Comparison of QCT-derived and DXA-derived areal bone mineral density and T scores

Two-dimensional areal bone mineral density (aBMD) of the proximal femur measured by three-dimensional quantitative computed tomography (QCT) in 91 elderly women was compared to dual-energy X-ray absorptiometry (DXA) aBMD results measured in the same patients. The measurements were highly correlated, though QCT aBMD values were marginally lower in absolute units. Transformation of the QCT aBMD values to T score values using National Health and Nutrition Examination Survey (NHANES) DXA-derived reference data improved agreement and clinical utility.

INTRODUCTION

World Health Organization guidelines promulgate aBMD (g cm(-2)) measurement of the proximal femur for the diagnosis of bone fragility. In recent years, there has been increasing interest in QCT to facilitate understanding of three-dimensional bone structure and strength.

OBJECTIVE

To assist in comparison of QCT-derived data with DXA aBMD results, a technique for deriving aBMD from QCT measurements has been developed.

METHODS

To test the validity of the QCT method, 91 elderly females were scanned on both DXA and CT scanners. QCT-derived DXA equivalent aBMD (QCT(DXA) aBMD) was calculated using CTXA Hip software (Mindways Software Inc., Austin, TX, USA) and compared to DXA-derived aBMD results.

RESULTS

Test retest analysis indicated lower root mean square (RMS) errors for CTXA; F test between CTXA and DXA was significantly different at femoral neck (FN) and trochanter (TR) (p < 0.05). QCT underestimates DXA values by 0.02 +/- 0.05 g cm(-2) (total hip, TH), 0.01 +/- 0.04 g cm(-2) (FN), 0.03 +/- 0.07 g cm(-2) (inter-trochanter, IT), and 0.02 +/- 0.05 g cm(-2) (TR). The RMS errors (standard error of estimate) between QCT and DXA T scores for TH, FN, IT, and TR were 0.36, 0.40, 0.39, and 0.49, respectively.

CONCLUSIONS

This study shows that results from QCT aBMD appropriately adjusted can be evaluated against NHANES reference data to diagnose osteoporosis.

A comparison of the disposable Ambu�AuraOnce?Laryngeal Mask with the reusable LMA Classic?laryngeal mask airway

Single-use supraglottic airway devices are now available and are intended to be comparable with the reusable LMA Classic laryngeal mask airway. We performed a randomised cross-over study comparing the Ambu AuraOnce Laryngeal Mask with the LMA Classic. Fifty patients participated in the trial. Success rates for insertion at the first attempt were similar (92% with the Ambu and 84% with the LMA Classic; p = 0.22). The volumes of air required to inflate the cuff to produce a seal were similar, but the cuff pressure was lower for the Ambu Laryngeal Mask (median (IQR [range]) 18 (10-31 [0-100] cmH(2)O) than the LMA Classic 27 (17-50 [4-90] cmH(2)O; p = 0.007). Visual analogue scores for ease of insertion were 87 (73-93 [26-97]) mm for the Ambu and 84 (60-89 [18-96]) for the LMA Classic (p = 0.017). Complications were similar in both groups. We suggest that the disposable Ambu Laryngeal Mask is an acceptable alternative to the reusable LMA Classic.

Predictive value of IL-18 and SC5b-9 for neurocognitive dysfunction after cardiopulmonary bypass

BACKGROUND

Neurological injury after cardiopulmonary bypass (CPB) continues to be a major problem after cardiac surgery. The aim of this study was to investigate the predictive value of Interleukin-18 (IL-18) and SC5b-9 as biochemical markers of neurocognitive dysfunction after cardiac surgery.

METHODS

A total of 30 patients undergoing elective cardiac surgery using CPB were recruited. Blood samples were obtained for IL-18 and SC5b-9 concentrations before induction, 24, 48, 72, 96 and 120 h post-CPB and 6 weeks after operation. In addition, patients underwent a standard battery of neuropsychometric tests before operation and at day 5 and 6 weeks after operation.

