Mariusz W. Pietrzyk

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.

Quantitative measures confirm the inverse relationship between lesion spiculation and detection of breast masses.

OBJECTIVE To identify specific mammographic appearances that reduce the mammographic detection of breast cancer. MATERIALS AND METHODS This study received institutional board review approval and all readers gave informed consent. A set of 60 mammograms each consisting of craniocaudal and mediolateral oblique projections were presented to 129 mammogram Breastscreen readers. The images consisted of 20 positive cases with single and multicentric masses in 16 and 4 cases, respectively (resulting in a total of 24 cancers), and readers were asked to identify and locate the lesions. Each lesion was then ranked according to a detectability rating (ie, the number of observers who correctly located the lesion divided by the total number of observers), and this was correlated with breast density, lesion size, and various descriptors of lesion shape and texture. RESULTS Negative and positive correlations between lesion detection and density (r = -0.64, P = .007) and size (r = 0.65, P = .005), respectively, were demonstrated. In terms of lesion size and shape, there were significant correlations between the probability of detection and area (r = 0.43, P = .04), perimeter (r = 0.66, P = .0004), lesion elongation (r = 0.49, P = .02), and lesion nonspiculation (r = 0.78, P < .0001). CONCLUSIONS The results of this study have identified specific lesion characteristics associated with shape that may contribute to reduced cancer detection. Mammographic sensitivity may be adversely affected without appropriate attention to spiculation.

The effect of JPEG2000 compression on detection of skull fractures.

RATIONAL AND OBJECTIVES To investigate the effect of the Joint Photographic Experts Group (JPEG2000) 30:1 and 60:1 lossy compression on the detection of cranial vault fractures when compared to JPEG2000 lossless compression. MATERIALS AND METHODS Fifty cranial computed tomography (CT) images were processed with three different level of JPEG2000 compression (lossless, 30:1 lossy, and 60:1 lossy) creating three sets of images. These were presented to five musculoskeletal specialists and five neuroradiologists. Each reader read at two of the three compression levels. Twenty-two cases contained a single fracture; the remaining 28 cases contained no fractures. Observers were asked to identify the presence or absence of a fracture, to locate its site, and rate their degree of confidence. Receiver operating characteristic (ROC), jackknife free-response receiver operating characteristic (JAFROC) and the Dorfman-Berbaum-Metz multiple reader multiple case (DBM-MRMC) analyses were used to explore differences between the lossless and lossy compressed images. RESULTS JPEG2000 lossless and 30:1 lossy compression demonstrated no significant difference in their performance with JAFROC and DBM-MRMC analysis (P < .416); however, JPEG2000 30:1 lossy compression demonstrated significantly better performance than 60:1 lossy compression (P < .016). A significant increase in misplaced confidence ratings was also seen with 60:1 (P < .037) over 30:1 lossy and lossless compression. CONCLUSION JPEG2000 60:1 compression degrades the detection of skull fractures significantly while increasing the confidence with which readers rate fractures compared with 30:1 lossy and lossless compression. JPEG2000 30:1 lossy compression does not significantly change performance when compared to JPEG2000 lossless for the detection of skull fractures on CT.

The impact of mammographic density and lesion location on detection

The aim of this study is to examine the impact of breast density and lesion location on detection. A set of 55 mammographic images (23 abnormal images with 26 lesions and 32 normal images) were examined by 22 expert radiologists. The images were classified by an expert radiologist according to the Synoptic Breast Imaging Report of the National Breast Cancer Centre (NBCC) as having low mammographic density (D1<25% glandular and D2> 25-50% glandular) or high density (D3 51-75% glandular and D4> 75-glandular). The observers freely examined the images and located any malignancy using a 5-point confidence. Performance was defined using the following metrics: sensitivity, location sensitivity, specificity, receiver operating characteristic (ROC Az) curves and jackknife free-response receiver operator characteristics (JAFROC) figures of merit. Significant increases in sensitivity (p= 0.0174) and ROC (p=0.0001) values were noted for the higher density compared with lower density images according to NBCC classification. No differences were seen in radiologists’ performance between lesions within or outside the fibroglandular region. In conclusion, analysis of our data suggests that radiologists scored higher using traditional metrics in higher mammographic density images without any improvement in lesion localisation. Lesion location whether within or outside the fibroglandular region appeared to have no impact on detection abilities suggesting that if a masking effect is present the impact is minimal. Eye-tracking analyses are ongoing.

Classification of radiological errors in chest radiographs, using support vector machine on the spatial frequency features of false- negative and false-positive regions

Aim: To optimize automated classification of radiological errors during lung nodule detection from chest radiographs (CxR) using a support vector machine (SVM) run on the spatial frequency features extracted from the local background of selected regions. Background: The majority of the unreported pulmonary nodules are visually detected but not recognized; shown by the prolonged dwell time values at false-negative regions. Similarly, overestimated nodule locations are capturing substantial amounts of foveal attention. Spatial frequency properties of selected local backgrounds are correlated with human observer responses either in terms of accuracy in indicating abnormality position or in the precision of visual sampling the medical images. Methods: Seven radiologists participated in the eye tracking experiments conducted under conditions of pulmonary nodule detection from a set of 20 postero-anterior CxR. The most dwelled locations have been identified and subjected to spatial frequency (SF) analysis. The image-based features of selected ROI were extracted with un-decimated Wavelet Packet Transform. An analysis of variance was run to select SF features and a SVM schema was implemented to classify False-Negative and False-Positive from all ROI. Results: A relative high overall accuracy was obtained for each individually developed Wavelet-SVM algorithm, with over 90% average correct ratio for errors recognition from all prolonged dwell locations. Conclusion: The preliminary results show that combined eye-tracking and image-based features can be used for automated detection of radiological error with SVM. The work is still in progress and not all analytical procedures have been completed, which might have an effect on the specificity of the algorithm.

