Mm In Steps Research Articles

Perceptibility curve test for conventional and colour-coded radiographs

A colour scale has been developed as a complement to the grey scale in radiographs. The aim of the present study was to compare colour-coded with conventional black-and-white radiographs in terms of the perceptibility curve test. Twelve digital radiographs were exposed on a test object from low to high exposures and recorded using the DIXI system (Planmeca Oy, Helsinki, Finland). An aluminium test object was used containing ten object details in the form of holes with depths ranging from 0.03 mm to 0.30 mm in steps of 0.03+/-0.01 mm. The new colour scale was used to transform the conventional black-and-white radiographs into colour radiographs by specially designed software. Ten observers were asked to analyse four sets of radiographs, i.e. colour-coded and black-and-white radiographs, and reversed colour-coded and reversed black-and-white radiographs. The object detail having the lowest perceptible contrast in each radiograph was registered for each observer. Perceptibility curves were plotted based on the mean value of observer data. Results from the perceptibility curve test showed that the information in colour-coded radiographs was at least as good as that in black-and-white radiographs. In fact, in the lower exposure range, colour-coded radiographs exhibited better perception than conventional black-and-white radiographs. Radiographs that are colour-coded with the applied colour scale may be used as an alternative to conventional black-and-white radiographs.

Spatially variant changes in lens power during ocular accommodation in a rhesus monkey eye.

This study investigated the changes in ocular aberrations that occur over the entire lens equatorial diameter during accommodation in iridectomized rhesus monkey eyes to understand the nature of accommodative lenticular deformation. Accommodation was centrally stimulated to a range of different response amplitudes (0 D to approximately 11 D), and ocular aberrations were measured with a Shack-Hartmann wavefront sensor in both eyes of one previously iridectomized 10-year-old rhesus monkey. At the highest amplitude in the two eyes, aberrations were analyzed over entrance pupil diameters ranging from 3 to 8 mm in steps of 1 mm. Root mean square error of the total measured aberrations, excluding defocus, increased systematically with increasing accommodation from about 1 to 3.5 microns. Spherical aberration became systematically more negative, and vertical coma increased significantly in magnitude with accommodation. There was a strong accommodative change in power near the center of the lens and little change in power at the periphery. At the highest accommodative state, decreasing the analyzed entrance pupil diameter from 8 to 3 mm considerably reduced the wavefront error. The greater increase in optical power near the central region of the lens, combined with an accommodative pupillary miosis, would serve to maximize accommodative refractive change while maintaining acceptable image quality.

Standardising surface electromyogram recordings for assessment of activity and fatigue in the human upper trapezius muscle.

The objectives of this work were to determine optimal surface electromyogram (EMG) electrode locations, and inter-electrode distance (IED), when assessing activity and fatigue in the human upper trapezius muscle. Surface EMG signals were recorded from the upper trapezius muscle of 11 healthy male subjects using a linear array of 16 surface electrodes. Five arm positions were investigated (arms at the side of the body, 45 degrees and 90 degrees flexion, 45 degrees and 90 degrees abduction). Fatiguing (1 kg hand load held for 3 min) and non-fatiguing (no load, 0.5 kg and 1 kg hand load held for 3 s) contractions were made. The variabilities of the average rectified value, root mean square, mean and median power spectral frequency and slope over time of these parameters as functions of electrode location and IED (from 5 mm over a range of 35 mm in steps of 5 mm) were quantitatively evaluated. A criterion for selecting the optimal electrode position was applied. This criterion indicated an optimal location measured from the acromion (38% of the distance from the lateral edge of acromion to the spine of the seventh cervical vertebra) which was statistically the same for all the EMG descriptors, arm positions and IED investigated. Finally, it was found that both EMG variables and indexes of muscle fatigue depended on IED which should thus be properly standardised. On the basis of the sensitivity of the EMG descriptors to electrode location and cross-talk reduction, an IED of 20 mm is suggested when a global analysis of activity in the upper trapezius muscle is made using a single pair of electrodes. This study emphasises that a surface EMG analysis of the upper trapezius muscle, following a proper placement of the electrodes and selection of IED, can give reliable indications of muscle activity and fatigue. Data on the myoelectric manifestations of muscle fatigue of the upper trapezius muscle are provided for the optimal electrode location.

