Diaphanography as a means of detecting breast cancer

Multispectral breast image grayscale and quality enhancement by repeated pair image registration & accumulation method

Nowadays, for detecting breast cancer in its early stages, the focus is on multispectral transmission imaging. Frame accumulation is a promising technique to enhance the grayscale level of the multispectral transmission images. Still, during the image acquisition process, human respiration or camera jitter causes the displacement of the frame's sequence which leads to the loss of accuracy and image quality of the frame accumulated image is reduced. In this article, we have proposed a new method named "repeated pair image registration and accumulation "to resolve the issue. In this method first pair of images from the sequence is first registered and accumulated followed by the next pair to be registered and accumulated. Then these two accumulated frames are registered and accumulated again. This process is repeated until all the frames from the sequence are processed and the final image is obtained. This method is tested on the sequence of breast frames taken at 600 nm, 620 nm, 670 nm, and 760 nm wavelength of light and proved the enhancement of quality, accuracy, and grayscale by various mathematical assessments. Furthermore, the processing time of our proposed method is very low because descent gradient optimization algorithm is used here for image registration purpose. This optimization algorithm has high speed as compared to other methods and is verified by registering a single image of each wavelength by three different methods. It has laid the foundations of early detection of breast cancer using multispectral transmission imaging.

Partial Verification Bias Correction Using Inverse Probability Bootstrap Sampling for Binary Diagnostic Tests

In medical care, it is important to evaluate any new diagnostic test in the form of diagnostic accuracy studies. These new tests are compared to gold standard tests, where the performance of binary diagnostic tests is usually measured by sensitivity (Sn) and specificity (Sp). However, these accuracy measures are often biased owing to selective verification of the patients, known as partial verification bias (PVB). Inverse probability bootstrap (IPB) sampling is a general method to correct sampling bias in model-based analysis and produces debiased data for analysis. However, its utility in PVB correction has not been investigated before. The objective of this study was to investigate IPB in the context of PVB correction under the missing-at-random assumption for binary diagnostic tests. IPB was adapted for PVB correction, and tested and compared with existing methods using simulated and clinical data sets. The results indicated that IPB is accurate for Sn and Sp estimation as it showed low bias. However, IPB was less precise than existing methods as indicated by the higher standard error (SE). Despite this issue, it is recommended to use IPB when subsequent analysis with full data analytic methods is expected. Further studies must be conducted to reduce the SE.

Approximate confidence intervals for the likelihood ratios of a binary diagnostic test in the presence of partial disease verification

The classic parameters used to assess the accuracy of a binary diagnostic test (BDT) are sensitivity and specificity. Other parameters used to describe the performance of a BDT are likelihood ratios (LRs). The LRs depend on the sensitivity and the specificity of the diagnostic test, and they reflect how much greater the probability of a positive or negative diagnostic test result for individuals with the disease than that for the individuals without the disease. In this study, several confidence intervals are studied for the LRs of a BDT in the presence of missing data. Two confidence intervals were studied through the method of maximum likelihood and seven confidence intervals were studied by applying the multiple imputation by chained equations method. A program in R software has been written that allows us to solve the estimation problem posed. The results obtained have been applied to the two real examples.

Diagnostic Accuracy of Lightscanning and Mammography in Women with Dense Breasts

The diagnostic accuracy of lightscanning and mammography in 610 breasts with mammographically dense parenchymal patterns was investigated. Lightscanning identified 31 out of 36 cancers and mammography 32. Lightscanning and mammography were in agreement in 28 cases of cancer. One non-invasive lobular carcinoma was not identified by either modality. Four cancers were not correctly identified with lightscanning alone and 3 cancers with mammography alone. Of the 574 breasts without cancer, lightscanning falsely denoted 101 (18%) as possibly being cancerous (false-positives). The corresponding figure for mammography was 25 (4%). Thus, lightscanning, as performed in this study, has the same sensitivity as mammography in detecting cancer in mammographically dense breasts. However, its usefulness is limited by a low predictive value of a positive test (high rate of false-positives).

Relation between Lightscanning and the Histologic and Mammographic Appearance of Malignant Breast Tumors

The relation between real-time transillumination (lightscanning) and the histologic appearance of 243 breast carcinomas was evaluated. Lightscanning mainly failed in identifying ductal and lobular carcinomas in situ. The result of lightscanning was also poor regarding small, invasive carcinomas. The absorption patterns in elastosis and scar tissue associated with carcinoma played no important role in the ability of lightscanning to identify a cancer. The relation between the lightscanning and mammographic appearance of 85 breast cancers from the same material was also evaluated. Lightscanning performed poorly in identifying tumors characterized by calcifications as compared to tumors with other mammographic appearances. However, the difference was not significant.

