Patrick C. Brennan

Ambient Lighting: Effect of Illumination on Soft-Copy Viewing of Radiographs of the Wrist

OBJECTIVE The aim of the work was to establish optimum ambient light conditions for viewing radiologic images of the wrist on liquid crystal display monitors. MATERIALS AND METHODS Five ambient light levels were investigated: 480, 100, 40, 25, and 7 lux. Seventy-nine experienced radiologists were asked to examine 30 posteroanterior wrist images and decide whether a fracture was present. All images were displayed on liquid crystal display monitors. Receiver operating characteristic analysis was performed, and the numbers of false-positive and false-negative findings were recorded. RESULTS For all the radiologists, greater area under the receiver operating characteristic curve and lower numbers of false-positive and false-negative findings were recorded at 40 and 25 lux compared with 480 and 100 lux. At 7 lux, the results were generally similar to those at 480 and 100 lux. The experience and knowledge of radiologists specializing in imaging of musculoskeletal trauma appeared to compensate in part for inappropriate lighting levels. CONCLUSION Typical office lighting and current recommendations on ambient lighting can reduce diagnostic efficacy compared with lower levels of ambient lighting. If, however, no light other than that of the monitor is used, results are similar to those with excessive levels of lighting. Careful control of ambient lighting is therefore required to ensure that diagnostic accuracy is maximized, particularly for clinicians not expert in interpreting posteroanterior wrist images.

Diagnostic Efficacy of Handheld Devices for Emergency Radiologic Consultation

OBJECTIVE Orthopedic injury and intracranial hemorrhage are commonly encountered in emergency radiology, and accurate and timely diagnosis is important. The purpose of this study was to determine whether the diagnostic accuracy of handheld computing devices is comparable to that of monitors that might be used in emergency teleconsultation. SUBJECTS AND METHODS Two handheld devices, a Dell Axim personal digital assistant (PDA) and an Apple iPod Touch device, were studied. The diagnostic efficacy of each device was tested against that of secondary-class monitors (primary class being clinical workstation display) for each of two image types-posteroanterior wrist radiographs and slices from CT of the brain-yielding four separate observer performance studies. Participants read a bank of 30 wrist or brain images searching for a specific abnormality (distal radial fracture, fresh intracranial bleed) and rated their confidence in their decisions. A total of 168 readings by examining radiologists of the American Board of Radiology were gathered, and the results were subjected to receiver operating characteristics analysis. RESULTS In the PDA brain CT study, the scores of PDA readings were significantly higher than those of monitor readings for all observers (p < or = 0.01) and for radiologists who were not neuroradiology specialists (p < or = 0.05). No statistically significant differences between handheld device and monitor findings were found for the PDA wrist images or in the iPod Touch device studies, although some comparisons approached significance. CONCLUSION Handheld devices show promise in the field of emergency teleconsultation for detection of basic orthopedic injuries and intracranial hemorrhage. Further investigation is warranted.

Digital tomosynthesis: A new future for breast imaging?

The aim of this article is to review the major limitations in current mammography and to describe how these may be addressed by digital breast tomosynthesis (DBT). DBT is a novel imaging technology in which an x-ray fan beam sweeps in an arc across the breast, producing tomographic images and enabling the production of volumetric, three-dimensional (3D) data. It can reduce tissue overlap encountered in conventional two-dimensional (2D) mammography, and thus has the potential to improve detection of breast cancer, reduce the suspicious presentations of normal tissues, and facilitate accurate differentiation of lesion types. This paper reviews the latest studies of this new technology. Issues including diagnostic efficacy, reading time, radiation dose, and level of compression; cost and new innovations are considered.

Efficient Use of Automatic Exposure Control Systems in Computed Tomography Requires Correct Patient Positioning

Background: Image quality and radiation dose to the patient are important factors in computed tomography (CT). To provide constant image quality, tube current modulation (TCM) performed by automatic exposure control (AEC) adjusts the tube current to the patients size and shape. Purpose: To evaluate the effects of patient centering on tube current–time product (mAs) and image noise. Material and Methods: An oval-shaped acrylic phantom was scanned in various off-center positions, at 30-mm intervals within a 500-mm field of view, using three different CT scanners. Acquisition parameters were similar to routine abdomen examinations at each site. The mAs was recorded and noise measured in the images. The correlation of mAs and noise with position was calculated using Pearson correlation. Results: In all three scanners, the mAs delivered by the AEC changed with y-position of the phantom (P<0.001), with correlation values of 0.98 for scanners A and B and −0.98 for scanner C. With x-position, mAs changes were 4.9% or less. As the phantom moved into the y-positions, compared with the iso-center, the mAs varied by up to +70%, −34%, and +56% in scanners A, B, and C, respectively. For scanners A and B, noise in two regions of interest in the lower part of the phantom decreased with elevation, with correlation factors from −0.95 to −0.86 (P<0.02). In the x-direction, significant noise relationships (P<0.005) were only seen in scanner A. Conclusion: This study demonstrates that patient centering markedly affects the efficacy of AEC function and that tube current changes vary between scanners. Tube position when acquiring the scout projection radiograph is decisive for the direction of the mAs change. Off-center patient positions cause errors in tube current modulation that can outweigh the dose reduction gained by AEC use, and image quality is affected.

