Early detection of breast cancers affects the 5-year recurrence rates and treatment options for diagnosed patients, and consequently, many countries have instituted nationwide screening programs. This study compared the performance of expert radiologists from Australia and the United States in detection of breast cancer. Forty-one radiologists, 21 from Australia and 20 from the United States, reviewed 30 mammographic cases containing two-view mammograms. Twenty cases had abnormal findings and 10 cases had normal findings. Radiologists were asked to locate malignancies and assign a level of confidence. A jackknife free-response receiver operating characteristic, figure of merit (JAFROC, FOM), inferred receiver operating characteristic, area under curve (ROC, AUC), specificity, sensitivity, and location sensitivity were calculated using Ziltron software and JAFROC v4.1. A Mann-Whitney U test was used to compare the performance of Australian and U.S. radiologists. The results showed that when experience and the number of mammograms read per year were taken into account, the Australian radiologists sampled showed significantly higher sensitivity and location sensitivity (p≤0.001). JAFROC (FOM) and inferred ROC (AUC) analysis showed no difference between the overall performance of the two countries. ROC (AUC) and location sensitivity were higher for the Australian radiologists who read the most cases per year.
Purpose: To evaluate the role of radiographic details in global impression of chest x-ray images viewed by experts in thoracic and non-thoracic domains. Materials and Methods: The study was approved by IRB. Five thoracic and five non-thoracic radiologists participated in two tachistoscopic (one low pass and one with the entire frequency spectrum, each lasting 270 ms) each containing 50 PA chest radiographs with 50% prevalence of pulmonary nodule. Eye movements were monitored in order to evaluate a pre-saccade shift of visual attention, saccade latency, decision time and the time to first fixation on a pulmonary nodule. Results: Thoracic radiologists showed significantly higher pre-saccadic shift of visual attention towards pulmonary nodules once using the full frequency spectrum (p < 0.05). An initial saccade orientation made by these radiologists on full resolution images correlated at significant level with their confidence ranking of pulmonary nodules (ρ = -0.387, p < 0.001). Conclusions: Thoracic radiologists benefited from high spatial frequency appearance during a rapid presentation of chest radiograph by allocating pre-saccade attention towards pulmonary nodules. This behavior correlated with a higher number of correct decisions, followed by higher confidence in the decisions made, and briefer reaction times.
The aim of current work was to compare the performance of radiologists that read a higher number of cases to those that read a lower number, as well as examine the effect of number of years of experience on performance. This study compares Australian and USA radiologist with differing levels of experience when reading mammograms. Thirty mammographic cases were presented to 41 radiologists, 21 from Australia and 20 from the USA. Readers were asked to locate and visualize cancer and assign a mark-rating pair with confidence levels from 1 to 5. A jackknife free-response receiver operating characteristic (JAFROC), inferred receiver operating characteristic (ROC), sensitivity, specificity and location sensitivity were calculated. A Mann-Whitney test was used to compare the performance of Australian and USA radiologists using SPSS software. The results showed that the USA radiologists sampled had more years of experience (p≤0.01) but read less mammograms per year (p≤0.03). Significantly higher sensitivity and location sensitivity (p≤ 0.001) were found for the Australia radiologists when experience and the number of mammograms read per year were taken into account. There were no differences between the two countries in overall performance measured by JAFROC and inferred ROC. For the most experienced radiologists within the Australian sample experienced ROC and location sensitivity were higher when compared to the least experienced. The increased number of years experience of the USA radiologists did not result in an increase in any performance metrics. The number of cases per year is a better predictor of improved diagnostic performance.
The performance of a group of 16 American (US) breast screening radiologists in interpreting a number of cases from a recent PERFORMS self-assessment case set which had been carefully selected to exclude small calcifications, using sub-mammographic resolution displays, as compared to a British (UK) group of radiologists using mammographic displays has previously been reported. It was found that the UK group performed better, detecting more cancers with the US participants correctly recalling less. These results were interpreted as due to differences in the displays employed by each group as well as to routine screening differences between the two countries. This current study extended that work with 11 of these experienced US breast screening radiologists further interpreting 20 new PERFORMS mammographic cases using a suitable mammographic clinical workstation. The PERFORMS cases were selected so as to show a range of normal, benign and abnormal appearances. Data from these radiologists were compared to their earlier performance on different PERFORMS cases and sub-clinical displays. Their data were also compared to recent data of 11 UK radiologists reading the same cases, again on clinical workstations as well as to all UK screeners. Despite using equivalent clinical monitors, data indicate differences between the UK and US groups in recall decisions which is not just a function of the countries’ screening approaches. Lower detection of abnormal cases by the US group was found here and reasons for this are explored.
