Automated characterization of multiple alpha peaks in multi-site electroencephalograms.

The identification of alpha rhythm in the human electroencephalogram (EEG) is generally a laborious task involving visual inspection of the spectrum. Moreover the occurrence of multiple alpha rhythms is often overlooked. This paper seeks to automate the process of identifying alpha peaks and quantifying their frequency, amplitude and width as a function of position on the scalp. Experimental EEG was fitted with parameterized spectra spanning the alpha range, with results categorized by multi-site criteria into three distinct classes: no distinguishable alpha peak, a single alpha peak, and two alpha peaks. The technique avoids visual bias, integrates spatial information, and is automated. We show that multiple alpha peaks are a common feature of many spectra.

Reduced bone mineral density in patients with adult onset growth hormone deficiency.

We have demonstrated previously that adults with isolated GH deficiency of childhood onset have a reduced bone mineral density (BMD) of vertebral trabecular bone [quantitative computed tomography (QCT): median Z score -1.3, P < 0.01, n = 12] and of cortical bone in the forearm [single photon absorptiometry (SPA): median Z score -2.9, P = 0.001, n = 7]. We have now examined BMD in 26 patients (13 men, 13 women), aged between 23.6 and 59.5 (mean 42.4) yr, with adult onset GH deficiency, defined as a GH response of less than 5 micrograms/L to provocative testing, of at least two years duration. BMD was measured using QCT for vertebral trabecular bone, dual energy x-ray absorptiometry (DXA) in the lumbar spine and femoral neck, and SPA in the forearm. There was a highly significant reduction in QCT (median Z score -1.07, P < 0.00005), in DXA of the lumbar spine (median Z score -0.76, P = 0.0001) and in SPA of the forearm (median Z score -0.86, P = 0.0001) but not in DXA of the femoral neck (median Z score -0.38, P = 0.35). There were no significant differences in Z scores between those patients with isolated GH deficiency and those with GH and gonadotrophin deficiency. There was a significant positive correlation between age at which BMD was measured and Z score (the older the patient, the higher the Z score) for QCT (r = 0.38, P < 0.05) and SPA (r = 0.48, P < 0.01) with a trend to a positive correlation for DXA of the lumbar spine and femoral neck. Patients were grouped according to estimated duration of GH deficiency (less than 5 yr, n = 7; 5-10 yr, n = 10; greater than 10 yr, n = 9). These groups did not show a significant difference in BMD at any site. We conclude that patients with adult onset GH deficiency (isolated or in conjunction with other pituitary hormone deficiencies) have a reduced BMD. Age at development of GH deficiency may be more important than duration of GH deficiency in determining the degree of reduction in bone mass. The impact of GH treatment on BMD in adults with adult onset GH deficiency requires investigation.

Increased bone density after recombinant human growth hormone (GH) therapy in adults with isolated GH deficiency.

The physiological role of GH in the adult skeleton is unknown. In this study, 12 adults (10 males and 2 females) with isolated GH deficiency were treated with GH as a single daily sc injection (0.125 IU/kg.week for the first 4 weeks and subsequently at 0.25 IU/kg.week) for 1 yr in a double blind, placebo-controlled manner. Bone mineral density of the spine (T12-L3) was measured by quantitative computed tomography, and bone mineral content (BMC) of the forearm by single photon absorptiometry at entry into the study and subsequently at 6 monthly intervals. All baseline bone mineral measurements were reduced compared with those in an age- and sex-matched control population. In the treatment cohort, quantitative computed tomography spinal trabecular bone mineral density increased by 7.8 g/L after 6 months of GH replacement (mean +/- SEM, 151.7 +/- 6.0 vs. 159.5 +/- 5.9 g/L; n = 11; P < 0.01), and this increment was maintained at 1 yr (160.7 +/- 6.3 g/L). Proximal forearm (cortical) BMC showed no change after 6 months of GH replacement, but there was a significant increase of 0.06 g/cm after 12 months of GH replacement (from 1.38 +/- 0.04 to 1.44 +/- 0.04 g/cm; n = 12; P < 0.05). Distal forearm (cortical and trabecular) BMC also increased significantly during the study period from 1.46 +/- 0.04 g/cm to 1.52 +/- 0.05 g/cm; n = 12, P < 0.05. No significant changes occurred in bone mineral measurements during 6 months of placebo therapy. Midthigh muscle and fat cross-sectional area increased and decreased, respectively, during the active treatment phase. These results demonstrate that GH plays an important role in maintaining the integrity of the adult skeleton.

Neurophysical modeling of brain dynamics.

A recent neurophysical model of brain electrical activity is outlined and applied to EEG phenomena. It incorporates single-neuron physiology and the large-scale anatomy of corticocortical and corticothalamic pathways, including synaptic strengths, dendritic propagation, nonlinear firing responses, and axonal conduction. Small perturbations from steady states account for observed EEGs as functions of arousal. Evoked response potentials (ERPs), correlation, and coherence functions are also reproduced. Feedback via thalamic nuclei is critical in determining the forms of these quantities, the transition between sleep and waking, and stability against seizures. Many disorders correspond to significant changes in EEGs, which can potentially be quantified in terms of the underlying physiology using this theory. In the nonlinear regime, limit cycles are often seen, including a regime in which they have the characteristic petit mal 3 Hz spike-and-wave form.

