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This investigation sought to determine which collimation factors were most important in providing superior image quality with a three-headed SPECT device. The relationship between sensitivity, resolution and SPECT image quality was studied. Two different sets of parallel-hole collimators were used. The ultrahigh-resolution collimators have higher spatial resolution (8.9 versus 11.0 mm), but only 55% of the sensitivity of the high-resolution collimators. A phantom with hot rods was imaged with both collimator sets. Observers compared images with the ultrahigh-resolution collimators to images of varying counts with the high-resolution collimators and determined which high-resolution images matched the ultrahigh-resolution images in image quality. Eleven patient studies were acquired with both collimator sets for equal time, and observers chose which image set they preferred. Transverse images of brain and liver studies were simulated with varying resolution and counts and subjectively compared. The phantom study indicated that the improvement in resolution led to image quality comparable to increasing the number of counts by a factor of 2.5 to 3.4. The clinical studies showed that the ultrahigh-resolution collimators were preferred in a large majority of the cases. These trends were also seen in the simulation study. These results confirm that higher resolution collimators should be used with multihead SPECT devices. The improvement in resolution more than compensates for the loss in sensitivity, leading to an overall improvement in image quality.
We prospectively analyzed benign asbestos-related pleural and parenchymal abnormalities on high-resolution CT scans and correlated them with clinical diagnoses in 100 asbestos-exposed workers. All subjects had high-resolution CT scans in conjunction with conventional CT at the time of clinical evaluation. To evaluate for asbestosis, we ranked high-resolution CT scans as high, intermediate, or low probability of asbestosis on the basis of the multiplicity and extent of observed parenchymal changes. By linear regression analysis, the most distinctive high-resolution CT features of asbestosis included thickened nondependent interstitial short lines and parenchymal bands. In 45 subjects satisfying clinical criteria of asbestosis, high-resolution CT probability of asbestosis was high in 38 (84%), intermediate in five (11%), and low in two (4%). In 20 (36%) of 55 subjects without clinical asbestosis, parenchymal abnormalities indicative of a high probability of asbestosis were observed on high-resolution CT. High-resolution CT probability scores had a strong positive correlation with chest radiographic profusion scores (p less than .0001) and asbestos-related pleural thickening (p less than .0001). Significant inverse correlations were seen with forced vital capacity (p less than .006) and single-breath diffusing capacity (p less than .03), both functional measures of restrictive interstitial lung disease. Neither clubbing nor rales were sufficiently prevalent to have statistical correlation with high-resolution CT scores. High-resolution CT is sensitive in detecting both pleural and parenchymal abnormalities in the asbestos-exposed subject. Asbestos-related pleural changes are observed more frequently on high-resolution CT than on conventional CT or chest radiography. The probability of asbestosis based on high-resolution CT parenchymal features has a significant correlation with existing clinical determinants of disease, and high-resolution CT can detect abnormality when other methods are not diagnostic.
Expressions are formulated for the prediction of solute migration time and resolution as a function applied voltage and buffer concentration in capillary zone electrophoresis. The resolution equation assumes that solute diffusion is the only operative zone-broadening mechanism. A resolution surface in applied voltage and buffer concentration space is presented featuring isochrones that are used to predict the behavior of resolution under constant analysis time. In the resolution-voltage planes the resolution increases continuously with increasing voltage. At the high-voltage border, the resolution decreases continuously with increasing concentration, however, at the low-voltage border the resolution passes through a shallow maximum as the buffer concentration is increased. At constant analysis time, resolution is optimized by simultaneously increasing the voltage and the buffer concentration. In comparison, this theoretical approach, which predicts resolution from solute migration times only, gives values that are consistently about 40-50% higher than experimentally determined resolution.
