Optimization of chest CT protocols based on pixel image matrix, kernels and iterative reconstruction levels - A phantom study.

INTRODUCTION: This study investigated the impact of high matrix image reconstruction in combination with different reconstruction kernels and levels of iterative reconstructions on image quality in chest CT. METHODS: An anthropomorphic chest phantom (Kyoto Kagaku Co., Ltd., Kyoto, Japan), and a Catphan® 600 (The Phantom Laboratory, Greenwich, NY, USA) phantom were scanned using a dual source scanner. Standard institutional protocol with 512 × 512 matrix was used as a reference. Reconstructions were performed for 768 × 768 and 1024 × 1024 matrices and all possible combinations of three different kernels and five levels of iterative reconstructions were included. Signal difference to noise ratio (SdNR) and line pairs per cm (lp/cm) were manually measured. A Linear regression model was applied for objective image analysis (SdNR) and inter-and intra-reader agreement was given as Cohen's kappa for the visual image assessment. RESULTS: Matrix size did not have a significant impact on SdNR (p = 0.595). Kernel (p = 0.014) and ADMIRE level (p = 0.001) had a statistically significant impact on SdNR. The spatial resolution ranged from 7 lp/cm to 9 lp/cm. The highest spatial resolution was achieved using kernel Br64 and ADMIRE 1, 2 and 3 in both 768- and 1024-matrices, and with Br59 with ADMIRE 2 and 4 and 768-matrix, all visualizing 9 lp/cm. Both readers scored kernel Br59 highest, and the scoring increased with increasing levels of Iterative Reconstruction. CONCLUSION: Matrix size did not influence image quality, however, the choice of kernel and degree of IR had an impact on objective and visual image quality in 768 - and 1024-matrices, suggesting that increased degree of IR may improve diagnostic image quality in chest CT. IMPLICATIONS FOR PRACTICE: Image quality in CT of the lung may be improved by increasing the level of IR.

Accuracy of methods for reporting inorganic element concentrations and radioactivity in oil and gas wastewaters from the Appalachian Basin, U.S. based on an inter-laboratory comparison.

Accurate and precise analyses of oil and gas (O&G) wastewaters and solids (e.g., sediments and sludge) are important for the regulatory monitoring of O&G development and tracing potential O&G contamination in the environment. In this study, 15 laboratories participated in an inter-laboratory comparison on the chemical characterization of three O&G wastewaters from the Appalachian Basin and four solids impacted by O&G development, with the goal of evaluating the quality of data and the accuracy of measurements for various analytes of concern. Using a variety of different methods, analytes in the wastewaters with high concentrations (i.e., >5 mg L-1) were easily detectable with relatively high accuracy, often within ±10% of the most probable value (MPV). In contrast, often less than 7 of the 15 labs were able to report detectable trace metal(loid) concentrations (i.e., Cr, Ni, Cu, Zn, As, and Pb) with accuracies of approximately ±40%. Despite most labs using inductively coupled plasma mass spectrometry (ICP-MS) with low instrument detection capabilities for trace metal analyses, large dilution factors during sample preparation and low trace metal concentrations in the wastewaters limited the number of quantifiable determinations and likely influenced analytical accuracy. In contrast, all the labs measuring Ra in the wastewaters were able to report detectable concentrations using a variety of methods including gamma spectroscopy and wet chemical approaches following Environmental Protection Agency (EPA) standard methods. However, the reported radium activities were often greater than ±30% different to the MPV possibly due to calibration inconsistencies among labs, radon leakage, or failing to correct for self-attenuation. Reported radium activities in solid materials had less variability (±20% from MPV) but accuracy could likely be improved by using certified radium standards and accounting for self-attenuation that results from matrix interferences or a density difference between the calibration standard and the unknown sample. This inter-laboratory comparison illustrates that numerous methods can be used to measure major cation, minor cation, and anion concentrations in O&G wastewaters with relatively high accuracy while trace metal(loid) and radioactivity analyses in liquids may often be over ±20% different from the MPV.

Hypertension, creatinine, and plasma renin activity in heart transplant recipients.

Development of de novo hypertension in a large proportion of orthotopic heart transplant recipients receiving cyclosporine has previously been reported. This hypertension is characterized by a persistence of increased peripheral resistance, sodium retention, and loss of nocturnal decline in BP. Vascular nephropathy with plasma renin activity (PRA) elevation from cyclosporine (CsA) may also be major factor in the progress of hypertension. To investigate this hypothesis, observations of BP, creatinine (Cr), and PRA were made in 144 heart transplant recipients followed for up to four and a half years. Median Cr was 133 mumol/l. Average diastolic BP and mean PRA values were significantly higher in patients with Cr greater than or equal to the median. Cr and PRA were significantly correlated (r = 0.4; P less than 0.001) in recipients with Cr greater than or equal to 133 mumols/l but not in those with Cr less than 133 mumols/l. In a selected subsample of heart transplant recipients with repeated Cr and PRA values, Cr and PRA appeared to increase longitudinally after transplant. These data are derived from a case series of patients managed on a variety of antihypertensive agents (excluding ACE inhibitors) needed to control the persistent hypertension.

