Philip Judy | Harvard Medical School (original) (raw)

Papers by Philip Judy

Perception & Psychophysics

An "extreme-detector" model for detecting spatially uncertain targets in noisy backgrounds -predi... more An "extreme-detector" model for detecting spatially uncertain targets in noisy backgrounds -predicts how both detection and localization abilities are degraded by increasing the number of possible target locations. Experiments 1 and 2 show that the model accurately predicts detection and localization performance in tasks with two, four, and eight locations from d' estimates of the observer's ability to detect the target in a known spatial location. These predictions can be linked to the physical stimuli by combining the extreme-detector model with a "psychophysical" model that specifies how stimulus measures determine the target's detectability in a given location. Single-parameter fits of four such combined models were compared with estimates of detection and localization performance in Experiment 3, which manipulated the target's physical signal-to-noise ratio across various conditions of an eightlocation task.

Medical Imaging 1997: Image Perception, 1997

ABSTRACT Performance accuracy for detecting and localizing small nodules on liver CT images depen... more ABSTRACT Performance accuracy for detecting and localizing small nodules on liver CT images depends on whether an observer is required to find dark nodules or bright nodules on those images. We investigated these asymmetric polarity effects using simulated nodules of varying sizes placed on spiral CT scans of clinical patients acquired with intravenous contrast material, which made blood vessels appear brighter than liver background on the displayed CT images. A concurrent analysis of each observer's detection-rating and scored-localization data estimated separate perceptual effects for the nodules of different sizes, and for locations of the dark or bright hepatic findings that observers regarded as most suspicious on the CT images. The results were consistent with equal visibility for dark and bright nodules of identical size and CT-contrast, and a linear increase in visibility with nodule signal-to-noise ratio for a non-prewhitening matched-filter calculation (NPW-SNR). The substantial lower accuracy for detecting and localizing the bright nodules, compared to the dark nodules, was a polarity effect apparently produced by the non- stationary liver CT backgrounds -- i.e., the presence of stronger confusing signals from the bright hepatic findings on these (contrast-enhanced) CT images than from the dark hepatic findings. Bibtex entry for this abstract Preferred format for this abstract (see Preferences) Find Similar Abstracts: Use: Authors Title Abstract Text Return: Query Results Return items starting with number Query Form Database: Astronomy Physics arXiv e-prints

PURPOSE To test and validate the performance of a CAD system that automatically detects abnormal ... more PURPOSE To test and validate the performance of a CAD system that automatically detects abnormal growth patterns of nodular structures in temporal MDCT scans. METHOD AND MATERIALS Abnormal growth of nodular structures provides important information for lung nodule diagnosis. A CAD system (R2 Technology, Sunnyvale, CA) is designed to automatically compare multiple temporal MDCT chest scans and detect such abnormal growth patterns for nodular structures. The system was evaluated on a set of 40 current-prior pairs of MDCT chest examinations (acquired 1-18 months apart) using 1.0-2.5 mm collimations. Double reading by radiologists on each of the 80 (40x2) exams identified a set of 97 nodules that required intervention or surveillance. The CAD system was deployed to detect nodule candidates showing abnormal growth (30 days < doubling time < 450 days) in this data set. Provided with the additional nodule growth information, a radiologist reviewed each pair of the detected nodule can...

PURPOSE To evaluate the performance of a CAD system that can provide automatic monitoring/managem... more PURPOSE To evaluate the performance of a CAD system that can provide automatic monitoring/management (detection, tracking and measurement) of lung nodules for temporal MDCT scans. METHOD AND MATERIALS A CAD system (R2 Technology, Sunnyvale, CA) is designed to help monitor/manage lung nodules present in temporal MDCT scans. It includes a number of streamlined automatic processing modules: lung nodule detection, nodule correspondence tracking and nodule volume measurement. The system was evaluated using a clinical data set comprised of 40 (including 8 metastatic cases) current-prior pairs of MDCT chest examinations (acquired 1-18 months apart) using 1.0-2.5 mm collimations. Double reading by radiologists identified 88 nodules that were present in both current and prior scans. These nodules were determined to require intervention or surveillance. The CAD system was deployed to study its performance in detecting this set of lung nodules and its success rate in tracking their corresponde...

Medical Physics

Low dose CT for lung densitometry has shown utility in evaluating severity and progression of pul... more Low dose CT for lung densitometry has shown utility in evaluating severity and progression of pulmonary emphysema in patients with chronic obstructive pulmonary disease (COPD). Effort is underway at QIBA to standardize measurement protocols based on published longitudinal studies on non-diseased subjects. The purpose of this report is to assess an important component of the densitometry CT data interpretation: the volume adjustment necessary to reduce the effect of respiration on density. The 15 percentile density scores (Perc 15), defined as a threshold HU containing 15% lowest density in the attenuation histogram of the whole lung, were compiled for 30 subjects obtained from the National Lung Cancer Trial database with baseline and repeat scans one year apart. A model assuming an adapted sponge model, where the relationship between volume (V) and density (rho) is given by m=rhoV^s (Staring et al, Med. Phys. 41, 021905 (2014)). s can be obtained for each subject, and for the entire...