What effect does mammographic breast density have on lesion detection in digital mammography

Effective detection of breast cancer using mammography is an important public health issue worldwide. Breasts that contain higher levels of fibroglandular compared with fatty tissue increase breast radio-opacity making it more difficult to differentiate between normal and abnormal findings. The higher prevalence of breast cancer amongst women with denser breasts demands the origination of effective solutions to manage this common radiographic appearance. This brief review considers the impact of higher levels of density on cancer detection and the importance of digital technology in possibly reducing the negative effects of increased density.

Breast Surface Radiation Dose During Coronary CT Angiography: Reduction by Breast Displacement and Lead Shielding

OBJECTIVE The purpose of this study was to prospectively evaluate the effect of cranial breast displacement and lead shielding on in vivo breast surface radiation dose in women undergoing coronary CT angiography. SUBJECTS AND METHODS Fifty-four women (mean age, 59.2 ± 9.8 years) prospectively underwent coronary 64-MDCT angiography for evaluation of chest pain. The patients were randomly assigned to a control group (n = 16), breast displacement group (n = 22), or breast displacement plus lead shielding group (n = 16). Thermoluminescent dosimeters (TLDs) were placed superficially on each breast quadrant and the areolar region of both breasts. Breast surface radiation doses, the degree of breast displacement, and coronary image quality were compared between groups. A phantom dose study was conducted to compare breast doses with z-axis positioning on the chest wall. RESULTS A total of 1620 TLD dose measurements were recorded. Compared with control values, the mean breast surface dose was reduced 23% in the breast displacement group (24.3 vs 18.6 mGy, p = 0.015) and 36% in the displacement plus lead shielding group (24.3 vs 15.6 mGy, p = 0.0001). Surface dose reductions were greatest in the upper outer (displacement alone, 66%; displacement plus shielding, 63%), upper inner (65%, 58%), and areolar quadrants (44%, 53%). The smallest surface dose reductions were recorded for A-cup breasts: 7% for the displacement group and 3% for the displacement plus lead group (p = 0.741). Larger reductions in surface dose were recorded for B-cup (25% and 56%, p = 0.273), C-cup (38% and 60%, p = 0.001), and D-cup (31% and 25%, p = 0.095) sizes. Most of the patients (79%) had either good (< 50% of breast above scan range) or excellent (< 75% of breast above the scan range) breast displacement. No significant difference in coronary image quality was detected between groups. The phantom dose study showed that surface TLD measurements were underestimates of absorbed tissue dose by a mean of 9% and that a strong negative correlation exists between the amount of cranial displacement and breast dose. CONCLUSION Use of breast displacement during coronary CTA substantially reduces the radiation dose to the breast surface.

Malignancy Detection in Digital Mammograms: Important Reader Characteristics and Required Case Numbers

RATIONALE AND OBJECTIVES To determine the relationship between heightened levels of reader performance and reader practice in terms of number of cases read and previous experience. MATERIALS AND METHODS A test set of mammograms was developed comprising 50 cases. These cases consisted of 15 abnormals (biopsy proven) and 35 normals (confirmed at subsequent rescreen). Sixty-nine breast image readers reviewed these cases independently and their performance was measured by recording their individual receiver operating characteristic score (area under the curve), sensitivity, and specificity. These measures of performance were then compared to a range of factors relating to the reader such as years of certification and reporting, number of cases read per year, previous experiences, and satisfaction levels. Correlation analyses using Spearman methods were performed along with the Mann-Whitney test to detect differences in performance between specific reader groups. RESULTS Improved reader performance was found for years certified (P = .004), years of experience (P = .0001), and hours reading per week (P = .003) shown by positive statistical significant relationships with Az values (area under receiver operating characteristic curve). Statistical comparisons of Az values scored for individuals who read varying number of cases per year showed that those individuals whose annual mammographic case load was 5000 or more (P = .03) or between 2000 and 4999 (P = .05), had statistically significantly higher scores than those who read less than 1000 cases per year. CONCLUSION The results of this study have shown variations in reader performance relating to parameters of reader practice and experience. Levels of variance are shown and potential acceptance levels for diagnostic efficacy are proposed which may inform policy makers, judicial systems and public debate.

