20 research outputs found
The impact of simulated motion blur on breast cancer detection performance in full field digital mammography (FFDM)
Objective: Full-field Digital Mammography (FFDM) is employed in breast screening for the early detection of breast cancer. High quality, artefact free, diagnostic images are crucial to the accuracy of this process. Unwanted motion during the image acquisition phase and subsequent image blurring is an unfortunate occurrence in some FFDM images. The research detailed in this thesis seeks to understand the impact of motion blur on cancer detection performance in FFDM images using novel software to perform simulation of motion, an observer study to measure the lesion detection performance and physical measures to assess the impact of simulated motion blur on image characteristics of the lesions. Method: Seven observers (15±5 years’ reporting experience) evaluated 248 cases (62 containing malignant masses, 62 containing malignant microcalcifications and 124 normal cases) for three conditions: no motion blur (0.0 mm) and two magnitudes of simulated motion blur (0.7 mm and 1.5 mm). Abnormal cases were biopsy proven. A free-response observer study was conducted to compare lesion detection performance for the three conditions. Equally weighted jackknife alternative free-response receiver operating characteristic (wJAFROC) was used as the figure of merit. A secondary analysis of data was deemed important to simulate ‘double reporting’. In this secondary analysis, six of the observers are combined with the seventh observer to evaluate the impact of combined free-response data for lesion detection and to assess if combined two observers data could reduce the impact of simulated motion blur on detection performance. To compliment this, the physical characteristics of the lesions were obtained under the three conditions in order to assess any change in characteristics of the lesions when blur is present in the image. The impact of simulated motion blur on physical characteristics of malignant masses was assessed using a conspicuity index; for microcalcifications, a new novel metric, known as dispersion index, was used. Results: wJAFROC analysis found a statistically significant difference in lesion detection performance for both masses (F (2,22) = 6.01, P=0.0084) and microcalcifications (F(2,49) = 23.14, P<0.0001). For both lesion types, the figure of merit reduced as the magnitude of simulated motion blur increased. Statistical differences were found between some of the pairs investigated for the detection of masses (0.0mm v 0.7mm, and 0.0mm v 1.5mm) and all pairs for microcalcifications (0.0 mm v 0.7 mm, 0.0 mm v 1.5 mm, and 0.7 mm v 1.5 mm). No difference was detected between 0.7 mm and 1.5 mm for masses. For combined two observers’ data of masses, there was no statistically significant difference between single and combined free-response data for masses (F(1,6) = 4.04, p=0.1001, -0.031 (-0.070, 0.008) [treatment difference (95% CI)]. For combined data of microcalcifications, there was a statistically significant difference between single and combined free-response data (F(1,6) = 12.28, p=0.0122, -0.056 (-0.095, -0.017) [treatment difference (95% CI)]. Regarding the physical measures of masses, conspicuity index increases as the magnitude of simulated motion blur increases. Statistically significant differences were demonstrated for 0.0–0.7 mm t(22)=-6.158 (p<0.000); 0.0–1.5 mm t(22)=-6.273 (p<0.000); and 0.7–1.5 mm (t(22)=-6.231 (p<0.000). Lesion edge angle decreases as the magnitude of simulated motion blur increases. Statistically significant differences were demonstrated for 0.0–0.7 mm t(22)=3.232 (p<0.004); for 0.0–1.5 mm t(22)=6.592 (p<0.000); and 0.7–1.5mm t(22)=2.234 (p<0.036). For the grey level change there was no statistically significant difference as simulated motion blur increases to 0.7 and then to 1.5mm. For image noise there was a statistically significant difference, where noise reduced as simulated motion blur increased: 0.0–0.7 mm t(22)=22.95 (p<0.000); 0.0–1.5mm t(22)=24.66 (p<0.000); 0.7–1.5 mm t(22)=18.11 (p<0.000). For microcalcifications, simulated motion blur had a negative impact on the ‘dispersion index’. Conclusion: Mathematical simulations of motion blur resulted in a statistically significant reduction in lesion detection performance. This reduction in performance could have implications for clinical practice. Simulated motion blur has a negative impact on the edge angle of breast masses and a negative impact on the image characteristics of microcalcifications. These changes in the image lesion characteristics appear to have a negative effect on the visual identification of breast cancer
Methodology for taking a computer-aided breast cancer screening system from the laboratory to the marketplace
Breast cancer is one of the most common causes of death in women, and yet is one
of the more 'curable' cancers if caught early. Since its inception in 1987, the Breast
Screening Programme has been the principal tool in the National Health Service's fight
to reduce the number of cancer related deaths in the UK.
Breast screening using mammography is widely viewed as the most effective way of
detecting early breast cancer, with the UK population of women over the age of 50
being invited to a screening session every three years. However, national shortages
of clinical staff willing to enter and remain in this field mean that the NHS Breast
Screening Programme is severely understaffed.
This thesis discusses one way in which technology can assist in the screening programme;
specifically, the use of a computer-aided cancer detection system. Here, we will present
the design and analysis of a sequence of experiments used to develop and evaluate such
a system. PROMAM (PROmpting for MAMmography) involved the scanning and
digitising of mammograms, and the subsequent analysis of the digital image by a series
of algorithms.