Eye tracking has been used by many researchers to try to shed light on the perceptual processes involved in medical image perception. Despite a large volume of data having been published regarding radiologist viewing patterns for static images, and more recently for stacked imaging modalities, little has been produced concerning angiographic images, which commonly have substantially different characteristics. A study was performed in which 7 expert radiologists viewed a range of digital subtraction angiograms of the peripheral vascular system. Initial results are presented. The observers were free to control the rate at which they viewed the images. Eye position data was recorded for each participant using Tobii TX300 eyetrackers. Analysis was performed in Tobii Studio software and included qualitative analysis of gaze pattern and analysis of metrics including first and total fixation duration etc. for areas of clinical interest. Early results indicate that experts briefly fixate on lesions but do not dwell in the area, rather continuing to inspect the more distal vascular segments before returning. Some individual variation was noted. Further research is required and ongoing.
KEYWORDS: Mammography, Cancer, Breast imaging, Medical imaging, Radiology, Statistical analysis, Breast cancer, Breast, Picture Archiving and Communication System, Target detection
Purpose : To determine whether a strategy of inserting obvious cancers can improve the detection of subsequent abnormal cases in screening mammography sets. Method : Eight experienced breast imaging radiologists (mammographers) were asked to interpret 40 mammography cases in two sittings and localise any malignancies present. Two differing conditions were presented to participants. In Condition 1, there were 36 normal images interspersed with 4 abnormal cases determined to be of medium to high difficulty. Condition 2 differed in that two normal cases were replaced with two obvious malignant cases. These two obvious cases were placed shortly before two subtle malignancies. In both sittings, participants were told they were viewing a screening mammography set. Results: There was no statistical difference in the location sensitivity between the 2 conditions. There was decreased overall specificity in Condition 2 (p = 0.43). Conclusion: Preliminary findings suggest that the insertion of more easily observed abnormal cases into image sets does not improve performance and may in fact result in lower specificity. Further analysis of participants’ eye-positions, and search strategies may offer some explanation of our findings
A number of different viewing distances are recommended by international agencies, however none with specific reference to radiologist performance. The purpose of this study was to ascertain the extent to which radiologists performance is affected by viewing distance on softcopy skeletal reporting. Eighty dorsi-palmar (DP) wrist radiographs, of which half feature 1 or more fractures, were viewed by seven observers at 2 viewing distances, 30cm and 70cm. Observers rated the images as normal or not on a scale of 1 to 5 and could mark multiple locations on the images when they visualised a fracture. Viewing distance was measured from the centre of the face plate to the outer canthus of the eye. The DBM MRM analysis showed no statistically significant differences between the area under the curve for the two distances (p = 0.482). The JAFROC analysis, however, demonstrated a statistically significantly higher area under the curve with the 30cm viewing distance than with the 70 cm distance (p = 0.035). This suggests that while observers were able to make decisions about whether an image contained a fracture or not equally well at both viewing distances, they may have been less reliable in terms of fracture localisation or detection of multiple fractures. The impact of viewing distance warrants further attention from both clinical and scientific perspectives.
Two groups of experienced radiologists from the UK and the USA read the same set of 40 recent FFDM screening cases
to examine the effects of mammography experience, volume of cases read per year, screening practice and monitor
resolution on performance,. Sixteen American radiologists reported these cases using twin DICOM calibrated monitors
which were half the resolution of the clinical mammographic workstations used by 16 UK radiologists. In terms of
effects of volume of cases read per year, then when the group of American radiologists were split into high and low
volume readers (using 5,000 cases p.a. as a criterion) no difference in any performance measure was found. This may be
partly explained by the fact that they were all were very experienced which may have counteracted any case volume
effect here. Comparing the two groups of radiologists from both countries, then the UK group performed better in terms
of the number of cancers detected although the American group recalled more cases, despite having poorer monitors.
This reflects differences in clinical screening practice between the countries, however differences simply due to the
reporting monitors used cannot be ruled out. Data from the study were also compared to that from all UK screeners who
had read these cases as either soft copy or as mammographic film.