Spatial and Spectral Information in Optical Mammography

This article reviews our research activities in the area of optical mammography and relates them to the historical developments and the current state and trends in the field. The guiding threads for this article are the roles played in optical mammography by spatial and spectral information. The first feature, spatial information, is limited by the diffusive nature of light propagation but can take advantage of the exceptionally high optical contrast featured by blood vessels and blood-rich areas in the breast. We describe a method to correct for edge effects, a spatial second-derivative algorithm, and a two-dimensional phased-array approach that enhance the image contrast, the spatial resolution, and the depth discrimination in optical mammograms. The second feature, spectral information, is the most powerful and unique capability of optical mammography, and allows for functional measurements associated with hemoglobin concentration and oxygenation, water concentration, lipids content, and the wavelength dependence of tissue scattering. We present oxygenation-index images obtained from multi-wavelength optical data that point to the diagnostic potential of oxygenation information in optical mammography. The optimization of the spatial and spectral information in optical mammography has the potential to create a role for this imaging modality in the detection and monitoring of breast cancer.

Broadband optical mammography instrument for depth-resolved imaging and local dynamic measurements

We present a continuous-wave instrument for non-invasive diffuse optical imaging of the breast in a parallel-plate transmission geometry. The instrument measures continuous spectra in the wavelength range 650-1000 nm, with an intensity noise level <1.5% and a spatial sampling rate of 5 points/cm in the x- and y-directions. We collect the optical transmission at four locations, one collinear and three offset with respect to the illumination optical fiber, to recover the depth of optical inhomogeneities in the tissue. We imaged a tissue-like, breast shaped, silicone phantom (6 cm thick) with two embedded absorbing structures: a black circle (1.7 cm in diameter) and a black stripe (3 mm wide), designed to mimic a tumor and a blood vessel, respectively. The use of a spatially multiplexed detection scheme allows for the generation of on-axis and off-axis projection images simultaneously, as opposed to requiring multiple scans, thus decreasing scan-time and motion artifacts. This technique localizes detected inhomogeneities in 3D and accurately assigns their depth to within 1 mm in the ideal conditions of otherwise homogeneous tissue-like phantoms. We also measured induced hemodynamic changes in the breast of a healthy human subject at a selected location (no scanning). We applied a cyclic, arterial blood pressure perturbation by alternating inflation (to a pressure of 200 mmHg) and deflation of a pneumatic cuff around the subject's thigh at a frequency of 0.05 Hz, and measured oscillations with amplitudes up to 1 μM and 0.2 μM in the tissue concentrations of oxyhemoglobin and deoxyhemoglobin, respectively. These hemodynamic oscillations provide information about the vascular structure and functional integrity in tissue, and may be used to assess healthy or abnormal perfusion in a clinical setting.

Towards non-invasive characterization of breast cancer and cancer metabolism with diffuse optics

We review recent developments in diffuse optical imaging and monitoring of breast cancer, i.e. optical mammography. Optical mammography permits non-invasive, safe and frequent measurement of tissue hemodynamics oxygen metabolism and components (lipids, water, etc.), the development of new compound indices indicative of the risk and malignancy, and holds potential for frequent non-invasive longitudinal monitoring of therapy progression.

Multiple imputation for correcting verification bias

In the case in which all subjects are screened using a common test and only a subset of these subjects are tested using a golden standard test, it is well documented that there is a risk for bias, called verification bias. When the test has only two levels (e.g. positive and negative) and we are trying to estimate the sensitivity and specificity of the test, we are actually constructing a confidence interval for a binomial proportion. Since it is well documented that this estimation is not trivial even with complete data, we adopt multiple imputation framework for verification bias problem. We propose several imputation procedures for this problem and compare different methods of estimation. We show that our imputation methods are better than the existing methods with regard to nominal coverage and confidence interval length.

Characterization of benign and malignant breast lesions with computed tomography laser mammography (CTLM): initial experience

OBJECTIVES

The aim of this study was to characterize benign and malignant breast lesions with computed tomography-laser mammography (CTLM).

MATERIALS AND METHODS

In a prospective study, 100 female patients with 105 breast lesions classified as BIRADS IV to V at mammography underwent mammography, CTLM, and histologic verification at our institution. CTLM images were analyzed by radiologists with knowledge of the lesion's position but who were blinded to histology and morphologic findings from mammography. Two radiologists independently evaluated whether there was increased absorption, a sign of malignancy, on CTLM and assessed the appearance (volumes or linear branching) and shape (round or irregular) of the lesions.