Lumbar spine radiology: analysis of the posteroanterior projection

Abstract. The use of the posteroanterior (PA) technique as a means of dose reduction has been used effectively in radiology departments for chest and abdominal examinations. The aim of this investigation was to establish if the PA lumbar spine projection offers any advantages over the traditional anteroposterior (AP) view in terms of radiation dose and image quality. The contribution of tissue displacement to any dose reduction was also evaluated. The first part of the study involved the use of an anthropological phantom where entrance surface and an internal dose were measured for both the PA and AP projections. Entrance surface doses for both projections were then measured on randomly allocated female patients. Resultant image quality was assessed using CEC quality criteria. Anterior to posterior patient diameter was also recorded. The results demonstrated that with the PA compared with the AP projection, reductions of 38.6 % (p = 0.016) and 38.9 % (p = 0.02) in patient entrance surface dose and internal phantom dose, respectively. No significant differences in image quality were noted between the two projections. Patient diameter decreased by 1.8 cm with the PA view. The authors conclude that tissue displacement is the main factor for the patient dose reduction and recommend employment of the PA procedure for routine lumbar spine examinations.

Noise-reducing algorithms do not necessarily provide superior dose optimisation for hepatic lesion detection with multidetector CT

OBJECTIVE To compare the dose-optimisation potential of a smoothing filtered backprojection (FBP) and a hybrid FBP/iterative algorithm to that of a standard FBP algorithm at three slice thicknesses for hepatic lesion detection with multidetector CT. METHODS A liver phantom containing a 9.5-mm opacity with a density of 10 HU below background was scanned at 125, 100, 75, 50 and 25 mAs. Data were reconstructed with standard FBP (B), smoothing FBP (A) and hybrid FBP/iterative (iDose(4)) algorithms at 5-, 3- and 1-mm collimation. 10 observers marked opacities using a four-point confidence scale. Jackknife alternative free-response receiver operating characteristic figure of merit (FOM), sensitivity and noise were calculated. RESULTS Compared with the 125-mAs/5-mm setting for each algorithm, significant reductions in FOM (p<0.05) and sensitivity (p<0.05) were found for all three algorithms for all exposures at 1-mm thickness and for all slice thicknesses at 25 mAs, with the exception of the 25-mAs/5-mm setting for the B algorithm. Sensitivity was also significantly reduced for all exposures at 3-mm thickness for the A algorithm (p<0.05). Noise for the A and iDose(4) algorithms was approximately 13% and 21% lower, respectively, than for the B algorithm. CONCLUSION Superior performance for hepatic lesion detection was not shown with either a smoothing FBP algorithm or a hybrid FBP/iterative algorithm compared with a standard FBP technique, even though noise reduction with thinner slices was demonstrated with the alternative approaches. ADVANCES IN KNOWLEDGE Reductions in image noise with non-standard CT algorithms do not necessarily translate to an improvement in low-contrast object detection.

Screening mammography: test set data can reasonably describe actual clinical reporting.

PURPOSE To establish the extent to which test set reading can represent actual clinical reporting in screening mammography. MATERIALS AND METHODS Institutional ethics approval was granted, and informed consent was obtained from each participating screen reader. The need for informed consent with respect to the use of patient materials was waived. Two hundred mammographic examinations were selected from examinations reported by 10 individual expert screen readers, resulting in 10 reader-specific test sets. Data generated from actual clinical reports were compared with three test set conditions: clinical test set reading with prior images, laboratory test set reading with prior images, and laboratory test set reading without prior images. A further set of five expert screen readers was asked to interpret a common set of images in two identical test set conditions to establish a baseline for intraobserver variability. Confidence scores (from 1 to 4) were assigned to the respective decisions made by readers. Region-of-interest (ROI) figures of merit (FOMs) and side-specific sensitivity and specificity were described for the actual clinical reporting of each reader-specific test set and were compared with those for the three test set conditions. Agreement between pairs of readings was performed by using the Kendall coefficient of concordance. RESULTS Moderate or acceptable levels of agreement were evident (W = 0.69-0.73, P < .01) when describing group performance between actual clinical reporting and test set conditions that were reasonably close to the established baseline (W = 0.77, P < .01) and were lowest when prior images were excluded. Higher median values for ROI FOMs were demonstrated for the test set conditions than for the actual clinical reporting values; this was possibly linked to changes in sensitivity. CONCLUSION Reasonable levels of agreement between actual clinical reporting and test set conditions can be achieved, although inflated sensitivity may be evident with test set conditions.