In February 2011 the University of Chicago Medical School distributed iPads to its trainee doctors for use when
reviewing clinical information and images on the ward or clinics. The use of tablet computing devices is becoming
widespread in medicine with Apple™ heralding them as "revolutionary" in medicine. The question arises, just because
it is technical achievable to use iPads for clinical evaluation of images, should we do so? The current work assesses the
diagnostic efficacy of iPads when compared with LCD secondary display monitors for identifying lung nodules on chest
x-rays.
Eight examining radiologists of the American Board of Radiology were involved in the assessment, reading chest images
on both the iPad and the an off-the-shelf LCD monitor. Thirty chest images were shown to each observer, of which 15
had one or more lung nodules. Radiologists were asked to locate the nodules and score how confident they were with
their decision on a scale of 1-5. An ROC and JAFROC analysis was performed and modalities were compared using
DBM MRMC.
The results demonstrate no significant differences in performance between the iPad and the LCD for the ROC AUC
(p<0.075) or JAFROC FOM (p<0.059) for random readers and random cases. Sample size estimation showed that this
result is significant at a power of 0.8 and an effect size of 0.05 for ROC and 0.07 for JAFROC.
This work demonstrates that for the task of identifying pulmonary nodules, the use of the iPad does not significantly
change performance compared to an off-the-shelf LCD.
Aim: This study evaluates the assumption that global impression is created based on low spatial frequency components
of posterior-anterior chest radiographs. Background: Expert radiologists precisely and rapidly allocate visual attention
on pulmonary nodules chest radiographs. Moreover, the most frequent accurate decisions are produced in the shortest
viewing time, thus, the first hundred milliseconds of image perception seems be crucial for correct interpretation.
Medical image perception model assumes that during holistic analysis experts extract information based on low spatial
frequency (SF) components and creates a mental map of suspicious location for further inspection. The global
impression results in flagged regions for detailed inspection with foveal vision. Method: Nine chest experts and nine
non-chest radiologists viewed two sets of randomly ordered chest radiographs under 2 timing conditions: (1) 300ms; (2)
free search in unlimited time. The same radiographic cases of 25 normal and 25 abnormal digitalized chest films
constituted two image sets: low-pass filtered and unfiltered. Subjects were asked to detect nodules and rank confidence
level. MRMC ROC DBM analyses were conducted. Results: Experts had improved ROC AUC while high SF
components are displayed (p=0.03) or while low SF components were viewed under unlimited time (p=0.02) compared
with low SF 300mSec viewings. In contrast, non-chest radiologists showed no significant changes when high SF are
displayed under flash conditions compared with free search or while low SF components were viewed under unlimited
time compared with flash. Conclusion: The current medical image perception model accurately predicted performance
for non-chest radiologists, however chest experts appear to benefit from high SF features during the global impression.
As part of a study to establish whether detection of cranial vault fractures is affected by JPEG 2000 30:1 and 60:1 lossy
compression when compared to JPEG 2000 lossless compression we looked at the effects on confidence ratings 55 CT
images, with three levels of JPEG 2000 compression (lossless, 30:1 & 60:1) were presented to 14 senior radiologists, 12
from the American Board of Radiology and 2 form Australia, 7 of whom were MSK specialists and 7 were
neuroradiologists. 32 Images contained a single skull fracture while 23 were normal. Images were displayed on one
calibrated, secondary LCD, in an ambient lighting of 32.2 lux. Observers were asked to identify the presence or absence
of a fracture and where a fracture was present to locate and rate their confidence in its presence. A jack-knifed alternate
free-response receiver operating characteristic (JAFROC) and a ROC methodology was employed and the DBM MRMC
and ANOVA were used to explore differences between the lossless and lossy compressed images. A significant trend of
increased confidence in true and false positive scores was seen with JPEG2000 Lossy 60:1 compression. An ANOVA on
the mean confidence rating obtained for correct (TP) and incorrect (FP) localization skull fractions demonstrated that this
was a significant difference between lossless and 60:1 [FP, p<0.001; TP, p<0.014] and 30:1 and 60:1 [FP, p<0.014; TP,
p<0.037].