RESULTS

Histologic analysis revealed 55 benign (52.4%) and 50 malignant (47.6%) breast lesions. Increased absorption was observed significantly more often in malignant than in benign lesions (70.0% vs. 32.7%, P = 0.028). Invasive cancer showed increased absorption in 76.2%, and ductal carcinoma in situ in 37.5%. Common morphologic characteristics of increased absorption were "volumes" (85.7% of malignant and 77.8% of benign lesions) with round shape (78.1% of malignant and 73.3% of benign lesions).

CONCLUSION

Our data indicate that CTLM, when used as an adjunct to mammography, may provide additional information to characterize benign and malignant breast lesions.

Verification and incorporation biases in studies assessing screening tests: prostate-specific antigen as an example

OBJECTIVES

Prostate-specific antigen (PSA) measurement is a widely used screening test for prostate cancer. However, studies assessing the performance of PSA suffer from verification bias and incorporation bias, because men with PSA levels less than 4 ng/mL do not undergo biopsy unless the digital rectal examination findings are suspicious for prostate cancer. We have reviewed how these biases have influenced such studies.

METHODS

We compared the results of three studies that reported on the test characteristics of PSA, taking into account the types of bias present. We applied approximate verification bias corrections to previously reported age-specific reference ranges, based on the reported 22% cancer detection rate in the PSA range 2.5 to 4 ng/mL. To adjust for incorporation bias, we removed PSA from the criteria establishing the absence of prostate cancer and recalculated the test characteristics of PSA.

RESULTS

Verification bias led to an elevation in the sensitivity estimates of PSA. The specificity increased or decreased depending on the type of bias present. After accounting for incorporation bias, the sensitivity of PSA testing at a 4-ng/mL cutoff level was less than 67%, and the specificity was more than 80.6%.

CONCLUSIONS

Studies evaluating PSA testing have been biased because of the presence of verification and incorporation biases. Future studies must consider the possibility of these biases to obtain valid results.

Correcting for verification bias in studies of a diagnostic test's accuracy

Standard methods for assessing the accuracy of diagnostic tests require determination of true disease status for each study patient. In practice, some study patients might not have verified disease status. If the decision to verify a patient is influenced by the test result, analysis using only verified cases might lead to biased results, commonly known as verification bias. This paper reviews recent developments in bias-correction methods for studies on the accuracy of diagnostic tests.

Diagnostic imaging with light

This paper reviews the evolution of optical imaging in diagnostic radiology and examines recent progress. Although the idea has been around for many decades, interest in the development of an effective method has never been so great. Optical imaging presents several potential advantages over existing radiological techniques. First, the radiation is non-ionizing and therefore reasonable doses can be repeatedly employed without harm to the patient. Second, optical methods offer the potential to differentiate between soft tissues with different optical absorption or scatter, but which are indistinguishable using other modalities. And third, specific absorption by natural chromophores (such as haemoglobin) allows functional information to be obtained. Principal clinical applications include a means of detecting breast disease and a cerebral imaging modality for mapping oxygenation and haemodynamics in the brain of newborn infants or cortical functional activity in adults. Past attempts to image tissues with light have been severely restricted by the overwhelming scatter which occurs when optical radiation spreads through tissue: however, recent innovations in technology have suggested once again that it may be a practical possibility.

Optical time-of-flight and absorbance imaging of biologic media

Imaging the interior of living bodies with light may assist in the diagnosis and treatment of a number of clinical problems, which include the early detection of tumors and hypoxic cerebral injury. An existing picosecond time-of-flight and absorbance (TOFA) optical system has been used to image a model biologic system and a rat. Model measurements confirmed TOFA principles in systems with a high degree of photon scattering; rat images, which were constructed from the variable time delays experienced by a fixed fraction of early-arriving transmitted photons, revealed identifiable internal structure. A combination of light-based quantitative measurement and TOFA localization may have applications in continuous, noninvasive monitoring for structural imaging and spatial chemometric analysis in humans.

Lightscanning versus mammography for the detection of breast cancer in screening and clinical practice. A Swedish multicenter study

State of the art lightscanning of the breast was tested against mammography in 2568 women in a Swedish multicenter study. The study was in two parts. One was in women with symptoms from the breasts (the clinical study) comprising 3178 examined breasts with 198 cancers; the other in asymptomatic women (the screening study) comprising 1909 examined breasts with 126 cancers. In women with symptoms from the breasts, lightscanning did not contribute to clinical examination and mammography. In the screening situation, it was poor to pick up small cancers. Mammography alone falsely diagnosed cancer in 6.9% of the patients whereas lightscan falsely diagnosed cancer in 19.1%. Lightscan was not better than mammography in young women. The study shows that lightscanning in its current form is inferior to standard mammography.