A high-resolution phantom for MRI

Assessment of spatial resolution is an important step to test the performance of new sequence techniques-especially ultrafast techniques with dedicated k-space trajectories or interpolation algorithms. Measurement of the modulation transfer function (MTF) is a rather difficult procedure, but using suitable resolution phantoms allows a simple visual evaluation of spatial resolution.In contrast to commonly used test objects with a very restricted number of resolution patterns we developed a phantom containing resolution patterns from 0.1 to 1.5 mm in steps of 0.1 mm. One resolution pattern consists of five parallel Plexiglas strips with the distance of the strips being equal to their thickness. Together with a Plexiglas cuboid the resolution patterns are mounted on a Plexiglas plate on the bottom of the cylindrical phantom. An aqueous solution of manganese chloride is used to fill the phantom. High resolution cross sections (pixel size: 50 μm) through the resolution patterns were measured to confirm the correct dimensions of the phantom. To verify the appropriateness of the 0.1 and 0.2 mm stacks micro-CT images with a pixel size of 25 μm were acquired additionally for both patterns. Besides visual inspection evaluation of the profile function of signal intensity across the stacks demonstrates that the resolution patterns are sufficiently correct. T1-weighted SE sequences with slightly different pixel sizes as well as T1- and T2∗- weighted gradient echo sequences were applied to demonstrate some possible applications of this phantom. In conclusion, the proposed phantom is well suited to assess the spatial resolution qualitatively (i.e., visually) and quantitatively over a wide range in steps of 0.1 mm.

Bolt Head Fillet Stress Concentration Factors in Cylindrical Pressure Vessels

Linear three-dimensional finite element analysis (FEA) was performed on bolted pressure vessel joints to determine maximum stresses and stress concentration factors in the bolt head fillet as a result of the prying action. The three-dimensional finite element models consisted of a segment of the flanges containing one bolt, using cyclic symmetry boundary conditions. The flanges were each 20 mm in thickness with 901.7 mm inner diameter. The outer flange diameter was varied from 1021 to 1041 mm in steps of 5 mm. The bolt circle diameter was varied from 960.2 to 980.2 mm in steps of 5 mm. The bolts used were 16-mm-dia metric bolts with standard head and nut thickness. The threads were not modeled. The internal vessel pressure was 0.6895 MPa (100 psi). Stress concentration factors in the bolt head fillet were calculated, and they ranged from 3.34 to 4.80. The maximum stress in the bolt as well as the stress concentration factors in the bolt head fillet increase with an increase in bolt circle diameter for a given outer flange dimension. Keeping the bolt circle diameter constant, bolt stress and stress concentration factors in the bolt head fillet decrease with increase in outer flange diameter. The maximum stresses in the bolt were also calculated according to the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code and the Verein Deutscher Ingenieur (VDI) guidelines and compared to the results observed through finite element analysis. The stresses obtained through FEA were larger than those predicted by the ASME and VDI methods by a factor that ranged between 2.96 to 3.41 (ASME) and 2.76 to 3.63 (VDI).

Effects of sevoflurane on the contractility of ferret ventricular myocardium.

Isotonic and isometric variables of contractility and relaxation of isolated ferret right ventricular papillary muscles were measured before and during exposure to incremental concentrations of sevoflurane (0-4.9% vol/vol) (30 degrees C) (n = 9). In a second group of muscles (n = 8), effects of sevoflurane were compared with those of low [Ca(2+)](o) (0.45-2.25 mM in steps of 0.45 mM). Sevoflurane caused a reversible concentration-dependent decrease in contractility (ED(50) of developed force 4.6+/-0.9% vol/vol). When compared with twitches of equal amplitude in low extracellular Ca(2+) concentration, sevoflurane accelerated both isometric and isotonic relaxation. The myocardial depressant effect of sevoflurane is less than that of isoflurane and results mainly from a decrease of intracellular Ca(2+) availability. The abbreviated isometric relaxation likely reflects a decrease in Ca(2+) sensitivity and the faster isotonic relaxation may reflect a mild stimulation of Ca(2+) uptake by the sarcoplasmic reticulum.

Assessing the image quality of a CCD-based digital intraoral radiography system: application of perceptibility curve test.

