Magnetic resonance imaging texture analysis classification of primary breast cancer.

OBJECTIVES: Patient-tailored treatments for breast cancer are based on histological and immunohistochemical (IHC) subtypes. Magnetic Resonance Imaging (MRI) texture analysis (TA) may be useful in non-invasive lesion subtype classification. METHODS: Women with newly diagnosed primary breast cancer underwent pre-treatment dynamic contrast-enhanced breast MRI. TA was performed using co-occurrence matrix (COM) features, by creating a model on retrospective training data, then prospectively applying to a test set. Analyses were blinded to breast pathology. Subtype classifications were performed using a cross-validated k-nearest-neighbour (k = 3) technique, with accuracy relative to pathology assessed and receiver operator curve (AUROC) calculated. Mann-Whitney U and Kruskal-Wallis tests were used to assess raw entropy feature values. RESULTS: Histological subtype classifications were similar across training (n = 148 cancers) and test sets (n = 73 lesions) using all COM features (training: 75%, AUROC = 0.816; test: 72.5%, AUROC = 0.823). Entropy features were significantly different between lobular and ductal cancers (p < 0.001; Mann-Whitney U). IHC classifications using COM features were also similar for training and test data (training: 57.2%, AUROC = 0.754; test: 57.0%, AUROC = 0.750). Hormone receptor positive and negative cancers demonstrated significantly different entropy features. Entropy features alone were unable to create a robust classification model. CONCLUSION: Textural differences on contrast-enhanced MR images may reflect underlying lesion subtypes, which merits testing against treatment response. KEY POINTS: • MR-derived entropy features, representing heterogeneity, provide important information on tissue composition. • Entropy features can differentiate between histological and immunohistochemical subtypes of breast cancer. • Differing entropy features between breast cancer subtypes implies differences in lesion heterogeneity. • Texture analysis of breast cancer potentially provides added information for decision making.

Quantitative analysis of cardiac left ventricular variables obtained by MRI at 3 T: a pre- and post-contrast comparison.

Short-axis cine images are acquired during cardiac MRI in order to determine variables of cardiac left ventricular (LV) function such as ejection fraction (EF), end-diastolic volume (EDV), end-systolic volume (ESV), stroke volume (SV) and LV mass. In cardiac perfusion assessments this imaging can be performed in the temporal window between first pass perfusion and the acquisition of delayed enhancement images in order to minimise overall scanning time. The objective of this study was to compare pre- and post-contrast short-axis LV variables of 15 healthy volunteers using a two-dimensional cardiac-gated segmented cine true fast imaging with steady state precession sequence and a 3.0 T MRI unit in order to determine the possible effects of contrast agent on the calculated cardiac function variables. Image analysis was carried out using semi-automated software. The calculated mean LV mass was lower when derived from the post-contrast images, relative to those derived pre-contrast (102 vs 108.1 g, p<0.0001). Small but systematic significant differences were also found between the mean pre- and post-contrast values of EF (69.4% vs 68.7%, p<0.05), EDV (142.4 vs 143.7 ml, p<0.05) and ESV (44.2 vs 45.5 ml, p<0.005), but no significant differences in SV were identified. This study has highlighted that contrast agent delivery can influence the numerical outcome of cardiac variables calculated from MRI and this was particularly noticeable for LV mass. This may have important implications for the correct interpretation of patient data in clinical studies where post-contrast images are used to calculate LV variables, since LV normal ranges have been traditionally derived from pre-contrast data sets.

Multicentre magnetic resonance texture analysis trial using reticulated foam test objects.

Texture analysis in magnetic resonance imaging has the ability to provide useful diagnostic information with respect to the discrimination of disease states of a single tissue or the separation of different tissues. However, for widespread use it is necessary to determine how texture measurements carried out in one center relate to those carried out in another. To this end, a multicentre trial has been performed where reticulated foam test objects have been scanned in six European centers according to a fixed protocol. It has been concluded that texture measurements are not transportable between centers. Principal component models calculated from the texture parameters collected in one center do not fit the data collected in another. Further trials are to investigate whether the reticulated foam test objects may be used to normalize tissue texture data collected in different centers.