With the introduction of fast scan techniques and high field imagers, the ability to achieve very high resolution MR images in reasonable imaging times is now possible. Increased resolution allows for better detection of small, high contrast pathological features, but at some cost. Increasing resolution leads to a nonrecoverable decrease in signal-to-noise ratio per pixel and a loss of low contrast detectability for constant imaging time. This article examines the tradeoffs between image resolution, signal-to-noise ratio, and low contrast detectability in MR imaging. Contrast detail curves are presented for images collected in a constant imaging time, with constant field of view and bandwidth but at different resolutions, and these are compared with theoretical curves. The problem of measuring contrast levels in magnitude images, with different resolutions and receiver attenuation values, is discussed and a definition that accommodates these parameters developed. In addition, a clinical example is shown demonstrating a decrease in soft tissue differentiation with increasing resolution, again for fixed imaging time. The results indicate that moving to high resolution imaging matrices requires consideration be given to the sacrifice in low contrast detectability that occurs. Most importantly, it is shown that filtering a high resolution image to a lower resolution image, through nearest neighbor averaging, does not regain the detectability lost in initially collecting the high resolution image.
This study compares the visualization of otic capsule anatomy by thin-section three-dimensional Fourier transformation (3DFT) MR imaging with that by high-resolution CT. The osseous margins of the otic capsule are delineated by high-resolution CT, while MR displays the soft-tissue structures. Routine two-dimensional Fourier transformation (2DFT) spin-echo MR techniques have been limited by slice thickness and signal to noise. Previous longer TE 3DFT gradient-echo MR images of the otic structures have been degraded by magnetic susceptibility effects, which limit spatial resolution and decrease signal to noise. These effects are especially prevalent in the otic capsule, where small soft-tissue structures interface with surrounding air and bone. We developed a high-resolution 3DFT MR technique to image five normal subjects. MR images were compared with high-resolution CT images of the same subjects. Axial, sagittal, and coronal 3DFT gradient-echo MR images with a short TR/TE and 15 degrees flip angle were acquired on a General Electric 1.5-T Signa unit using a 3-in. circular, receive-only surface coil. Axial, sagittal, and coronal 1.5-mm-thick contiguous high-resolution CT bone-algorithm images were obtained also. There was a high correlation between the MR and CT findings. The 3DFT MR images demonstrated significantly higher spatial resolution and soft-tissue detail than the high-resolution CT images did. For example, the endolymphatic duct was seen on twice the number of consecutive sagittal and axial MR slices. Other soft-tissue otic capsule structures routinely seen on the 3DFT MR images included the entire facial nerve, membranous labyrinth including cochlea, and tensor tympani muscle. This study demonstrates a new high-resolution 3DFT MR technique for visualizing the soft-tissue microstructures of the otic capsule and achieves a level of spatial resolution beyond that possible with high-resolution CT.
The minimum spatial resolution required for a total digital radiology department has yet to be defined. A pilot study designed to provide this information was performed. Abnormal and normal radiographic images of children were digitized and redisplayed on film at spatial resolutions of 5.0, 2.5, 1.25, and 0.625 lp/mm. These resolutions are comparable to a digital display of a 14 X 14 in. chest image having pixel elements of 4096 X 4096, 2048 X 2048, 1024 X 1024, and 512 X 512, respectively. Contrast resolution was maintained at 12 bits or 4096 gray levels. The three phases of data acquisition were (1) the standard analysis of receiver operating characteristics, (2) a checklist evaluation of the "seeability" of important structures, and (3) a comparison of all resolutions and a discernment of usability. Fifteen radiologists participated in the study. On the basis of the pediatric cases used, the results showed that the needed spatial resolution for a total digital radiology department may be around 2.5 lp/mm (2048 X 2048). Checklist data on seeability of structures and comparisons of all resolutions give information on specific changes that are occurring as the resolution is decreased, and, when included with the receiver-operating-characteristic data, they become a major component in developing a resolution standard. The finding that 2.5 lp/mm is the required spatial resolution makes construction of a total digital radiology department possible with present state-of-the-art technology.
