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 effectiveness of screening mammography in detecting breast cancer relies heavily on accurate observer performance;¹ however, miss rates of 10–30% have been reported.^2,3 The challenge for radiologists is to gain comprehensive experience in the appearance of abnormality and keep their recall rate within acceptable limits given the low incidence of the disease.^4–6 It has been proposed that the insertion of “test malignant cases” into a “real life” clinical screening mammography set may increase cancer detection rates by artificially increasing the prevalence.⁷ However, by specifically increasing the prevalence of abnormality, there may be inadvertent effects on the detection of subsequent “real” cases.Previous work on the impact on increasing abnormality prevalence on radiologic performance has provided diverse conclusions, with one study suggesting that varying prevalence was unlikely to alter the accuracy of the radiologists,⁸ another suggesting increased diagnostic efficacy with increasing prevalence⁹ and a further arguing no significant effect.¹⁰ A study focusing on prevalence expectation, whilst showing no significant impact on reporting accuracy, did show that visual search, in terms of interpretation time and the number of visual fixations per image, was significantly changed when higher prevalence was expected.¹¹A recent study of expert breast radiologists showed that they tend to miss a much higher percentage of malignant lesions in a setting closer to the actual low-prevalence level found in the clinic than under high prevalence test conditions.⁷ However, in that study, although the false-negative rate significantly increased in the clinic setting, the false-positive rate decreased in the low-prevalence condition, although by a non-significant amount. Moreover, owing to the difficulties of performing such a study in the clinical setting, the same radiologists did not interpret the same inserted cases in both the low and high prevalence parts of the study, and as reader variability usually comprises the largest component of variance in a reader study, care should be taken when interpreting these results.Research in cognitive psychology has shown that human visual perception of the elements in our environment is greatly dependent on what was previously seen.¹² For example, detection of a target is facilitated by having seen the target (or a lookalike) before, and this effect is called “perceptual priming”. Perceptual priming as a mechanism for improving cancer detection in low-prevalence contexts such as screening mammography is an under explored area of research. In this context, priming can be understood as a mechanism that “highlights” the presence of a given target by increasing the saliency of the stimulus.¹³ It is generally accepted in the cognitive psychology literature that priming can be used to direct visual attention towards an explicit target, and that observers become proficient at finding targets when salient prompts are employed.^14,15 This has real relevance in clinical imaging, not just as an attempt to improve diagnostic efficacy but also to establish the impact of audit cases randomly inserted into a reading set to test radiologic performance. The hypothesis of the study is that the addition of malignant cases of lower difficulty (herein called “primers”) would increase the likelihood that the readers would detect subsequent malignant cases of higher difficulty presented at intervals between one and five cases after the primers.     

Relationship between changes in pulmonary kinetics and autonomic regulation of blood flow

Various regulatory mechanisms of pulmonary oxygen uptake () kinetics have been postulated. The purpose of this study was to investigate the relationship between vagal withdrawal, measured using RMSSDRR, the root mean square of successive differences in cardiac interval (RR) kinetics, a mediator of oxygen delivery, and kinetics. Forty‐nine healthy adults (23 ± 3 years; 72 ± 13 kg; 1.80 ± 0.08 m) performed multiple repeat transitions to moderate‐ and heavy‐intensity exercise. Electrocardiography, impedance cardiography, and pulmonary gas exchange parameters were measured throughout; time domain measures of heart rate variability were subsequently derived. The parameters describing the dynamic response of , cardiac output () and RMSSDRR were determined using a mono‐exponential model. During heavy‐intensity exercise, the phase II τ of was significantly correlated with the τ of RR (r = 0.36, P < 0.05), Q (r = 0.67, P < 0.05), and RMSSDRR (r = 0.38, P < 0.05). The τ describing the rise in Q explained 47% of the variation in τ, with 30% of the rate of this rise in Q explained by the τ of RR and RMSSDRR. No relationship was evident between kinetics and those of Q, RR, or RMSSDRR during moderate exercise. Vagal withdrawal kinetics support the concept of a centrally mediated oxygen delivery limitation partly regulating kinetics during heavy‐, but not moderate‐, intensity exercise.     

Technical considerations in the use of polymethylmethacrylate in cranioplasty

Polymethylmethacrylate (PMMA) is a self-curing acrylic resin that can be used in the repair of cranial defects. It is available in three forms: PMMA without mesh, PMMA reinforced with mesh, and PMMA preformed to fit a defect. In cranioplasty, the size and location of the defects provide the selection criteria for the use of PMMA. PMMA without mesh is ideal for small defects (5 cm2-15 cm2). PMMA reinforced with mesh is used for moderate sized defects (16 cm2-49 cm2). For very large defects (> or = 50 cm2), a CT scan guided mold is recommended because it provides the ideal contour and shape that simulates the normal skull.     