Initial evaluation was done to ensure that the algorithms were performing satisfactorily
at a technical level before being introduced into a clinical setting. Two large experiments
with the algorithms were designed and evaluated:
1. offering radiologists three levels of algorithm prompting and, as a control, an
unprompted level, on samples of mammographic films, with outcomes being their
recall rate and subjective views at each prompting level,
2. a pre-clinical experiment, conducted under semi-clinical conditions, where two
readers would see a batch of films seeded with higher than normal numbers of
cancers, with readers allocated randomly to prompted and unprompted views of
films.
The first experiment was designed using a Graeco-Latin Square, with three 'nuisance'
variables and the treatment factor of prompting levels (no prompts, low level of prompt¬
ing, medium and high). Four radiologists read at each level of prompting once, on dif¬
ferent sets of films. One of the more interesting results was that the recall rate did not
increase as the prompting rate rose - contrary to prior expectations. Most of the differ¬
ences seen between the prompting rates could be explained as radiologist differences.
Once these were taken into account, the level of prompting had little effect. Addition¬
ally, although the time taken to read a set of films increased as the prompting rate
increased (as would be expected), it was only an increase of 26% from the unprompted
set to the set with the highest number of prompts. Observational data suggested that
the lowest level of prompting was not maintaining the interest of the radiologist, thus
leading them to neglect the prompts.
The following experiment moved the system a step closer to a true clinical demonstra¬
tion of the efficacy of PROMAM, being conducted under semi-clinical conditions. Using
a method of minimisation, the number of cancers each radiologist viewed as first reader,
second reader, prompted or unprompted were balanced. Preliminary exploratory anal¬
ysis indicated that the recall rate declined with the introduction of the prompting
system, but more detailed, analysis indicated that much of this difference was due to
a
radiologist effect. Although cancer detection was slightly lower with the prompting
system, examination of the 11 cancers missed by the prompted radiologist showed that
six of these had been correctly prompted by the algorithms. This demonstrated scope
to improve the cancer detection rate by nearly 5%.
These experiments determined the 'production' version of the prompting system. A
design to evaluate the system in a sample of 100,000 women in six centres was produced,
but due to circumstances beyond the project team's control, it was not possible to take
this work to the stage of a full 'trial' of the system. The design concept can, however,
apply to the evaluation of any similar prompting system. The recommended design is
therefore presented, together with an analysis of data from a simulated application of
this design.
This simulation has allowed recommendations to be made on the most appropriate ways
to analyse the extensive and complicated dataset that will be obtained. In particular,
it identified technical problems that can arise from the application on one candidate
analytical method, and an explanation for the failure obtained
It is quite clear from the evidence presented in this thesis that there is much scope
for improvement in the cancer detection rate by the use of a prompting system, with¬
out a corresponding loss in the specificity. With the shortage of radiologists and ra¬
diographers, and the increasing demand placed on the Breast Screening Programme,
technology could play a beneficial role in screening for breast cancer in the coming
year
Effect of nutritional factors on the growth and production of biosurfactant by Pseudomonas aeruginosa strain 181
The growth and production of biosurfactant by P. seudomonas aeruginosa (181) was dependant on nutritional factors. Among the eleven carbon sources tested, glucose supported the maximum growth (0.25 g/L) with the highest biosurfactant yield and this was followed by glycerol. Glucose reduced the surface tension to 35.3 dyne/
cm and gave an E24 reading of 62.7%. Butanol gave the lowest growth and had no biosurfactant production.
For the nitrogen sources tested, casamino acid supported a growth of 0.21 g/L which reduced the surface tension to 41.1 dyne/cm and gave an E24 reading of 56%. Soytone was assimilated similarly, with good growth and high biosurfactant production. Corn steep liquor gave the lowest growth and did not show any biosurfactant activity
Aspects of the normal human breast
Studies have been made on normal tissue from 50 whole breasts
and 43 breast biopsies using subgross histological and duct
injection techniques. The results obtained from the various
investigations have been compared with factors which may affect the
breast, notably age, the menstrual cycle, parity and laterality.
It has been found that the ducts in the breast do not branch in
a simple dichotomous manner, nor are individual lactiferous systems
arranged about the nipple in discrete lobes like the spokes of a
wheel. Rather, the duct systems are interwoven with each other in
an intricate manner and may not be dissected out individually.
The quantity of parenchymatous lobules in the breast was found
to decrease significantly with age. Lobules occurred in areas of
high focal density and their number was not related to the amount
of fibrous stroma present. Lobules did not occur with greater
frequency in the upper outer quadrant of the breast and lobule
number was not related to tumour incidence. Parity and laterality
were without significance in the present study.
The presence of acid mucopolysaccharides in the intra-lobular
breast stroma showed a cyclical variation which peaked at approx¬
imately day 24 of the menstrual cycle. It is suggested that
hyaluronic acid is the principal component of the staining reaction
and may be associated with premenstrual water retention in the
breast. The incidence of intraluminal secretions within the
ductules of lobules, and intracellular granules within ductular cells, did not reveal cyclical variation.
Normal lobule types occurring in whole breasts were assessed by
subgross techniques and significant variations were recorded with
age. Parity and laterality were not of significance in these
results. Examination of breasts following injection of lactiferous
ducts with a radio-opaque medium indicated that more than one
subgross lobule type was associated with a single lactiferous duct
system.
Comparisons have been made between the radiographic and
subgross morphology of slices of breast tissue and results suggest
that the parenchymal content of the breast cannot be predicted from
radiographic appearances alone