The perceptibility curve test is a method for evaluating the psychophysical properties of radiographic systems. The concept of the perceptibility curve is based on the minimum perceptible exposure differences that are recorded by a particular imaging system. The perceptibility curve test was applied to a Charge-Coupled Device (CCD)-based digital intraoral radiography system in this study. A test object was made of a square aluminum block, 28 mm in both height and length and 10 mm in thickness. The test object had ten contrast details in the form of round holes with diameters of 1.5 mm. The depths of the holes ranged from 0.05 mm to 0.5 mm in steps of 0.05 +/- 0.01 mm. An X-ray unit was used that operated in the range of 60 to 90 kVp. Test radiographs were shown to observers in random order. Six observers were asked to rate them regarding the number of spots representing holes that they could perceive. The smallest perceptible difference in gray level on the computer monitor, a 15-inch cathode-ray tube (CRT), was then found. The minimum difference in gray level between a perceptible detail and the background was determined. Dose response functions were employed to determine exposures corresponding to these gray levels. For each case, delta logE as a function of the number of object details was calculated. Finally the reciprocal of all values of (delta logE)min were calculated. The number of details which the observers perceived decreased linearly with decreasing delta logE values. The maximum number of details that observers perceived was eight or nine. The perceptibility curves showed that their peaks shifted slightly with a change of the kVp but that their shapes were similar at different kVp settings.

Non-destructive characterization of plasma-sprayed tungsten and braze-joints for fusion by ultra-sonic examination

Abstract High resolution non-destructive ultra-sonic testing has been applied for the characterization of joints and bul materials. The measurements were carried out with an ultra-sonic inspection system of the type Panametric Multiscan TM equipped with a four axis motorized manipulator for positioning the transducer (actuator/receiver unit). For scanning, the system is operated in pulse-echo mode, the desired penetration depth is adjusted by choosing the corresponding time window when recording the reflected signal. Transducer frequencies 5–100 MHz are available. A very fine resolution is achieved, with 100 MHz voids or pores in copper down to a size of 25 μm can be detectec Presently, objects can be scanned up to a dimension of 500 mm in steps ≥ 10 μm. Data acquisition and post processing is performed on a PC with a 1 GHz sonix digitizer card. By ultra-sonic inspection not only individual defects in fully dense materials, but also regions of higher or irregular porosity, such as in plasma sprayed coatings can be detected. To eliminate interference with the residual porosity, the resolution needed for detection can be selected with the transducer frequency. By the use of a special transducer the Cu tube and braze interface in CFC armored divertor modules of monoblock geometry (‘tube-in-tile’) was examined successfully. For the first time it is possible to inspect in-vessel components for fusion non-destructively from the inside of the coolant channel—befor high heat flux loading, reproducibly and reliably mapping all pores and imperfections down to ∼ 125 μm in size (when using 20 MHz working frequency).

Measurement of the coincidence response of very thin BGO crystals

More than half the 511 keV photons in BGO crystals undergo Compton scattering at least once prior to photoelectric interaction within the detector. In a PET scanner, this can result in mis-positioning of annihilation events. As crystal dimensions are made smaller, the fraction of mis-positioned events increases. We have studied the coincidence aperture function (CAF) of 25 mm/spl times/10 mm BGO crystals with thicknesses varying from 1 mm to 3 mm in steps of 0.5 mm. By sandwiching the active crystal between two other BGO crystals not in contact with the photomultiplier, we have studied the effect of Compton scatter upon CAF. By allowing the annihilation photons to be incident along the 25 mm axis and the 10 mm axis, we have studied the effect of detector depth upon the CAF, with and without Compton scatter. The CAF increases linearly with crystal width, ranging from 1.3 mm crystal. The lines joining the FWHM of the CAFs as a function of crystal width appear to converge indicating that no further improvement in resolution can be achieved by reducing crystal width. The CAFs for 10 mm and 25 mm long crystals without Compton scatter is essentially the same. The presence of neighbouring crystals results in an increase in the CAF which is greater for long crystals compared with short ones of the same width. Using 1 mm wide and 10 mm long crystals sandwiched between two uncoupled BGO crystals, we have achieved spatial resolution of 1.64 mm FWHM for a PMT separation of 34 cm. Recent experiments with PMT separation of 11.5 cm have yielded 1.23 mm FWHM CAF in the same setup. >

The effects of medullary reaming on the torsional strength of the femur

The authors have investigated the effect on the torsional strength of the bone of reaming the medulla of the femur from 12 to 16 mm in steps of 1 mm. Five groups of femurs, with 10 pairs in each, were tested comparatively in torsional loading and the torque required to cause fracture and the angle through which the bone had twisted at fracture were directly recorded for each pair. The results of maximum torque at failure (expressed as a proportion of the same parameter for the unreamed femur) plotted against the ratio of bone shaft diameter to reamed diameter showed a good correlation. The proportional maximum torque was found to range from 0.63 (at 12 mm) to 0.36 (at 16 mm) with a sharp transition between 14 and 15 mm. This drastic reduction was felt to be important for both the surgeon and the patient.