RESULTS

Serum concentration of IL-18, but not SC5b-9, was significantly different between patients with and without neurocognitive dysfunction; serum IL-18 concentration significantly increased in patients with neurocognitive dysfunction (P = 0.018). Neurological outcome was significantly dependent on peak difference in IL-18 concentration at day 5 (P = 0.033), but not on peak difference in SC5b-9 concentration (P = 0.16). Eight patients had neurocognitive dysfunction at day 5 and three had neurocognitive dysfunction at 6 weeks. In a very small number of patients, no significant association was demonstrated between IL-18 or SC5b-9 concentrations and neurocognitive dysfunction at 6 weeks.

CONCLUSIONS

IL-18 has the potential as a useful marker of neurological dysfunction, requiring further investigation.

The pressure required to force liquid through breathing system filters*

Liquid in the form of sputum and condensation may be forced through a breathing system filter if sufficient pressure is applied to the filter layer, with the potential for cross-infection. Twenty-three different breathing system filters (12 adult, 11 paediatric) were assessed to determine the pressure causing liquid penetration. Five samples of each were tested by connecting the ventilator end of a breathing system filter to a water-filled U-tube and reservoir. The reservoir was positioned so that the water surface was level with the filter layer and raised until liquid appeared through the filter layer on the patient side and the water-column height recorded. There were substantial differences in performance between models. Liquid penetration occurred at lower pressures for adult electrostatic than adult pleated filters: median [IQR] 1.18 [1.08- 1.32] and 8.04 [4.27-12.80] kPa, respectively, p < 0.0001. Liquid penetration occurred at similar pressures in paediatric electrostatic filters (0.98 [0.74-1.32] kPa) compared to adult electrostatic filters.

Unwanted effects of morphine-6-glucoronide and morphine

The active metabolite of morphine, morphine-6-glucuronide (M6G), may have fewer unwanted effects than morphine. We randomly allocated 144 women to receive either M6G or morphine as part of general anaesthesia for day case gynaecological laparoscopy. The incidence of nausea, vomiting, pain, sedation and skin rash, and severity of nausea, pain and sedation after surgery were recorded by direct observation in hospital, and by questionnaire until the next morning. Compared with the M6G group, patients who received morphine were more likely to report nausea in the first 2 h after surgery (odds ratio 2.9, CI 1.31-6.21) and to suffer it with greater severity. During the same time period, they were more likely to vomit and feel sleepy, but the intensity of pain and use of rescue analgesics were similar in both groups. The incidences of nausea, vomiting and the feeling of sleepiness continued to be greater in the morphine group during and after the journey home. The next morning, patients in the morphine group remained sleepier, but the incidence of nausea was similar for the two groups. M6G appears to have a better toxicity profile than morphine. More efficacy studies are needed to define accurately the analgesic potency of systemically administered M6G.

Regulation of plasma osteocalcin by corticosterone and norepinephrine during restraint stress

Osteocalcin (OC), an extracellular calcium-binding protein of bone origin, is synthesized by osteoblasts and binds with high specificity to bone mineral crystals. A small, but relatively consistent portion of newly synthesized OC which is released to circulation has been well correlated with histological indices of osteoblastic activity. Synthesis of OC is regulated by numerous hormones including glucocorticoids. We previously reported that mild mental stressors such as cage change or cold exposure decreased rat plasma OC by up to 40% within 1 h. A similar response was induced in a time- and dose-related manner by injection of physiological levels of corticosterone (CS), the active glucocorticoid in rats. Prone immobilization by foot restraint of conscious rats for up to 2 h (IMMO) is a well-characterized model of classic "fight-or-flight" response. This model induces an immediate and prolonged elevation of CS, as well as the catecholamines epinephrine (E) and norepinephrine (NE). In marked contrast to milder stressors, immobilization induced an immediate increase of plasma OC, greater than 50% within 5-20 min, which returned toward normal after 2 h of restraint. Selective ablation of the hormones by adrenal medulectomy, adrenalectomy, or blockade of sympathetic ganglia did not abolish the initial rapid rise of plasma OC. Even before IMMO, plasma OC was increased by about 50% in the absence of sympathetic neural function or adrenal CS production. The presence of both CS and NE, but not E, was required to return plasma OC concentrations to basal levels. This strongly suggests interaction of CS and NE to regulate plasma OC and its release from bone. As expected, prior cold exposure lowered plasma OC, but did not abolish a subsequent increase in response to IMMO, nor did IMMO repeated daily for 7 days. The stimulus for the initial rapid elevation of OC is unknown, but likely to be of importance in the role OC plays in response to stress. Further investigation of the OC under mental stress should help to understand the function of this abundant and highly conserved bone protein.