Aim: This study aims to determine the effectiveness of a novel image-processing algorithm for multi-scale enhancement
of chest radiographs to improve detection and localization of real pulmonary nodules. Background: Our wavelet-based
enhancement method interactively adjusts the contrast of medical images extracting the spatial frequency components at different scales, followed by a weighting procedure. This study aims to explore the usefulness of this novel procedure for chest image reporting. Method: Sixteen radiologists viewed 50 PA chest radiographs in order to localize pulmonary
nodules. The databank contains 25 normal and 25 abnormal images, with multi-nodule cases. Subjects were allowed to mark unlimited number of locations followed by ranking confidence of nodule presence according to a 5-level scale. Subjects viewed all cases at least in two out of three conditions: unprocessed, enhanced and with morphing between
these two. MCMR ROC and JAFROC analyses were conducted. Results: No significant differences were found in ROC
AUC values across modalities and specialities. Only localization performance with morphing tool is significantly higher (F(1,8)=13.303, p=0.007) for chest expert (JAFROC FOM=0.6355) from non-chest (JAFROC FOM=0.4675) radiologists. Conclusion: Radiologists specialized in chest image interpretation performed consistently well in localizing pulmonary nodules, whereas non-chest radiologists were suffer from distracting effect of morphing tool.
Objective: The aim of this investigation is to determine the impact of hybrid single photon emission computed
tomography/computed tomography (SPECT/CT) on the detection of parathyroid adenoma.
Materials and methods: 16 patients presented with suspected parathyroid adenoma localised within the neck. All patients
were injected with Tc-99m sestamibi and were scanned with a GE Infinia Hawkeye SPECT/CT. There were six negative
and ten positive confirmed cases. Five expert radiologists specializing in nuclear medicine were asked to report on the 16
planar and SPECT data sets and were then asked to report on the same randomly ordered data sets with the addition of
CT. Receiver operating characteristic (ROC) analysis was performed using the Dorfman-Berbaum-Metz multireadermulticase
methodology and sensitivity and specificity values were generated. A significance level of p ≤ 0.05 was set for
all comparisons.
Results: ROC analysis demonstrated an AUC of 0.64 and 0.69 for SPECT and SPECT/CT respectively (p = 0.31). Mean
sensitivity scores increased from 0.64 to 0.80 (p = 0.17) and specificity scores decreased from 0.57 to 0.40 (p = 0.17)
with the addition of the CT data.
Conclusion: This preliminary investigation suggests that extra CT information may increase lesion detection as well as
false positive rates for SPECT-based investigations of a single parathyroid adenoma. However the difference in
diagnostic efficacy between the two groups was not found to be statistically significant therefore requiring further
investigation. These findings have implications beyond the clinical situation described here.
This study reports an incidental finding from a larger work. It examines the relationship between spatial
resolution and nodule detection for chest radiographs. Twelve examining radiologists with the
American Board of Radiology read thirty chest radiographs in two conditions - full (1500 × 1500
pixel) resolution, and 300 × 300 pixel resolution linearly interpolated to 1500 × 1500 pixels. All
images were surrounded by a 10-pixel sharp grey border to aid in focussing the observer's eye when
viewing the comparatively unsharp interpolated images. Fifteen of the images contained a single
simulated pulmonary nodule. Observers were asked to rate their confidence that a nodule was present
on each radiograph on a scale of 1 (least confidence, certain no lesion is present) to 6 (most confidence,
certain a lesion was present). All other abnormalities were to be ignored. No windowing, levelling or
magnification of the images was permitted and viewing distance was constrained to approximately
70cm. Images were displayed on a 3 megapixel greyscale monitor. Receiver operating characteristic
(ROC) analysis was applied to the results of the readings using the Dorfman-Berbaum-Metz multiplereader,
multiple-case method. No statistically significant differences were found with either readers
and cases treated as random or with cases treated as fixed. Low spatial frequency information appears
to be sufficient for the detection of chest lesion of the type used in this study.
This study aimed to measure the sound levels in Irish x-ray departments. The study then established whether these levels
of noise have an impact on radiologists performance
Noise levels were recorded 10 times within each of 14 environments in 4 hospitals, 11 of which were locations where
radiologic images are judged. Thirty chest images were then presented to 26 senior radiologists, who were asked to
detect up to three nodular lesions within 30 posteroanterior chest x-ray images in the absence and presence of noise at
amplitude demonstrated in the clinical environment.
The results demonstrated that noise amplitudes rarely exceeded that encountered with normal conversation with the
maximum mean value for an image-viewing environment being 56.1 dB. This level of noise had no impact on the ability
of radiologists to identify chest lesions with figure of merits of 0.68, 0.69, and 0.68 with noise and 0.65, 0.68, and 0.67
without noise for chest radiologists, non-chest radiologists, and all radiologists, respectively. the difference in their
performance using the DBM MRMC method was significantly better with noise than in the absence of noise at the 90%
confidence interval (p=0.077). Further studies are required to establish whether other aspects of diagnosis are impaired
such as recall and attention and the effects of more unexpected noise on performance.
