography). Aim of the work is to visualize coronary arteries down to 1 mm diameter with an iodine mass density of 1 mg/cm 2, thus allowing non-invasive investigations by intravenous application of the contrast agent. The two images for subtraction are simultaneously taken with photon energies just below and above the iodine K-edge (33.17 keV) in a line scan mode. In the Hamburger Synchrotronstrahlungslabor HASYLAB at DESY the system NIKOS II (NIKOS =Nicht-invasive Koronarangiographie mit Synchrotronstrahlung) consists of six main parts: the 20 pole wiggler HARWI, a two beam monochromator, a safety system, a fast scanning device, a fast low-noise two-line detector, and a computer system. In 1990 the first patients were investigated with the system NIKOS II. 30 ml of contrast medium were injected within 2 s into the vena cava superior. The scan velocity was 9 cm/s corresponding to 5.6 ms per line. The resulting images have a size of 10.0 cm (horizontal) × 12.3 cm (vertical). The pixel size in the images is 0.5 × 0.5 mm 2. The radiation dose per scan (two energy images) was 25 mGy on the average. There are two main problems with the intravenous investigations using DSA in energy subtraction mode for visualization of coronary arteries: • The correct time T from the injection of the contrast material up to the beginning of the scan depends on the individual circulation time of the patient. • In intravenous investigations the small structures of interest (coronary arteries) can be superimposed by large structures (aorta, left atrium and ventricle). The images from the investigations are compared to angiograms, conventionally obtained. They have not yet the quality necessary for clinical routine but show the potential of the method if the system is optimized.

デジタル透影法による発声運動の動的画像解析

Movements of laryngeal components for different vocal attacks were investigated with the use of a digital fluorography (DF) system. In this paper, three kinds of vocal attacks (soft, hard and breathy attack) were compared through subtracted images obtained with TID mode subtraction technique. In the hard attack, the vocal folds during adduction were thicker and the false vocal folds adduction was more marked than in the soft attack. The distention of the subglottal space due to the increase in subglottal presser was larger in the hard attack than in the soft one. In the breathy attack, the vocal folds during adduction were thinner than in the soft attack, and the false vocal folds did not adduct. These findings suggested an existence of a incomplete glottal closure before phonation.

Determination of left ventricular systolic wall thickness by digital subtraction angiography

The accuracy of digital subtraction angiography (DSA) for determination of left ventricular (LV) systolic wall thickness and muscle mass was evaluated in 20 patients (mean age 50 +/- 11 years). Conventional LV angiograms were digitized and subtracted using a combined subtraction mode ('mask mode' and 'time interval difference' subtraction). Wall thickness and muscle mass were determined at end-diastole, after the first- and second-third of systole and at end-systole. M-mode echocardiography (Echo), which was obtained from beam selection of the two-dimensional echocardiogram and conventional angiography (LVA), served as reference techniques. Angiographic LV wall thickness and muscle mass were determined according to the technique of Rackley in both, right (RAO) and left (LAO) anterior oblique projections, whereas echocardiographic wall thickness was measured just below the mitral valve orthogonal to the posterior wall (= LAO equivalent). Percent wall thickening was calculated in all patients. LV end-diastolic wall thickness and muscle mass correlated well between DSA and LVA (LV end-diastolic wall thickness in LAO projection r = 0.72, biplane LV end-diastolic muscle mass r = 0.83), LV end-systolic wall thickness (1.44 vs 1.33 cm, P less than 0.05) and percent wall thickening (52 vs 42%, P less than 0.05) compared favourably between echocardiography and DSA but was significantly larger when echocardiographically measured than with DSA (LAO projection). DSA and echocardiography showed a good correlation in regard to LV end-diastolic and end-systolic wall thickness (correlation coefficient r = 0.89, standard error of estimate SEE = 0.15 cm or 13% of the mean value).(ABSTRACT TRUNCATED AT 250 WORDS)

Arithmetical Teaching.—(I.)

Numeral labeled indicator lamps are sequentially illuminated and extinguished on a panel to display addition or subtraction operation. The quantity added or subtracted is selected by a pulse transmitting dialing machine. A reversing switch controls the direction in which the pulse advances a step switch to sequentially operate the indicator lamp in an addition or subtraction mode.

Comparison of three different principles in the assessment of coronary flow reserve from digital angiograms

In 70 patients without coronary disease we have compared three different principles to assess coronary flow reserve during diagnostic heart catheterization. Digital angiograms with ECG-triggered bolus injections of 4 to 8 ml of contrast medium at rest and after stimulation by dipyridamole (0,5 mg/kg i.v.) or papaverine (12,5 mg i.c.) were acquired in a 512 x 512 matrix at 8 bit resolution (ADAC 4100) and stored on a digital disk at 25 frames/sec. or 2 frames/cardiac cycle (PPR-mode). Angiograms were processed by cyclic R-wave-gated mask mode subtraction and coronary flow in the LAD area was assessed by three different approaches: 1. A traditional densitometric principle. 2. The 'CMAP' principle. 3. A modification of the Stewart-Hamilton principle comparing the total amount of contrast medium that enters the coronary circulation to the area of the contrast dilution curve in a fixed portion of the LAD. Flow was measured simultaneously during angiography using the thermodilution technique for coronary sinus/great cardiac vein flow. Drug stimulation resulted in an increased coronary blood flow up to five times of resting flow. Regression analysis revealed the following results for the assessment of the coronary flow reserved by digital angiography (y) when compared to thermodilution (x): [table: see text] Method 2 could be improved by replacing the density factor by morphometrically measured proximal LAD volume (y = 0.77x + 0.55; r = 0.78; SEE = +/- 0.43). In conclusion, our data suggest that the Stewart-Hamilton principle may be advantageous over time parameter-dependent approaches in the assessment of coronary flow reserve by digital angiography.

Determination of left ventricular wall thickness and muscle mass by intravenous digital subtractionangiocardiography: validation of the method

Left ventricular (LV) wall thickness and muscle mass are important measures of LV hypertrophy. In 24 patients LV end-diastolic wall thickness and muscle mass were determined (two observers) by digital subtraction angiocardiography (DSA) and conventional LV angiocardiography (LVA). Wall thickness was determined over the anterolateral wall of the left ventricle according to the technique of Rackley (method 1) or by planimetry (method 2). Seventeen patients were studied at rest and seven during dynamic exercise. Wall thickness correlated well between LVA and DSA; the best correlations were obtained by a combined subtraction mode using either method 1 or 2 (method 1, r≥0–80; method2, r≥0. 75). The standard error of estimate of the mean (SEE) was slightly lower for method 2 (≤ 10%) than for method 1 (≤ 13%). DSA significantly overestimated wall thickness by 5–7% with method 1 and underestimated by 12–14% with method 2. Muscle mass correlated well between LVA and DSA; the SEE was ≤ 15% for method 1 and≤ 12% for method 2. Overestimation of muscle mass by DSA was 7–11% with method 1 and underestimation was 13–15% with method 2.It is concluded that LV wall thickness can be determined accurately by DSA with an SEE ranging between 10 and 13%. Determination of LV muscle mass is slightly less accurate and the SEE is slightly larger ranging between 13 to 17%. With method 1, wall thickness and muscle mass were over estimated and with method 2 underestimated.