Enlargement of the tensor intermuscularis muscle in Graves' ophthalmopathy. A computed tomographic and magnetic resonance imaging study.

OBJECTIVE: To determine whether the tensor intermuscularis muscle (TIM), which consists of muscle fibers in the superolateral intermuscular orbital septum, is involved in Graves' ophthalmopathy (GO). DESIGN: The computed tomographic (n = 24) and magnetic resonance imaging (n = 10) appearances of the TIM were retrospectively examined in 34 patients with known GO. The severity of GO was assessed by applying a scoring system from 0 to 3 (ie, normal [0], mild [1], moderate [2], and severe [3]) to each of the rectus muscles and superior oblique muscle. The severity of exophthalmos, enlargement of the superior ophthalmic vein, and displacement of the lacrimal gland were also recorded. RESULTS: The TIM appeared as thickening of the septum immediately behind the globe, and it was best seen on coronal magnetic resonance images. There was enlargement of the TIM in 19 of the 34 patients, and it was bilateral in 17. Enlargement was present only in patients with moderate or severe involvement of other muscles (muscle index, > 7/15), and it was significantly correlated with the muscle index (P < .05), exophthalmos (P < .05), enlargement of the superior ophthalmic vein (P < .005), and anterior displacement of the lacrimal gland (P < .01). Severe enlargement of the TIM was seen in only five of the 34 patients, and it showed a close correlation with the muscle index (P < .005), exophthalmos (P < .001), enlargement of the superior ophthalmic vein (P < .001), and anterior displacement of the lacrimal gland (P < .001). CONCLUSIONS: Enlargement of the TIM in GO can be identified on computed tomographic and magnetic resonance imaging scans. It is invariably associated with moderate or severe involvement of other extraocular muscles, and it correlates closely with other well-recognized imaging features of severe GO.

Prediction of enophthalmos by computed tomography after 'blow out' orbital fracture.

In 11 patients with blow out fracture of the orbit, measurement of orbital volume using computed tomography (CT) more than 20 days after injury correlated well with enophthalmos measured from the same scans (r = 0.87, p < 0.001, SEE 0.63 mm), with a 1 cm3 increase in orbital volume causing 0.8 mm of enophthalmos. This confirms the cause of enophthalmos after blow out fracture to be increase in orbital volume rather than fat atrophy or fibrosis. In a further 25 patients scanned within 20 days of injury the degree of enophthalmos was less marked than would be predicted from the orbital volume measurement. This was probably because of the presence of oedema, haemorrhage, or both behind the globe which would prevent immediate development of enophthalmos. CT measurement of orbital volume within 20 days of injury may predict the final degree of enophthalmos and identify those patients at risk of late enophthalmos, allowing appropriate early surgical intervention.

Orbital volume measurement in the management of pure blowout fractures of the orbital floor.

With the recent advent of accurate orbital volume assessment by computed tomography, a retrospective analysis was made of 31 patients with 'pure' blowout fracture of the orbital floor, managed either surgically or conservatively, to determine whether orbital volume measurement could provide an additional parameter of use in the management of such fractures. There was a significant difference in orbital volume discrepancy between patients managed surgically or conservatively suggesting that this investigation may be of use in decision making on surgical intervention in patients with orbital blowout fractures.

Computed tomography attenuation measurements for the characterization of hepatic haemangiomas.

The attenuation values of 21 hepatic haemangiomas in 19 patients were measured on non-enhanced computed tomographic (CT) scans and compared with the attenuation of adjacent liver and the inferior vena cava (IVC). The attenuation of hepatic haemangiomas was lower than that of the surrounding liver, but there was no correlation between these two measurements. There was a highly significant correlation between the attenuation of haemangiomas and blood in the vena cava (r = 0.905, p less than 0.001). All the haemangiomas had attenuations within 7 HU of caval blood. By comparison, in 34 hypodense hepatic lesions that did not show contrast-enhanced appearances characteristic of haemangioma, there was no significant correlation between the attenuation of the lesions and the IVC. Nineteen (56%) of these lesions had attenuations differing more than 7 HU from that of caval blood. The influence of this observation on the requirement for dynamic contrast-medium-enhanced and delayed post-contrast CT in the assessment of hepatic lesions is discussed.

Contrast-enhanced computed tomography of the normal and abnormal gallbladder.