PURPOSE The multi-center COPDGene Study uses CT to quantitatively assess the severity of emphysem... more PURPOSE The multi-center COPDGene Study uses CT to quantitatively assess the severity of emphysema. During the course of the study, the COPDGene QA phantom identified two CT scanners of a similar make and model that showed significant shifts in the measured CT attenuation of air, coincident with manufacturer performed calibration. This prompted further investigation to determine if these CT attenuation shifts were also measurable on study scans acquired during the same period. METHOD AND MATERIALS 48 study scans were obtained within 4 weeks before and after scanner calibration (Scanner X: n=24, Scanner Y: n= 24). The mean CT attenuation of tracheal air was measured before and after the phantom shifts occurred. Tracheal air was chosen because it is a large sample of air inside the human body. Unpaired t-test was used to compare values before and after calibration. RESULTS For Scanner X, the median (± s.d.) phantom air attenuation increased from -1009 ± 8.3 to -999 ± 8.5 after calibra...

Nuclear Instruments and Methods, 1977

C73. LUNG IMAGING: NOVEL METHODOLOGIES AND QUALITY CONTROL, 2011

Medical Imaging 2002: Image Perception, Observer Performance, and Technology Assessment, 2002

ABSTRACT Kundel et al. Suggested the use of circle cues to assist human observers during signal-k... more ABSTRACT Kundel et al. Suggested the use of circle cues to assist human observers during signal-known-exactly (SKE) detection experiments. The circles were bipolar (with concentric black and white rings) and centered on potential locations of simulated masses added to mammographic backgrounds. They used a large circle cue (diameter 6.4 cm) and a background size of 7.7 cm (referred to the initial mammogram). They found significant detection performance improvement compared to the no cue conditions. In our previous experiments, we use mammographic background sizes of 6.1 cm and smaller circles with sizes dependent on lesion size. Our circle sizes were selected to subjectively optimize utility but choices may not have been the best. Also, detectability may also depend on background size. In this work, we present human observer results for detecting a realist mass added to mammographic backgrounds using 30 conditions (all combinations of the mass scaled to 3 sizes, 2 background sizes and 5 circle sizes). Performance did not depend on background size. For the smallest mass size (1 mm, 8 pixels), detectability decreased as circle size increased. There may be an optimum near a circle/mass size ratio of 4. The optimum size ratio for the 4 mm mass was 3. For the 16 mm mass, detectability decreased as steadily as circle size increased. The smallest size ratio used was 1.2.

Medical Imaging 2003: Image Perception, Observer Performance, and Technology Assessment, 2003

ABSTRACT Normal mammographic image backgrounds have approximately isotropic power spectra of the ... more ABSTRACT Normal mammographic image backgrounds have approximately isotropic power spectra of the form, P(f) = K/fβ, where f is radial frequency. The values of the exponent, , range from 1.5 to 3.5 with an average of about 2.8. The ideal observer model predicts that, for signals with certain properties, the log-log contrast-detail (CD) diagram slope, m, is given by: m = 0.5(β-2). Previously, we reported results for detection of a model mass (designer nodule) in filtered noise with an exponent of 3. The model and human and model observer 2AFC detection of a simple signal in filtered noise with exponents from 1.5 to 3.5. Our results are in good agreement with the prediction of the above equation. We will also describe results of 2AFC detection experiments done using "twin" noise background with identical noise realizations in the two backgrounds. We could not replicate the results of Johnson et al. For ‘1/f3 noise, they found a CD slope of 0.59 while we found +0.37.

Medical Imaging 1995: Image Perception, 1995

ABSTRACT The effect of target size and size uncertainty on human observer ability to see disk tar... more ABSTRACT The effect of target size and size uncertainty on human observer ability to see disk targets in uncorrelated noise was measured. disk targets were centered in 64-pixel-radius areas of uncorrelated Gaussian noise. Human observers rated the likelihood that a target was present Size uncertainty was introduced in the target-present stimuli by using disk targets with radii ranging 2 to 33.2 pixels. A constant matched-filter signal-to-noise ration was maintained across the range of disk sizes by adjusting the disk contrast. For this mixed size experiment the observer ratings were analyzed using a multiple-distribution extension of the binormal ROC curve fitting procedure. A control experiment measured observer performance in conditions with target-present stimuli of known-size disks. A third experiment evaluated the influence of noise-area size on performance with known-size disks. An observer detection efficiency index, the square of the ration of d' to SNR, decreased at small and large disk radii. The efficiency index decrease for small disks was less in the control experiment (size- known). Observer efficiency indexes for medium and large disks were not significantly difference for the mixed size experiment and the control experiment. Reducing the noise-area size increased the efficiency for small disks and produced an approximately constant efficiency for the small to medium sized disks. Size uncertainty decreased observer detection performance relative to known-size performance for small disk targets. the observer efficiency index for the small targets was increased when small noise areas are used. This finding suggests that the decreased efficiency index for small targets on large noise areas was caused by increased observer uncertainty of target location.