Imaging of the breast: techniques and results

Procedures for imaging of the breast have increased in number substantially in the past 30 years. Mammography, currently the most important breast imaging technique, was introduced at the Mayo Clinic in 1961. In 1988, more than 36,000 mammographic procedures were done. Breast ultrasonography is also a valuable examination, particularly for determining whether mass lesions are cystic or solid. The use of mammography for screening is increasing. Screening mammography allows the detection of breast cancer before it is palpable and while it is still in a stage known as minimal breast cancer. Lesions metastatic to axillary lymph nodes are less common in women with nonpalpable breast cancers than in women with palpable lesions. Nondiagnostic mammography should not delay the biopsy of a mass that is suspicious on physical examination. A special breast imaging center for performance of screening studies and evaluation of breast problems has been established at the Mayo Clinic.

Chrono-coherent imaging for medicine

We describe a new method for imaging with visible and near visible light inside media, such as tissues, which have strong light scattering. The chrono-coherent imaging (CCI) method is demonstrated in this paper for a transmission geometry where an absorbing object is completely hidden from normal visual observation by light scattering of the media. The resultant images are most similar to X rays, with cumulative transmission showing absorption features and refractive index differences in the media. We discuss laser coherence properties, coherence measurements, the relation of CCI to light-inflight holography, holographic film properties relevant to CCI, a particular optical setup for CCI, the results of a demonstration experiment imaging an absorbing object hidden by light scattering, and an experiment to estimate the clinical applicability of CCI.

Chrono-coherent imaging for medicine

Imaging inside the body with optical wavelengths encounters problems due to light scattering of tissues and other optical distortions. A description is given of chrono-coherent imaging (CCI), a new method for imaging with visible and near-infrared light that uses coherent image formation and subpicosecond timing to remove the time-delayed scattered light. With CCI it is possible to form images in the presence of the overwhelming amount of scattered light that blocks conventional image formation. The coherent image formation process allows the use of long-duration, high-total-energy, and modest-peak-power pulses to overcome scattering losses. CCI is an extension of light-in-flight holography, which combines the properties of short-duration pulses and hologaphy for various measurements of objects and optical wavefronts.

An evaluation of transmission spectroscopy (lightscanning) in the diagnosis of symptomatic breast lesions

A prospective study of transmission spectroscopy (lightscanning) has been performed on 285 women presenting with symptomatic breast disease to one outpatient clinic. Of the 41 patients with histologically confirmed breast cancer lightscanning detected 36 (87.8%). In the study group 164 patients had both lightscans and mammography performed and, of the 30 biopsy-proven carcinomas in this group, lightscanning detected 26 (87%) and mammography 25 (83%). Lightscanning was positive in five of the six non-invasive breast cancers and in 13 of the 15 invasive carcinomas 2 cm or less in diameter. No carcinoma was misdiagnosed as benign when the results of both investigations were combined.

Biases in the assessment of diagnostic tests

Diagnostic tests are traditionally characterized by simple measures of efficacy such as the sensitivity and the specificity. These measures, though widely recognized and easy to understand, are subject to definitional arbitrariness. Moreover, studies constructed to estimate the sensitivity and specificity are susceptible to a variety of biases. In this paper the various potential problems are described with reference to examples from the diagnostic literature. These difficulties have implications for the design of diagnostic test evaluations, and the choice of suitable measures of test efficacy.

The development of a system for transillumination computed tomography

A transillumination computed tomography system has been developed for studies of the breast, testes, neonatal skull and peripheral limbs. Initial experiments on test objects have emphasised the problems of scattering and geometrical dependence of lesion detection that are likely to be encountered in conventional diaphanography, but have demonstrated the feasibility of computed tomography as a means of improving the sensitivity of the transillumination technique. The problems of transillumination computed tomography have been addressed and further areas of research identified.

Imaging of the breast

A multitude of techniques for imaging and evaluating the breast have been described. Based upon current evidence, thermography does not appear to have any established clinical indications. Computed tomography, ultrasonography, lightscanning, and NMR may be useful as adjuncts to mammography, and further research seems warranted. Mammography remains the "gold standard" in breast imaging, however. Its ability to detect clinically occult disease makes it the superior imaging technique in the breast, and the only technique indicated for screening. In light of the information presented in this article, it is hoped that the trend away from mammography in favor of so-called "noninvasive" breast imaging techniques will be reversed until such time that the efficacy of these other modalities has been proven. A proper process for the evaluation and clinical testing of the newer breast imaging modalities has been defined. Using this as a guideline, it is hoped that the indiscriminate clinical use of unproven techniques will be avoided.