Introduction
In order to prevent specular reflections, many monitor faceplates have features such as tiny dimples on their surface to
diffuse ambient light incident on the monitor, however, this "anti-glare" surface may also diffuse the image itself. The
purpose of the study was to determine whether the surface characteristics of monitor faceplates influence the detection of
pulmonary nodules under low and high ambient lighting conditions.
Methods and Materials
Separate observer performance studies were conducted at each of two light levels (<1 lux and >250 lux). Twelve
examining radiologists with the American Board of Radiology participated in the darker condition and eleven in the
brighter condition. All observers read on both smooth "glare" and dimpled "anti-glare" faceplates in a single lighting
condition. A counterbalanced methodology was utilized to minimise memory effects. In each reading, observers were
presented with thirty chest images in random order, of which half contained a single simulated pulmonary nodule. They
were asked to give their confidence that each image did or did not contain a nodule and to mark the suspicious location.
ROC analysis was applied to resultant data.
Results
No statistically significant differences were seen in the trapezoidal area under the ROC curve (AUC), sensitivity,
specificity or average time per case at either light level for chest specialists or radiologists from other specialities.
Conclusion
The characteristics of the faceplate surfaces do not appear to affect detection of pulmonary nodules. Further work into
other image types is being conducted.
We report on the development of a novel software tool for the simulation of chest lesions. This software tool was developed for use in our study to attain optimal ambient lighting conditions for chest radiology. This study involved 61 consultant radiologists from the American Board of Radiology. Because of its success, we intend to use the same tool for future studies. The software has two main functions: the simulation of lesions and retrieval of information for ROC (Receiver Operating Characteristic) and JAFROC (Jack-Knife Free Response ROC) analysis. The simulation layer operates by randomly selecting an image from a bank of reportedly normal chest x-rays. A random location is then generated for each lesion, which is checked against a reference lung-map. If the location is within the lung fields, as derived from the lung-map, a lesion is superimposed. Lesions are also randomly selected from a bank of manually created chest lesion images. A blending algorithm determines which are the best intensity levels for the lesion to sit naturally within the chest x-ray. The same software was used to run a study for all 61 radiologists. A sequence of images is displayed in random order. Half of these images had simulated lesions, ranging from subtle to obvious, and half of the images were normal. The operator then selects locations where he/she thinks lesions exist and grades the lesion accordingly. We have found that this software was very effective in this study and intend to use the same principles for future studies.
Clinical radiological judgments are increasingly being made on softcopy LCD monitors. These monitors are found throughout the hospital environment in radiological reading rooms, outpatient clinics and wards. This means that ambient lighting where clinical judgments from images are made can vary widely. Inappropriate ambient lighting has several deleterious effects: monitor reflections reduce contrast; veiling glare adds brightness; dynamic range and detectability of low contrast objects is limited. Radiological images displayed on LCDs are more sensitive to the impact of inappropriate ambient lighting and with these devices problems described above are often more evident.
The current work aims to provide data on optimum ambient lighting, based on lesions within chest images. The data provided may be used for the establishment of workable ambient lighting standards. Ambient lighting at 30cms from the monitor was set at 480 Lux (office lighting) 100 Lux (WHO recommendations), 40 Lux and <10 Lux. All monitors were calibrated to DICOM part 14 GSDF.
Sixty radiologists were presented with 30 chest images, 15 images having simulated nodular lesions of varying subtlety and size. Lesions were positioned in accordance with typical clinical presentation and were validated radiologically. Each image was presented for 30 seconds and viewers were asked to identify and score any visualized lesion from 1-4 to indicate confidence level of detection. At the end of the session, sensitivity and specificity were calculated. Analysis of the data suggests that visualization of chest lesions is affected by inappropriate lighting with chest radiologists demonstrating greater ambient lighting dependency. JAFROC analyses are currently being performed.
Purpose
The aim of the work is to determine the optimum ambient lighting conditions for viewing softcopy radiological images on LCD.
Materials and Methods
The study measured the diagnostic performance of observers viewing images on liquid crystal display (LCD) monitor under different ambient lighting conditions: 480, 100, 40, 25 and 7lux. An ROC analysis was performed as a measure of diagnostic performance. A set of 30 postero-anterior wrist images was used, 15 of which had fractures present the remainder were normal. These were evaluated by 79 American Board of Radiology certified experienced Radiologists.