We compared a prototype long-bore (LB) high-resolution collimator with a low-energy, general-purpose collimator (LEGP) using 99mTc and 123I. The LB collimator provided a 56% improvement in tomographic resolution (autocorrelation width) over the LEGP for 99mTc; for 123I, the gain was 79%, providing substantially improved contrast for small structures. The sensitivity of the LB collimator, however, is only 32% of that of the LEGP. The imaging tasks to be performed on [123I]IMP brain scans involve localization and discrimination of small, high-contrast brain structures and detection of abnormalities in shape, size, or uptake, rather than simple detection of lesions. Observer performance in such higher-order imaging tasks is known to depend on high spatial resolution, even at the cost of sensitivity. Patient studies confirmed that, for resolution-limited tasks, the increase in resolution outweighs the increased noise due to a loss in sensitivity. When the tomographic resolution of the LB collimator was degraded by smoothing to that of the LEGP, the noise in the LB images was lower than that of the LEGP by a factor of 2.9 for the same imaging time, demonstrating the advantage of high-resolution detectors and a smooth reconstruction filter over low-resolution detectors without smoothing. Therefore, collimators designed for high resolution, even at substantial cost in sensitivity, are expected to yield significant improvements for brain SPECT. Geometric calculations show that commercially available low-energy, high-resolution cast collimators promise to meet these requirements.
From the study of the resolution produced by 156 screen-film combinations at a film density between 1.41 and 1.59, the following conclusions are drawn: 1. Resolution is affected by screens, films, and observers. 2. The effect of screens on resolution is much greater than the effect of films. 3. Screens varied greatly in resolving ability. 4. Films did not differ greatly in resolving ability. 5. Cronex Lightning Plus screen and Radelin super high-speed screen produced the lowest resolution and Cronex detail screen produced the highest resolution. 6. In general, the slower the screen, the higher is the resolution and vice versa. 7. There were two groups of films with significant resolution differences. 8. Films designed to be processed automatically did not differ significantly in their resolving ability when processed manually. 9. There is significant interaction effect of screens and films on resolution. 10. Individual visual resolving ability plays a significant role in measuring resolution.
The resolution of images or density maps produced by electron microscopy and electron crystallography can be objectively defined in terms of the spatial frequency of the highest resolution diffraction spot, or Fourier coefficient, included in the data processing. In practice, this objective definition of resolution is expected to be too optimistic if the amplitudes of the highest resolution structure factors are too weak, if the population of high resolution reflections is too sparse, or if the signal-to-noise ratio of the high resolution data is too low. Calculated examples are presented here which illustrate how the apparent resolution in images of a membrane protein, bacteriorhodopsin, can be reduced from a nominal value of 3.5 A by weak amplitudes, sparse data or high noise levels. These calculations provide concrete examples which can serve as a guide when estimating whether the objective definition of image resolution is likely to correspond to a practical, structurally useful estimate of image resolution.
Visual communication equipments were developed early by radiologists for the transmission of analog signals, whereas today's transmission systems are based on digitization of the radiograph. For teletransmission of dental radiographs, it is essential to assess the diagnostic accuracy of various spatial and gray-scale resolutions. Each of 83 dry mandibles was divided into four regions. By random assignment it was decided for each region whether or not a hole should be drilled. Intraoral radiographs (3 x 4 cm) were performed of each region and interpreted. The radiographs were thereafter recorded by a video camera connected to an IBM-PC. The personal computer held a hardware digitization card defined at a 512 x 512 spatial resolution with the possibility of selecting varying gray-scale resolutions. All radiographs were assessed in resolutions with 256 (8 bit), 128 (7 bit), 64 (6 bit), and 32 (5 bit) shades of gray. In no case was the original radiograph more accurate than the 512 x 512 x 8 resolution. In two of the regions evaluated, the images providing 32 shades of gray were less accurate (percentage of true positives and negatives) than the other resolutions (P less than 0.05) while in one region resolutions of 8 bit depth (256 shades of gray) provided a significantly greater accuracy than did the original radiograph and the other image resolutions (P less than 0.05). This was due to fewer false negative scores and was not followed by an increase in false positive scores. It can be concluded that a 512 x 512 spatial resolution is satisfactory for the detection of bone lesions in digitized intraoral radiographs and that 64 shades of gray provide an equally good diagnostic accuracy as do the original radiograph. This might be relevant when transmission times are of importance.