Direction of an initial saccade depends on radiological expertise

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.

Assessing the effect of a true-positive recall case in screening mammography: does perceptual priming alter radiologists' performance?

OBJECTIVE To measure the effect of the insertion of less-difficult malignant cases on subsequent breast cancer detection by breast imaging radiologists. METHODS The research comprises two studies. Study 1: 8 radiologists read 2 sets of images each consisting of 40 mammographic cases. Set A contained four abnormal cases, and Set B contained six abnormal cases, including two priming cases (less difficult malignancies) placed at intervals of three and five subsequent cases before a subtle cancer. Study 2: 16 radiologists read a third condition of the same cases, known as Set C, containing six abnormal cases and two priming cases immediately preceding the subtle cancer cases. The readers were asked to localize malignancies and give confidence ratings on decisions. RESULTS Although not significant, a decrease in performance was observed in Set B compared with in Set A. There was a significant increase in the receiver operating characteristic (ROC) area under the curve (z = -2.532; p = 0.0114) and location sensitivity (z = -2.128; p = 0.0333) between the first and second halves of Set A and a marginal improvement in jackknife free-response ROC figure of merit (z = -1.89; p = 0.0587) between the first and second halves of Set B. In Study 2, Set C yielded no significant differences between the two halves of the study. CONCLUSION Overall findings show no evidence that priming with lower difficulty malignant cases affects the detection of higher difficulty cancers; however, performance may decrease with priming. ADVANCES IN KNOWLEDGE This research suggests that inserting additional malignant cases in screening mammography sets as an audit tool may potentially lead to a decrease in performance of experienced breast radiologists.

The impact of using a JAFROC or ROC approach on the conclusions of a typical observer performance study

Purpose: The current study aims to compare ROC with JAFROC methodologies to investigate how the choice of available analytical approaches in observer studies can impact upon study conclusions. Methods and materials: A total of 129 readers independently reviewed 60 mammographic cases, 20 of which were biopsy proven cases (abnormal) and 40 were normal. Each case consisted of the four standard cranio-caudal (CC) and medio-lateral oblique (MLO) projections. Readers were asked to interpret and locate any presence of cancer, and levels of confidence were scored on a scale of 1-5. Radiology workstations supporting 5MP diagnostic monitors and with full image manipulation tools were used to display all images. JAFROC and ROC methodologies were used and figures of merit and Az values respectively were correlated against key reader characteristics such as experience, qualifications, breast reading practices and physical characteristics using Spearman techniques. Results: Correlation analysis between reader characteristics and JAFROC analysis demonstrated that four key characteristics were linked to performance: years of qualification as a radiologist (p=0.05, r= 0.18), years reading mammograms (p=0.01, r=0.24), number of mammograms read per year (p=0.001, r=0.24), and hours reading mammogram per week (p=0.04, r= 0.19). The ROC method indicated that determinants of performance were confined to years reading mammograms (p=0.02, r = 0.2), and number of mammograms read per year (p=0.04, r=0.23). Conclusion: This work demonstrates the practical impact on study conclusions when different methodologies are used. The location sensitivity approach employed and statistical power with JAFROC, would suggest that the findings from this approach should be prioritized.

Does the thinking aloud condition affect the search for pulmonary nodules

Aim: To measure the effect of thinking aloud on perceptual accuracy and visual search behavior during chest radiograph interpretation for pulmonary nodules. Background: Thinking Aloud (TA) is an empirical research method used by researchers in cognitive psychology and behavioural analysis. In this pilot study we wanted to examine whether TA had an effect on the perceptual accuracy and search patterns of subjects looking for pulmonary nodules on adult posterioranterior chest radiographs (PA CxR). Method: Seven academics within Medical Radiation Sciences at The University of Sydney participated in two reading sessions with and without TA. Their task was to localize pulmonary nodules on 30 PA CxR using mouse clicks and rank their confidence levels of nodule presence. Eye-tracking recordings were collected during both viewing sessions. Time to first fixation, duration of first fixation, number of fixations, cumulative time of fixation and total viewing time were analysed. In addition, ROC analysis was conducted on collected outcome using DBM methodology. Results: Time to first nodule fixation was significantly longer (p=0.001) and duration of first fixation was significantly shorter (p=0.043). No significant difference was observed in ROC AUC scores between control and TA conditions. Conclusion: Our results confirm that TA has little effect on perceptual ability or performance, except for prolonging the task. However, there were significant differences in visual search behavior. Future researchers in radio-diagnosis could use the think aloud condition rather than silence so as to more closely replicate the clinical scenario.

A novel phantom system facilitating better descriptors of density within mammographic images

High mammographic density is a risk factor for breast cancer. As it is impossible to measure actual weight or volume of fibroglandular tissue evident within a mammogram, it is hard to know the correlation between measured mammographic density and the actual fibroglandular tissue volume. The aim of this study is to develop a phantom that represents glandular tissue within an adipose tissue structure so that correlations between image feature descriptors and the synthesised glandular structure can be accurately quantified. In this phantom study, ten different weights of fine steel wool were put into gelatine to simulate breast structure. Image feature descriptors are investigated for both the whole phantom image and the simulated density. Descriptors included actual area and percentage area of density, mean pixel intensity for the whole image and dense area, standard deviation of mean intensity, and integrated pixel density which is the production of area and mean intensity. The results show high level correlation between steel-wool weight and percentage density measured on images (r = 0.8421), and the integrated pixel density of dense area (r = 0.8760). The correlation is significant for mean intensity standard deviation for the whole phantom (r = 0.8043). This phantom study may help identify more accurate descriptors of mammographic density, thus facilitating better assessments of fibroglandular tissue appearances.