The use of reticulated foam in texture test objects for magnetic resonance imaging.

The use of texture analysis in magnetic resonance imaging requires the availability of texture test objects for use in standardisation of in vivo measurement. A series of such objects of varying texture has been developed using reticulated foam, which has an open pore structure. The texture properties of these foams have been compared with in vivo brain and the ability of texture analysis to discriminate the different porosities of foam and brain (white matter) demonstrated.

Palliation of pain associated with metastatic bone cancer using samarium-153 lexidronam: a double-blind placebo-controlled clinical trial.

PURPOSE: To evaluate the effectiveness and safety of samarium-153 (153Sm) lexidronam (EDTMP) in a double-blind, placebo-controlled study. PATIENTS AND METHODS: Patients with painful bone metastases secondary to a variety of primary malignancies were randomized to receive 153Sm-EDTMP 0.5 or 1.0 mCi/kg, or placebo. Treatment was unblinded for patients who did not respond by week 4, with those who had received placebo eligible to receive 1.0 mCi/kg of active drug in an open-label manner. Patient and physician evaluations were used to assess pain relief, as was concurrent change in opioid analgesia. RESULTS: One hundred eighteen patients were enrolled onto the study. Patients who received 1.0 mCi/kg of active drug had significant reductions in pain during each of the first 4 weeks in both patient-rated and physician-rated evaluations. Pain relief was observed in 62% to 72% of those who received the 1.O-mCi/kg dose during the first 4 weeks, with marked or complete relief noted in 31% by week 4. Persistence of pain relief was seen through week 16 in 43% of patients who received 1.0 mCi/kg, of active drug. A significant correlation (P = .01) was observed between reductions in opioid analgesic use and pain scores only for those patients who received 1.0 mCi/kg 153Sm-EDTMP. Bone marrow suppression was mild, reversible, and not associated with grade 4 toxicity. CONCLUSION: A single dose of 1.0 mCi/kg of 153Sm-EDTMP provided relief from pain associated with bone metastases. Pain relief was observed within 1 week of administration and persisted until at least week 16 in the majority of patients who responded.

Performance assessment and quality control in MRI by Eurospin test objects and protocols.

As part of its work, the European Concerted Action "Tissue Characterisation by MRS and MRI" (COMAC-BME) has expended considerable effort in the field of magnetic resonance imaging (MRI) quality control. A set of test objects--the Eurospin set--have been designed and rigorously tested in many systems throughout Europe. The full history of this development is described, together with a detailed presentation of the types of measurements that are achievable with such test objects and examples of the results. Further, the principles of more complex Stage II tests (which involve invasive interaction with the system) are introduced. Finally, simplified methods of quantifying the overall performance are discussed and the levels of MRI quality control from acceptance testing to routine quality assurance outlined.

Trial of modifications to Eurospin MRI test objects.

The original design of the Eurospin test objects (Magn. Reson. Imaging 6:195-199; 1988) for the assessment of magnetic resonance imaging (MRI) image quality, was subjected to re-evaluation at several meetings during the subsequent years, culminating in some changes to the designs. Further, an annulus filled with saline was added to the set with the purpose of simulating the loading of the receiver coils normal in clinical use. All of these modified test objects were circulated among 8 European centres in a detailed experimental trial of their utility. The results are presented, indicating increased success and enhanced functionality of this set of test objects.

MR image texture analysis--an approach to tissue characterization.

The role and value of texture analysis in the quantification of medical images is reviewed and the various methods described. The promise in magnetic resonance imaging is discussed and the coordinated research programme being carried out within the framework of the European Economic Community Concerted Action on Tissue Characterization by MRS and MRI is outlined. Tissue characterization of the human brain has been performed by texture analysis of proton relaxation time images using a standard MR whole body imager operating at 1.5 T and the results are presented.

A test material for tissue characterisation and system calibration in MRI.