The state of human bone tissue during space flight

The results of studying the bone tissue of cosmonauts after the flights (4-8 month) have been compared to the data of investigating the healthy individuals during head-down tilt (HDT, 370 days). Noninvasive methods (computer tomography, gammaphoton absorptiometry) revealed a decrease in the vertebral spongy mineral density or a increase of this parameter by a similar magnitude versus the individual preflight values in some cosmonauts. During studies of clinical cases of osteoporosis it was shown that the vertebral mineral density ratios and presence or absence of vertebral compression fractures in different age groups are nonequal.

[The state of bone tissue in monkeys in experiments in the Cosmos-1887 biosatellite]

Using invasive and noninvasive techniques, we studied bone changes in primates flown for 13 days on Cosmos-1887 and compared them with the data obtained from vivarium control animals and from the flown primates that were after flight exposed to a ground-based synchronous experiment in the biosatellite mockup. It was found that bone density in the diaphysis of the tibia decreased while its growth rate remained unchanged or diminished. Contact X-raying indicated a higher rate of endosteal resorption in the flown primates when compared with the controls. Histomorphometric measurements of iliac bioptates displayed signs of inhibited bone formation after flight. The above observations are discussed and compared with the results obtained in previous biosatellite flights and ground-based studies.

[Study of the musculoskeletal system of the spine in humans after long-term space flights by the method of computerized tomography]

By computer tomography, mineral density of lumbar vertebrae and their segments as well as back muscle (++ilio-costal, extensor and ++inter-spinal) density and mass were measured in four Salyut-7 crewmembers before and after extended flights (of 5 and 7 months in duration). These findings are in good agreement with the results of prolonged bed rest studies in which trabecular bone of vertebral bodies was investigated: mineral density diminished only in some (approximately 10%) of the test subjects. At the same time mineral density loss was seen in the vertebral elements where muscles were attached. Also, muscle mass was reduced. It is emphasized that the level of changes was not correlated with flight time. Further investigations in this area are discussed.

A preliminary study of MRI quantification of simulated calcified pulmonary nodules

The potential of magnetic resonance imaging (MRI) quantification of calcium for the evaluation of pulmonary nodules was investigated in simulated nodules. Calcium salts do not contain mobile protons and thus have no signal on MR proton images. To determine whether the absence of signal from partially calcified nodules could be quantified, we studied simulated nodules containing known quantities of calcium salts. The soft tissue equivalent material was an agar-gelatin mixture (T1:1100-1500 msec; T2: 59-62 msec). In the first experiments, glass tubes were filled with the mixture, which contained suspensions of calcium carbonate (CaCO3) or silica dioxide (Si02), and were subjected to computed tomography (CT) scanning and MR imaging. In a second series of studies CaCO3 particles of various sizes (and therefore different surface-to-volume ratios) were similarly suspended and subjected to CT scanning and MR imaging. In a third series hydroxyapatite (HA) suspensions of different sizes were similarly studied. CaCO3 produced a significant reduction in MR hydrogen density and signal intensity of the agar-gelatin mixture. Reduction in T1 and T2 relaxation times was inconsistent and not related to particle size. CaCO3 produced its effect by soft-tissue displacement. HA (and Si02) caused a more marked fall in MR hydrogen density, signal intensity, and T1 and T2 relaxation times. The degree of the T1 and T2 effects was related to particle size, indicating a hydrophilic surface effect. The authors conclude that MRI quantification of calcium within pulmonary nodules (or other tissues) will be complex and will relate to the precise composition of the calcium salt and to the particle size of the aggregates.