Minimum ignition temperature of a self-raising flour on a standard hot-plate

A hot-plate to the draft specification of the International Electrotechnical Commission (Committee 31H) was constructed and located in a chamber with an air extractor and a transparent door. A commercial self-raising flour was tested to assess the relationship between minimum ignition temperature (MIT) and layer depth (5–40 mm in steps of 5 mm). MIT varied from 311°C for 5 mm to 265°C for 20 mm and to 238°C for 40 mm layers. The results fitted the relationship ln ( δ cT 2 r 2 )= M − ( N T ) , with a correlation coefficient of 0·994 for 4 points above the recommended minimum ratio of sample diameter-to-depth of 5:1 and 0·995 for 8 points above the ratio of 2·5:1. The latter relationship had a slightly flatter slope than the former. The variation in results from the two lines was examined. It is recommended for self-raising flour that more reliable results are obtained from 15 mm layer depth than 5 mm because of the tendency of the latter layers to buckle and crack under test. Relationships between hot plate temperature and (a) time taken for layer to reach plate temperature, (b) maximum temperature generated in sample and (c) percent residue after each test, were obtained for the 15 mm layer at plate temperatures up to 410°C.

Effects of gap size between shaft and fins and of angle of fins on the Müller--Lyer illusion.

Assimilation theory was employed to generate quantitative predictions relating the ingoing Müller--Lyer illusion to both angle of fin and gap between shaft and fin. Gap sizes were varied from zero to 18 mm in steps of 2 mm, and angles of fins were varied from 30 degrees to 180 degrees in steps of 30 degrees. Five subjects adjusted the length of a comparison line to match the apparent length of the shaft at each combination of gap size and angle of fin. It was predicted that the gap necessary for a reversed illusion to occur, and the gap at which the maximal reversed effect occurred, would be inversely related to angle of fins. Empirical functions verified the predictions.

A comparison of conventional and blended display technics in scintiscanning.

Data blending was introduced by Christie and MacIntyre (1, 2) to eliminate statistical fluctuations in the presentation of data obtained in scintillation scanning. Beck (3, 4) pointed out the improvement in perception obtained by eliminating or filtering out the high-frequency “noise” caused by statistical variation. For this he used a recording light spot which simulated the response of the detector collimator at its focal point. On the other hand, the method has been criticized for duplicating the poorest feature of the system, the collimator, and for a resultant loss in resolution (5, 6). We have employed a data-blending technic in our laboratory for the past two years (7). It has appeared to be quite satisfactory and is preferred over conventional methods of recording. We felt it necessary, however, to investigate further the capabilities of the method and compare it with a conventional technic. Methods Two scanners were used in these studies. A 3 × 2-in. crystal detector, Picker Magnascanner, was modified as previously described (7). Its maximum speed is 120 cm per minute, and line spacing varies from 1 to 4 mm. A 5 × 2-in. detector, Ohio-Nuclear scanner, can operate up to 500 cm per minute. Line spacing is limited to four settings of 0.75, 1.5, 3.0, and 6.0 mm. Our own low-energy collimators consisting of 1,045 holes to cover a 3-in. crystal were adapted to both detectors (8). For the studies described in this report, 99mTc was used, the collimators being optimal for the 140-keV gamma emission. The 50 per cent isoresponse diameter of a fine-focus, 1.3-in.-thick collimator, is 0.16 in. (4.1 mm) and of a broad-focus, 0.67-in.-thick collimator, 0.35 in. (8.9 mm). For data-blended recording on the photoscan, gaussian light spots of 5 and 10 mm diameter at the 50 per cent maximum density were used with the fine-focus and broadfocus collimators, respectively. Conventional data-recording was accomplished with various round and rectangular spots. In neither scanner do we use contrast enhancement. No ratemeter time-constant factor affects the data presentation. The scanning parameters were calculated on a basis of count density per unit area for data blending. With conventional data recording, scan speed was calculated according to a desired linear density (counts/cm). Three phantoms were employed. The Picker thyroid phantom has the right lobe at twice the activity of the left lobe, and “cold” nodules of 5 mm in the right upper pole, 9 mm in the left upper pole, and 12 mm in the right lower pole. A “hot” nodule, 12 mm in diameter, is situated in the left lower pole. When the phantom is filled with a low-energy gamma emitter, such as 99mTc, the metallic loading-hole screw in the left lower pole appears as a “cold” defect. A second phantom was constructed to determine the minimum diameter of resolution (Fig. 1). There are three rows of “cold” defects ranging from 2 to 10 mm in steps of 2 mm.