A tissue-equivalent test material for MRI has been produced from a polysaccharide gel, agarose, containing gadolinium chloride chelated to EDTA. By varying the amounts of each constituent, the T1 and T2 of the material can be varied independently. As a result, the entire range of in vivo tissue relaxation times can be covered. Through the mathematical modelling of the 1H relaxation theories for both the gel and chelated paramagnetic ion, it has been possible to create a material with relaxation properties and behaviour predictable as functions of both the Larmor frequency and temperature. The similarity of the material to in vivo tissues, in terms of its biological and physical NMR characteristics, makes it an excellent tissue-equivalent substance, in addition to being an accurate calibration standard for routine MRI.

Quantitative magnetic resonance imaging in assessment of the blood-retinal barrier.

Application of magnetic resonance imaging (MRI) in two-dimensional quantitative assessment of blood-retinal barrier dysfunction was investigated in rabbits using a 0.1 T (4.25 MHz) resistive system. Reliable and consistent measurements of vitreous T1 were obtained repeatedly, in slices of width 5 mm and X-Y resolution of 1.2 mm. Calibration of reduction of T1 in eyes after injection of gadolinium-DTPA (Gd-DTPA) was performed, resulting in a dose-related response of relaxation rate (1/T1) to the dose of Gd-DTPA injected. Follow-up scans of injected eyes demonstrated a gradual spread of the T1 "hot-spot" as the contrast agent diffused through the vitreous. T1 rose gradually to basal levels by 72 hr. No local effect of Gd-DTPA was found by ophthalmoscopy. Xenon arc photocoagulation of rabbit retina reduced T1 from 1638 +/- 54 (n = 6, mean +/- SD) ms to 1408 +/- 118 (n = 4) msec (P less than 0.01) throughout the vitreous 5-7 hr after treatment. In treated rabbits receiving 1.0 mmol/l Gd-DTPA intravenously, T1 adjacent to lesions 90-120 min after injection was further reduced in a 63 microliter voxel to 670 +/- 50 ms (mean +/- SD, n = 5) with a minimum pixel value of 285 +/- 52 ms. It was estimated that this represented leakage into vitreous of 8.3 nmol Gd-DTPA. Plasma Gd-DTPA concentrations declined rapidly, with half-life of 20-40 min. The findings indicate that MRI is a technique with the potential for repeated quantitative three-dimensional assessment of blood-retinal barrier dysfunction.

Preparation of agarose gels as reference substances for NMR relaxation time measurement. EEC Concerted Action Program.

A standard method has been developed for the production of reference materials for NMR relaxation time measurement. These are based on agarose gels doped with gadolinium. The reproducibility and temporal stability of the gels have been found to be excellent. Electron microscope studies have shown good homogeneity. The relaxation behavior of such gels has been mathematically modeled with good agreement with experiment.

Multi-center trial with protocols and prototype test objects for the assessment of MRI equipment. EEC Concerted Research Project.

A trial was carried out in which the protocols and prototype test objects developed under a European Economic Community concerted research project for the assessment of MR imaging equipment were tested in a series of commercial imaging systems situated throughout Europe. In general, many imperfections were discovered in the imaging performance of the scanners and, in particular, the accuracy and precision with which the relaxation times T1 and T2 could be measured from the images were found to be rather disappointing.

Practical aspects of ghosting in resistive nuclear magnetic resonance imaging systems.

The concept of 'ghosting' in NMR images is discussed and it is demonstrated that, among other things, any external modulation of the NMR signal can produce such effects. A simple theoretical model, based on elementary Fourier modulation theory is presented for saturation recovery imaging sequences. Both amplitude (AM) and frequency (FM) modulations are considered. The predictions of the theory with regard to the positions and amplitudes of the ghosts produced by such modulations are outlined. Appropriate AM and FM conditions are generated experimentally on a 0.1 T resistive NMR system and measurements on the concomitant ghost images verify the theoretical predictions. Some practical implications of the phenomenon, with particular relevance to resistive magnet systems, are highlighted.

Principles of nuclear magnetic resonance (NMR)--current state of the art.

Nuclear magnetic resonance (NMR) imaging has progressed rapidly from laboratory curiosity to commercial exploitation and clinical application in the space of only three years. The physical principles underlying the technique are described and the equipment requirements outlined. The question of optimal magnetic field strength is discussed.