Evaluation of a chest phantom for CT nodule densitometry

The characteristics of a chest phantom used for CT nodule densitometry were determined by use of a GE CT 9800 scanner (General Electric, Milwaukee, WI). The supplied reference rods were scanned in different positions within the lung fields of the phantom and with varied chest wall thicknesses. The liver/spleen inserts were added. The CT attenuation values of different-size rods and their mineral content were also tested. The size of the standard rod is the major determinant of its CT number, which varied from 1 to 83 H. The standard rods contained no measurable calcium or other mineral. Position-dependent variability in CT numbers was relatively small with the GE CT 9800 scanner. The simulated chest wall additions and liver/spleen inserts produced only small increases in CT density. We conclude that the GE CT 9800 scanner, as an example of one of the newer CT scanners, shows improved operating characteristics for pulmonary nodule densitometry. Nodule densitometry should be further evaluated with simplified phantoms.

Dynamic CT scanning of the normal canine liver: interpretation of time density curves resulting from an intravenous bolus injection of contrast material

Seven adult male mongrel dogs were monitored by electromagnetic flow probes and string occluders around the hepatic artery and portal vein. Then, time density curves of the liver, aorta and portal vein were recorded using dynamic CT scanning following the bolus injection of contrast material into a peripheral vein (n = 7) and a mesenteric vein branch (n = 5). Information on total hepatic blood flow could not be obtained from the mesenteric vein injection. The hepatic time density curve could, however, be broken into its two components, hepatic arterial and portal venous flow contribution, by selective ligation of the hepatic artery or portal vein. It could be demonstrated that the arterial component of liver enhancement reached its peak at the end of the aortic wash-out of contrast material. Thus, the hepatic time-density curve could be broken in its two components by superimposing the aortic time density curve onto the hepatic curve. An attempt was made to estimate relative portal venous blood flow by using the slopes or the peaks of both components of the hepatic curve. Using the slopes of the hepatic curve resulted in a consistent underestimation of portal venous blood flow, whereas the peaks gave an estimate of portal venous flow with an accuracy within +/- 8%.

Bone disease in alcohol abuse

We evaluated bone disease in eight white men between the ages of 49 and 61 years who had been abusing alcohol for at least 10 years. The mean density of vertebral cancellous bone was 58% of normal, whereas the mean density of appendicular cortical bone was 90% of normal. Marked reduction in active bone resorption and bone formation was seen without evidence of osteomalacia. Serum levels of calcium and magnesium were in the lower range of normal; serum levels of phosphorus, calcifediol, and calcitriol were normal; and serum levels of parathyroid hormone and nephrogenous cyclic adenosine monophosphate were in the higher range of normal. These data suggest that bone disease in these subjects is not due to inhibition of parathyroid hormone secretion or function, or abnormal vitamin D metabolism, but to an inhibition of bone remodeling by a mechanism independent of the calciotropic hormones.