European Radiology, 2015

Objectives To propose and evaluate a method to reduce variability in emphysema quantification amo... more Objectives To propose and evaluate a method to reduce variability in emphysema quantification among different computed tomography (CT) reconstructions by normalizing CT data reconstructed with varying kernels. Methods We included 369 subjects from the COPDGene study. For each subject, spirometry and a chest CT reconstructed with two kernels were obtained using two different scanners. Normalization was performed by frequency band decomposition with hierarchical unsharp masking to standardize the energy in each band to a reference value. Emphysema scores (ES), the percentage of lung voxels below -950 HU, were computed before and after normalization. Bland-Altman analysis and correlation between ES and spirometry before and after normalization were compared. Two mixed cohorts, containing data from all scanners and kernels, were created to simulate heterogeneous acquisition parameters. Results The average difference in ES between kernels decreased for the scans obtained with both scanners after normalization (7.7± 2.7 to 0.3 ± 0.7; 7.2 ± 3.8 to -0.1 ± 0.5). Correlation coefficients between ES and

Medical Imaging 1996: Image Perception, 1996

ABSTRACT An investigation was performed to evaluate objectively observer's ability to fin... more ABSTRACT An investigation was performed to evaluate objectively observer's ability to find lung nodules on compressed spiral computerized tomographic (CT) images of the chest. A set of 80 images from 13 patients served as backdrops. One simulated nodule of either 3.0, 3.4, 4.0, or 5.0 mm in diameter was inserted into each image. These 80 images were viewed on a computer screen in two formats: compressed with a wavelet transform coder at a compression rate of 40:1, and in the uncompressed 8 bit-per-pixel format, windowed down from the 12 bit-per- pixel originals. The images were presented one at a time in random order, as two conditions of 80 images each. Six observers searched for lung nodules on both the original and compressed formats. The tasks were to locate the nodule in each image, and, using a five category rating scale, to indicate the confidence that the indicated location contained a nodule. The results indicate that all observers detected a higher fraction of nodules in the original images than in the compressed images. Even though the compressed images were described by the observers as unacceptable for clinical use because they contained numerous artifacts, the percentage of 4 and 5 mm nodules found in the compressed images was high. Directions of further research include measurement of detection performance at lower compression rates, identification of compression artifacts that get confused with nodules, and analysis of the confidence ratings.

Medical physics, 2012

The purpose of this study was to detect and analyze anomalies between a large number of computed ... more The purpose of this study was to detect and analyze anomalies between a large number of computed tomography (CT) scanners, tracked over time, utilized to collect human pulmonary CT data for a national multicenter study: chronic obstructive pulmonary disease genetic epidemiology study (COPDGene). A custom designed CT reference standard "Test Object" has been developed to evaluate the relevant differences in CT attenuation between CT scanners in COPDGene. The materials used in the Test Object to assess CT scanner accuracy and precision included lung equivalent foam (-856 HU), internal air (-1000 HU), water (0 HU), and acrylic (120 HU). Nineteen examples of the Test Object were manufactured. Initially, all Test Objects were scanned on the same CT scanner before the Test Objects were sent to the 20 specific sites and 42 individual CT scanners that were used in the study. The Test Objects were scanned over 17 months while the COPDGene study continued to recruit subjects. A mixe...

Journal of nuclear medicine : official publication, Society of Nuclear Medicine, 2000

Iterative reconstruction of SPECT images has recently become clinically available as an alternati... more Iterative reconstruction of SPECT images has recently become clinically available as an alternative to filtered backprojection (FBP). However, there is conflicting evidence on whether iterative reconstruction, such as with the ordered-subsets expectation maximization (OSEM) algorithm, improves diagnostic performance over FBP. The study objective was to determine if the detection and localization of small lesions in simulated thoracic gallium SPECT images are better with OSEM reconstruction than with FBP, both with and without attenuation correction (AC). Images were simulated using an analytic projector acting on the mathematic cardiac torso computer phantom. Perfect scatter rejection was assumed. Lesion detection accuracy was assessed using localization receiver operating characteristic methodology. The images were read by 5 nuclear medicine physicians. For each reconstruction strategy and for each observer, data were collected in 2 viewing sessions of 100 images. Two-way ANOVA and...