Evaluation of multiple-atlas-based strategies for segmentation of the thyroid gland in head and neck CT images for IMRT.

Segmenting the thyroid gland in head and neck CT images is of vital clinical significance in designing intensity-modulated radiation therapy (IMRT) treatment plans. In this work, we evaluate and compare several multiple-atlas-based methods to segment this structure. Using the most robust method, we generate automatic segmentations for the thyroid gland and study their clinical applicability. The various methods we evaluate range from selecting a single atlas based on one of three similarity measures, to combining the segmentation results obtained with several atlases and weighting their contribution using techniques including a simple majority vote rule, a technique called STAPLE that is widely used in the medical imaging literature, and the similarity between the atlas and the volume to be segmented. We show that the best results are obtained when several atlases are combined and their contributions are weighted with a measure of similarity between each atlas and the volume to be segmented. We also show that with our data set, STAPLE does not always lead to the best results. Automatic segmentations generated by the combination method using the correlation coefficient (CC) between the deformed atlas and the patient volume, which is the most accurate and robust method we evaluated, are presented to a physician as 2D contours and modified to meet clinical requirements. It is shown that about 40% of the contours of the left thyroid and about 42% of the right thyroid can be used directly. An additional 21% on the left and 24% on the right require only minimal modification. The amount and the location of the modifications are qualitatively and quantitatively assessed. We demonstrate that, although challenged by large inter-subject anatomical discrepancy, atlas-based segmentation of the thyroid gland in IMRT CT images is feasible by involving multiple atlases. The results show that a weighted combination of segmentations by atlases using the CC as the similarity measure slightly outperforms standard combination methods, e.g. the majority vote rule and STAPLE, as well as methods selecting a single most similar atlas. The results we have obtained suggest that using our contours as initial contours to be edited has clinical value.

Evidence for metabolic abnormalities in the muscles of patients with fibromyalgia.

Widespread muscle pain, fatigue, and weakness are defining characteristics of patients with fibromyalgia (FM). The aim of this review is to summarize recent investigations of muscle abnormalities in FM, which can be classified as structural, metabolic, or functional in nature. Histologic muscle abnormalities of membranes, mitochondria, and fiber type have been well described at both the light microscopic and ultrastructural levels. These structural abnormalities often correlate with biochemical abnormalities, defective energy production, and the resultant dysfunction of FM muscles. The observed abnormalities in FM muscles are consistent with neurologic findings and disturbances in the hypothalamic-pituitary-adrenal axis. Functional changes in FM muscles are assessed most directly by strength and endurance measurements, but pain and psychologic factors may interfere with accurate assessments. To compensate for diminished effort, the decreased efficiency of the work performance by patients with FM can be verified from P-31 magnetic resonance spectroscopy (MRS) data by calculation of the work/energy-cost ratio for various tasks. In the disease course, muscle abnormalities may be elicited by intrinsic changes within the muscle tissue itself and/or extrinsic neurologic and endocrine factors. The accurate assignment of intrinsic or extrinsic factors has been substantially clarified by a recent surge of experimental findings. Irrespective of the multifaceted causes of muscle dysfunction and pain, an in-depth understanding of the muscle defects may provide ideas for characterization of the underlying pathogenesis and development of new therapeutic approaches for fibromyalgia syndrome.

Muscle abnormalities in juvenile dermatomyositis patients: P-31 magnetic resonance spectroscopy studies.

OBJECTIVE: To characterize metabolic abnormalities in the muscles of children with the juvenile variant of dermatomyositis (JDM) by the use of noninvasive P-31 magnetic resonance spectroscopy (MRS). METHODS: Thirteen patients with JDM (ages 4-16 years) were studied. Biochemical status was evaluated with P-31 MRS by determining the concentrations of the high-energy phosphate compounds, ATP and phosphocreatine (PCr), ratios of inorganic phosphate (Pi) to PCr (Pi:PCr ratio), levels of free cytosolic ADP, and phosphorylation potentials (PPs) during rest, exercise, and recovery. RESULTS: Significant metabolic abnormalities were observed in the thigh muscles of 10 severely affected patients during rest, 2 graded levels of exercise, and recovery. Mean ATP and PCr levels in the muscles of JDM patients were 35-40% below the normal control values (P < 0.003). These data, along with elevated Pi:PCr ratios, higher ADP levels, and abnormal values for PPs, indicated defective oxidative phosphorylation in the mitochondria of diseased JDM muscles. MRS findings were normal in 2 additional patients who had improved with prednisone treatment and in 1 patient who had no muscle weakness (amyopathic variant of JDM). CONCLUSION: JDM patients can be monitored with noninvasive P-31 MRS without sedation. Biochemical defects in energy metabolism are concordant with the weakness and fatigue reported by JDM patients. Quantitative MRS data are useful for evaluating patients and optimizing drug treatment regimens.