Attenuation changes of the normal and ischemic canine kidney. Dynamic CT scanning after intravenous contrast medium bolus

The potential of CT scanning to explore total and regional renal blood flow was evaluated in a dog model with unilateral renal artery stenosis (n = 7, reduction of renal blood flow: 32-75% of base line flow). Attenuation versus time curves were generated for the renal cortex and medulla, as well as for the aorta and renal vein. A fast CT scanner was used which allowed for up to 24 scans/minute at the same level (slice thickness: 10 mm). A total of 10 ml contrast medium was injected into a peripheral vein for each scan series taken. During baseline conditions, the curve of the renal cortex and medulla demonstrated 2 peaks. The first peak was mainly related to early vascular enhancement, whereas the second peak corresponded mainly to the appearance of contrast medium in the distal convolutes and collecting ducts. Ischemia of the kidney resulted in a reduction of the first peak and a flattening of the leading edge slope. Transport of contrast medium through the extravascular compartments of the kidney was delayed during ischemia. Relative renal blood flow was obtained from the CT data by dividing peak enhancement by rise-time as assessed from the cortical curve. All measurements were related to baseline flow and validated by flow measurements using radioactive labeled microspheres (n = 5). Correlation was found to be r = 0.97.

Menstrual function and bone mass in elite women distance runners. Endocrine and metabolic features

Bone mass and metabolic features were studied in 17 women distance runners. Eleven of the women had secondary amenorrhea for 1 to 7 years. Six women have maintained regular menses since menarche. Both groups were matched for aerobic capacity, body fat, exercise intensity, and age of menarche. Mineral density of lumbar spine in the amenorrheic runners was lower than that in the cyclic women and age-matched controls, but higher than that in runners with secondary amenorrhea who are less physically active. Mineral density of the radius was normal in both groups. Running-related fractures were more frequent in amenorrheic women. Metabolic assessment showed no differences between groups, except that serum triiodothyronine was lower in the amenorrheic group, perhaps reflecting low calorie intake. Intense exercise may reduce the impact of amenorrhea on bone mass; however, amenorrheic runners remain at high risk for exercise-related fractures.

Assessment of human right ventricular cast volume by CT and angiocardiography

Angiocardiographic methods available for cardiac chamber volume measurements have been shown to be less accurate although more practical than CT for the evaluation of the LV. To explore the capability of CT for RV volume measurements, silastic casts of seven normal RV were measured by a displacement method, conventional angiocardiographic biplane methods, and CT. The displacement method used degassing beneath vacuum to remove air trapped in the casts, and the actual volumes, which varied between 62 and 188 cc, were measured by Archimedes' principle. Cast volumes measured by biplane angiogram methods displayed a varying degree of spread around the regression line, caused by the chamber's irregular shape and its variation in orientation relative to the x-ray beams. CT measurements were in all aspects significantly more accurate.

[Imaging of blood flow-dependent curve parameters in the course of sequential computed tomography of the kidneys following intravenous injection of a contrast bolus]

Since the introduction of fast CT scanners with short scanning times the early density changes observed during the first transit of a contrast bolus can be clearly demonstrated and quantified. A theoretical curve can be fit to the CT data describing the density changes in the kidney according to the indicator dilution principle. A curve parameter can be obtained which characterizes the shape of the curve. Then an image can be calculated which reflects the selected curve parameter rather than tissue densities. Such images have been termed "functional images". Using this type of imaging we were able to demonstrate acute changes in renal perfusion.

Noninvasive measures of bone bending rigidity in the monkey (M. nemestrina)

The in vivo bending rigidity and bone mineral content of monkey ulnae and tibiae were measured. Bending rigidity in the anteroposterior plane was measured by an impedance probe technique. Forced vibrations of the bones were induced with an electromechanical shaker, and force and velocity at the driving point were determined. The responses over the range of 100-250 Hz were utilized to compute the bending rigidity. Bone mineral content in the cross section was determined by a photon absorption technique. Seventeen male monkeys (Macaca nemestrina) weighing 6-14 kg were evaluated. Repeatability of the rigidity measures was 4%. Bone mineral content was measured with a precision of 3.5%. Bending rigidity was correlated with the mineral content of the cross section, r = 0.899. Two monkeys were evaluated during prolonged hypodynamic restraint. Restraint produced regional losses of bone most obviously in the proximal tibia. Local bone mineral content declines 17 to 24% and the average bending rigidity declines 12 to 22%. Changes in bones leading to a reduction in mineral content and stiffness are discussed.