Results
The observers performed better at 40 and 25lux compared with 480 and 100 lux. At 7lux, the observers' performance was generally similar to that at 480 and 100lux.
Conclusion
Using the previously recommended ambient lighting levels of 100lux resulted in no improvement over typical office lighting of 480lux. Lower ambient lighting levels ranging from 40-25lux improves diagnostic performance over higher levels. Lowering ambient lighting to 7lux (almost complete darkness apart from the light emanating from the monitor) reduces diagnostic performance to a level equal to that of typical office lighting. It is clearly important to control ambient lighting to ensure that diagnostic performance is maximized.
The goal of this study was to determine what the influence of image processing functions was on decisions and decision changes made while reading chest radiographs displayed on a monitor. Six radiologists read 168 computed radiography chest images first without them with the use of six image processing functions. Diagnostic performance was measured using receiver operating characteristic analysis, and decision changes made without and with processing use were analyzed. Diagnostic performance did not differ statistically for readings without and with image processing. The decision change analysis showed that readers were just as likely to change decisions from true-positive to false-negative as they were from false-negative to true- positive. With image processing, there were significantly more changes from true-negative to false-positive than from false-positive to true-negative. 93 percent of all decisions did not change with the use of image processing. No significant correlations were found between the type of lesions present on the radiography and the type of image processing function sued. Positive decision changes made with the use of image processing are offset by equivalent numbers of negative decision changes. The use of image processing does not affect significantly diagnostic performance in chest radiography.
At the University of Arizona, software development for image viewing tasks use object-oriented techniques for scalability, portability, cost and the ability to adapt rapidly to changing technology. Object orientation facilitates object-based decomposition, rapid development, code reuse and portability. These techniques were used developing software for a diagnostic system for the Pulmonary Section of Toshiba General Hospital, Tokyo, Japan. Object-oriented analysis and design were based on the Grady Booch method. Implemented used visual C++. Software components are implemented as cooperating objects. The resulting Toshiba-Arizona Viewing Station (TAVS) software system was installed in Tokyo in July 1996 for clinical evaluation. The host system provides 1760 X 2140, grey scale resolution. HIS/RIS integration allows HIS/RIS workstations to control the TAVS. TAVS code has been demonstrated on systems ranging from 'palm-top' computers to high-performance desktop systems. TAVS software objects were then modified and a TAVS system was installed in the University Medical Center, Tucson, Arizona supporting diagnostic image viewing tasks in the Emergency Department. This approach has demonstrated support for rapid development and adaptability to diverse end-user requirements and produced software which can operate across platforms.
A review console displaying digital radiographs should automatically display the chest images in proper orientation to save radiologists' time. To accomplish this feat, the authors have developed a simple, rapid algorithm that can be implemented in hardware. Linear regression is used on two orthogonal profiles to determine the top of the image. The edge of the heart is found to make sure the image is not displayed as a mirror image. The algorithm was 90.4 percent successful on 115 chest images.
KEYWORDS: Medical imaging, Fourier transforms, Linear filtering, Algorithm development, Image acquisition, Chest imaging, Radiology, Image processing, Data acquisition, Analog electronics
We frequently encounter digitally stored images whose formatting information, the number of lines and pixels, has been lost. Without the formatting information the image becomes practically inaccessible. Formatting loss can be caused by: (1) Legacy images - they come somewhere from the dim past; (2) Image acquisition devices that do not store the dimensions; (3) The proliferation of storage standards using headers that require software for new formats. In order to use the image, the dimensions must be recovered. We developed a robust method that determines the width and height of images stored in lexicographic order. We constructed an approximately periodic function from contiguous image data. Similar to a periodic function, the auto-correlation function of the contiguous data exhibits peaks spaced with a period that is equal to the width of the images. The height is determined by dividing the file's size by the width. We tested the algorithm on 42 medical images and one aerial photo. We created a larger test base by cropping regions of different sizes from the images and sub- sampling the images into several sizes. The algorithm found the correct dimensions in all cases except one - when the region consisted of periodic data. In this case, the auto- correlation function has peaks due to the periodicity of the data that cannot be discerned form the periodicity of the line lengths since all the peaks of the auto-correlation function are equal. The algorithm cannot discern the correct width among the ambiguous peaks. In practice, periodicity will never happen in real medical images.
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