Segmental renal infarction after blunt abdominal trauma: Clinical significance and appropriate management

Segmental infarction after blunt trauma is an uncommon type of injury occurring as a result of occlusion of a segmental renal artery. We retrospectively reviewed 32 cases of segmental renal infarction after nonpenetrating injury in order to assess the clinical significance and the most appropriate management. Thirty-five segmental infarcts were demonstrated by contrast medium-enhanced computed tomography (CT), 19 in the left and 16 in the right kidney. Twenty-five of the 35 infarcts (71%) occurred as an isolated renal injury. A distinct upper pole predilection for segmental infarct was observed. Angiography showed an occluded branch vessel without contrast medium extravasation in four cases. None of the 30 surviving patients experienced delayed renal hemorrhage or deterioration of renal function. Only 2 of 24 evaluable patients developed mild diastolic hypertension during follow-up. Our data indicate that segmental renal infarction in the blunt trauma patient, as demonstrated by contrast medium-enhanced CT, should be managed nonoperatively and requires no further evaluation with angiography.     

Comparison of three intra-oral storage phosphor systems using subjective image quality

OBJECTIVE: To compare the subjective image quality of three intra-oral storage phosphor systems. METHODS: DenOptix (Dentsply/Gendex, Chicago, IL, USA), Digora (Soredex, Helsinki, Finland), and CD-Dent (DigiDent Digital Imaging Technologies, Nesher, Israel) were compared. Two different imaging plates (IPs), BAS300 and HR300 (Fuji Photo Film Co., Tokyo, Japan) were used with the DenOptix system. The specimen was the maxilla and surrounding soft tissues of an adult cadaver. Imaging was at 70 kVp and 8 mA with a focus-detector distance of 38 cm using an optical bench. The exposure times were varied and a panel of five dentists independently evaluated the images produced with each system/IP receptor for seven features; proximal caries, gingival soft tissues, cortical bone, root canal space, root apices, periodontal ligament space and endodontic instrument clarity on a three-interval confidence scale. The best three exposures were chosen according to the highest scores for each system. These images were re-read in random order a total of 10 times. Pair-wise comparisons were made by use of odd's ratio analysis. A 95% confidence interval was applied. RESULTS: Images made with the DenOptix system/BAS IP combination were perceived to have the best overall image quality. The DenOptix/HR IP combination and Digora were rated almost equally in second place. The DigiDent system was ranked inferior. The Digora was considered to be the best for demonstrating gingival soft tissues (P < 0.05) and the DenOptix/HR300 combination the best for clarity of endodontic instruments (P < 0.05). CONCLUSIONS: While the DenOptix/BAS 300 combination was rated highest overall, the ranking of image quality by modality was found to be task-dependent. Digora was rated best for demonstrating gingival soft tissues.     

A genome-wide view of Caenorhabditis elegans base-substitution mutation processes

Knowledge of mutation processes is central to understanding virtually all evolutionary phenomena and the underlying nature of genetic disorders and cancers. However, the limitations of standard molecular mutation detection methods have historically precluded a genome-wide understanding of mutation rates and spectra in the nuclear genomes of multicellular organisms. We applied two high-throughput DNA sequencing technologies to identify and characterize hundreds of spontaneously arising base-substitution mutations in 10 Caenorhabditis elegans mutation-accumulation (MA)-line nuclear genomes. C. elegans mutation rate estimates were similar to previous calculations based on smaller numbers of mutations. Mutations were distributed uniformly within and among chromosomes and were not associated with recombination rate variation in the MA lines, suggesting that intragenomic variation in genetic hitchhiking and/or background selection are primarily responsible for the chromosomal distribution patterns of polymorphic nucleotides in C. elegans natural populations. A strong mutational bias from G/C to A/T nucleotides was detected in the MA lines, implicating oxidative DNA damage as a major endogenous mutagenic force in C. elegans. The observed mutational bias also suggests that the C. elegans nuclear genome cannot be at equilibrium because of mutation alone. Transversions dominate the spectrum of spontaneous mutations observed here, whereas transitions dominate patterns of allegedly neutral polymorphism in natural populations of C. elegans and many other animal species; this observation challenges the assumption that natural patterns of molecular variation in noncoding regions of the nuclear genome accurately reflect underlying mutation processes.     

Cloning and characterization of voltage‐gated calcium channel alpha1 subunits in Xenopus laevis during development

Voltage‐gated calcium channels play a critical role in regulating the Ca²⁺ activity that mediates many aspects of neural development, including neural induction, neurotransmitter phenotype specification, and neurite outgrowth. Using Xenopus laevis embryos, we describe the spatial and temporal expression patterns during development of the 10 pore‐forming alpha1 subunits that define the channels' kinetic properties. In situ hybridization indicates that Ca_V1.2, Ca_V2.1, Ca_V2.2, and Ca_V3.2 are expressed during neurula stages throughout the neural tube. These, along with Ca_V1.3 and Ca_V2.3, beginning at early tail bud stages, and Ca_V3.1 at late tail bud stages, are detected in complex patterns within the brain and spinal cord through swimming tadpole stages. Additional expression of various alpha1 subunits was observed in the cranial ganglia, retina, olfactory epithelium, pineal gland, and heart. The unique expression patterns for the different alpha1 subunits suggests they are under precise spatial and temporal regulation and are serving specific functions during embryonic development. Developmental Dynamics 238:2891–2902, 2009. © 2009 Wiley‐Liss, Inc.