Measures of frequency resolution were obtained in two population samples. The first sample comprised 1764 subjects with various degrees of sensorineural hearing impairment aged from 17 to 80 years. The second sample included 229 subjects with ages between 50 and 75 years, balanced to avoid confounding the effects of impairment and age. Subjects in the second sample were also assessed using a gap-detection measure of temporal resolution and a test of speech identification using sentences in noise. In both samples, frequency resolution ability declined progressively with increasing hearing threshold level (HTL). After accounting for the effects of HTL, there was a minor dependence of frequency resolution on age, older subjects having poorer frequency resolution. Temporal resolution deteriorated with HTL but not with age. The speech identification scores could be predicted from HTL at 2 and 8 kHz and age. Frequency resolution was not a factor. Temporal resolution was only a factor when subjects with extremely poor temporal resolution were included.
We evaluated the requirements on spatial resolution of digital imaging equipment in the cardiac catheterization laboratory. Fifty cinefilms of the heart as the biological object and one film of a lead-ladder-pattern as an objective test were used. The patient films were examined for the visibility of the left ventricular angiogram, coronary arterial tree, coronary artery lesions, branching of septal arteries and the number of septal arteries. All films were viewed three times: with a 625 line TV-system, with a 1249 line TV-system and with a cineprojector. It was found that two application areas with different demands on the spatial and temporal resolution can be distinguished: 1) low spatial resolution and high temporal resolution, e.g. left ventriculography; and 2) high spatial resolution and low temporal resolution, e.g. coronary arteriography. For the diagnostic assessment of the state of the coronary system, the spatial resolution provided by the 1249 line TV-system was sufficient. Exceeding this resolution by using cinefilm quality provided no additional diagnostic information. A frame rate lower than 50 frames per second for coronary arteriography seems possible.
Two clinical experiments were conducted to study the effect of kVp and mAs on resolution and on image contrast percentage. The resolution was measured with a "test pattern." By using a transmission densitometer, image contrast percentage was determined by a mathematical formula. In the first part of the experiment, the density of the film was kept constant by changing the kVp and mAs. In the second part of the experiment, different mAs's were chosen, and for each mAs, several kVp's were used. Five observers read the radiographs. The first experiment showed that, when the film density is kept constant, the higher the kVp, the lower the resolution and image contrast percentage; also, the higher the mAs, the higher the resolution and image contrast percentage. The second experiment showed that when the film density is not kept constant, the correlation between kVp and resolution and between kVp and image contrast percentage was the same as in the first experiment. However, there was negligible correlation between mAs and resolution and between mAs and image contrast percentage. A high positive correlation was found between resolution and image contrast percentage, but a high negative correlation was found between resolution and film density.
According to elementary theory, the resolution of an ultrasonic imaging system increases with the ultrasonic frequency. However, frequency is limited by frequency-dependent attenuation. For imaging at any required depth, resolution improvement beyond the limit imposed by ultrasonic frequency can be obtained by increasing the ultrasonic intensity. This is itself, however, dependent on safety considerations and the effects of nonlinearity. In homogeneous media, image resolution increases with decreasing f-number. Particularly at low f-numbers, however, tissue inhomogeneity leads to a deterioration in image quality. Inhomogeneity may also be considered in terms of phase aberration. It has been found that for a given aperture, image degradation due to phase aberration is worse at higher frequencies. Schemes have been proposed for correction of this problem, but so far model systems do not lend themselves to clinical application. Deconvolution is unsatisfactory, speed correction is impracticable and synthetic aperture scanning and holography are virtually useless in biological tissues. Ultrasound-computed tomography has had only limited success. Speckle reduction can improve target detectability, but at the expense of resolution. Time-frequency control provides a useful partial solution to the problem of resolution reduction resulting from attenuation. It is clear that improved resolution would result in significant clinical benefits. An optimisation system for aperture size and ultrasonic frequency is proposed with signal averaging for resolution enhancement of a defined object area. This would have a compact ultrasonic beam and would allow frame rate to be traded for resolution, by means of signal averaging.