One hundred and fourteen upper abdominal computed tomography examinations performed before and after intravenous contrast were reviewed. In 48 patients who had no evidence of biliary or pancreatic disease, the mean gallbladder wall attenuation before contrast was 25 +/- 13 HU and after contrast 42 +/- 18 HU, with a wall thickness of 1.9 +/- 0.43 mm. In 14 patients with chronic pancreatitis these values were 24 +/- 10.5 HU, 44 +/- 25 HU and 2.0 +/- 0.54 mm, respectively. In a further group of 15 patients with chronic biliary disease, the values were 34 +/- 15 HU, 53 +/- 18 HU and 2.3 +/- 0.9 mm. The degree of wall enhancement was statistically significant in each group. There was no statistical difference in the attenuation characteristics or wall enhancement between normal patients and those with chronic pancreatitis. Patients with chronic biliary disease had a thicker gallbladder wall with higher attenuation before contrast but a similar degree of enhancement.

Low-dose computed tomographic imaging in orbital trauma.

We review the findings in 75 computed tomographic (CT) examinations of 66 patients with orbital trauma who were imaged using a low-radiation-dose CT technique. Imaging was performed using a dynamic scan mode and exposure factors of 120 kVp and 80 mAs resulting in a skin dose of 11 mGy with an effective dose-equivalent of 0.22 mSv. Image quality was diagnostic in all cases and excellent in 73 examinations. Soft-tissue abnormalities within the orbit including muscle adhesions were well demonstrated both on primary axial and reconstructed multiplanar images. The benefits of multiplanar reconstructions are stressed and the contribution of soft-tissue injuries to symptomatic diplopia is examined.

Application of computer texture analysis to the Singh Index.

The Singh Index, which describes trabecular patterns in the proximal femur, has been used as a predictor for hip fractures and as an indicator of osteopenia. Evidence suggests that its contribution to the assessment of hip fracture risk is in its description of the structural properties of the femur. However, subjectivity in its determination may limit its practical value. In this study, we have used computer texture analysis to characterize the textural changes in trabecular bone which occur in osteoporosis. Texture analysis of the proximal femur was used to rank radiographs of 25 cadaver femora by Singh grading. These rankings were compared with those performed by two experienced radiologists. The computer method performed better than the least consistent individual radiologist, but not as well as the two radiologists in combination. The method required no radiologist's time after the system had been 'trained' from a set of example radiographs. The method has potential for use in large studies in which speed and consistency of measurement are important.

The influence of chemical shift artifact on magnetic resonance imaging of the ligamentum flavum at 0.5 tesla.

STUDY DESIGN: Retrospective clinical magnetic resonance imaging study and prospective magnetic resonance imaging volunteer study of the appearance of the ligamentum flavum. OBJECTIVE: To demonstrate the effect of chemical shift artifact on the apparent thickness of the ligamentum flavum on axial magnetic resonance images. SUMMARY OF BACKGROUND DATA: The ligamentum flavum is a symmetric structure clearly seen on magnetic resonance images. Apparent unilateral thickening may be interpreted as indicating a pathologic process, and the influence of chemical shift artifact on the apparent thickness of the ligamentum flavum has not been emphasized. METHODS: Ligamenta flava thicknesses were measured from axial T1-weighted gradient echo magnetic resonance scans of 12 consecutive patients and various axial sequences in seven volunteers. RESULTS: The ligamentum flavum appeared consistently thicker on the lower side of the readout gradient field. This chemical shift effect could be manipulated by swapping phase and frequency or patient orientation in the magnet. CONCLUSIONS: Caution should be applied in attributing apparent asymmetry of the ligamenta flava to disease; the influence of chemical shift artifact should be considered.

Nonuniform corticothalamic continuum model of electroencephalographic spectra with application to split-alpha peaks.

Recent theoretical work has successfully predicted electroencephalographic spectra from physiology using a model corticothalamic system with spatially uniform parameters. The present work incorporates parameter nonuniformities into this model via the coupling they induce between spatial eigenmodes. Splitting of the spectral alpha peak, an effect seen in a small percentage of the normal population, is investigated as an illustrative special case. It is confirmed that weak splitting can arise from mode structure if the peak is sufficiently sharp, even for uniform parameters. However, it is further demonstrated that greater splitting can result from nonuniformities, and it is argued that this mechanism for split alpha is better able to account quantitatively for this effect than previously suggested alternatives of pacemakers or purely cortical resonances. On introducing nonuniformities in corticothalamic loop time delays, we find that the alpha frequency also varies as one moves from the front to the back of the head, in accord with observations, and that analogous (but less distinct) variations are seen in the beta peak. Analysis shows realistic variations of around +/-10 ms relative to the mean loop delay of approximately 80 ms can account for observed splittings of about 1 Hz. It is also suggested that subjects who display clear alpha splitting form the tail of a distribution of magnitude of cortical inhomogeneity, rather than a separate population.

Lower extremity and pelvic stress fractures in athletes.

Stress fractures occur following excessive use and are commonly seen in athletes, in whom the lower limbs are frequently involved. Delayed diagnosis and management of these injuries can result in significant long-term damage and athlete morbidity. A high index of suspicion may facilitate diagnosis, but clinical presentation may be non-specific. In this regard, imaging in the form of plain radiograph, CT, MRI and bone scintigraphy may be of value. This article reviews the incidence, presentation, radiological findings and management options for athletes with stress fractures of the lower limb.