Relaxation therapy for hypertension. Comparison of effects with concomitant placebo, diuretic, and beta-blocker.

We compared the effects of relaxation therapy in hypertensive patients taking placebo, a beta-blocker (atenolol, 100 mg/d), or a diuretic (chlorthalidone, 50 mg/d), and we also compared the effects of relaxation therapy with the effects of the latter two drugs alone. Blood pressures were measured not only in the relaxation therapists' office and at a hypertension clinic, but also in the patient's environment by means of 24-hour ambulatory blood pressure recordings. The effect of relaxation therapy, while statistically significant, was modest. There was no generalization of effect to ambulatory blood pressure. Atenolol was significantly more effective than relaxation in reducing both systolic and diastolic pressure. Chlorthalidone was significantly more effective than relaxation in reducing systolic but not diastolic pressure in the hypertension clinic only. The long-term effects of relaxation were independent of concomitant drug use, but within the actual relaxation sessions blood pressure dropped further during chlorthalidone than during placebo or atenolol treatment.

The contrasting effects of cyclosporin-A and azathioprine on arterial blood pressure and renal function following cardiac transplantation.

The effects of cyclosporin-A and azathioprine on the postoperative development of systemic hypertension and renal dysfunction in patients undergoing cardiac transplantation were compared retrospectively in 18 patients receiving cyclosporin-A and in 12 patients receiving azathioprine. Twelve months postoperatively, the average mean blood pressure was 116 +/- 13 mm Hg and 98 +/- 7.5 mm Hg; the average preoperative serum creatinine was 1.2 +/- 0.3 mg% and 1.5 +/- 0.3 mg%; and the postoperative serum creatinine was 2.2 +/- 0.8 mg% and 1.1 +/- 0.2 mg% (P less than 0.0001) in the cyclosporin-A-and azathioprine-treated groups respectively. Hemodynamic studies were done to characterize the de novo postoperative hypertension developing in the cyclosporin-A group. The pre- and postoperative cardiac output was 3.7 and 4.91/min, respectively (P less than 0.01). The pre- and postoperative systemic vascular resistance was 1707 and 1941 dynes sec X cm-5, respectively (P greater than 0.2). Peripheral renin activity and 24-hour urinary catecholamine excretion were not elevated. The mechanism of the hypertension developing in cyclosporin-A-treated patients is unknown, but is associated with normalization of cardiac output, an abnormally elevated systemic vascular resistance, and modest impairment of renal function. These findings are in marked contrast to azathioprine-treated patients, in whom postoperative hypertension and renal dysfunction do not occur. These observations implicate cyclosporin-A as the major contributing factor in the development of hypertension and renal dysfunction.

Once-a-day triple therapy with low-dose minoxidil for moderate hypertension.

Minoxidil was given to 16 men with hypertension of various degrees of severity, in conjunction with a diuretic and atenolol. Mean supine and standing blood pressures (BP) on diuretic + atenolol were 172/106 and 162/104 mm Hg, respectively. Minoxidil was added and the dose titrated to lower the diastolic pressure to less than 90 mm Hg. All drugs were taken together once daily. At the end of a maintenance period of 6 months on an average dose of minoxidil of 12 mg (range 2.5 to 20.0 mg), supine BP was 147/87 and standing BP 139/88 mm Hg. Similar BP had been measured throughout the maintenance period, and monitoring of the BP showed that the once daily regimen provided good control for 24 h. A strong correlation was found between the dose of minoxidil necessary to normalize the BP and the mean arterial pressure prior to minoxidil (r = 0.73, P less than 0.005). Serious adverse effects of the drug were observed only in patients receiving doses greater than 10 mg or those with widespread atherosclerosis, or both. We conclude that, when added to a diuretic and a beta-blocker in a once-a-day regimen, minoxidil in a daily dose of less than or equal to 10 mg is effective and well tolerated in mild to moderate hypertension, especially in patients who are free of atherosclerotic complications.

Loss of nocturnal decline in blood pressure after cardiac transplantation.

Twenty-four hour noninvasive ambulatory blood pressure and heart rate monitoring was performed on patients who underwent orthotopic cardiac transplantation, as part of the investigation of the de novo hypertension that developes in such patients. Patients with essential hypertension served as control subjects. The results demonstrated a highly significant loss of the usual decline in blood pressure and heart rate during sleep in the transplant patients. A similar loss of nocturnal decline in blood pressure was noted in a group of 10 patients with autonomic neuropathy secondary to diabetes mellitus. The de novo hypertension associated with cardiac transplantation is probably multicausal. Impairment of renal function by cyclosporin-A with associated salt and water retention and persistent elevation of the systemic vascular resistance in the presence of a restored normal cardiac output by the "new" heart are major factors. In addition, loss of the normal nocturnal decline in blood pressure and heart rate, which probably is related to the denervated state of the transplanted heart, may play an important role in blood pressure control.

Central processing uncertainty as a determinant of choice reaction time.

It was demonstrated that central processing uncertainty (Hc) can be derived to provide a single valued statement of the information hypothesis RT=a+b (Hc) across test stimulus sets and across several levels of test stimulus probability in an information reduction task. The derivation procedure assumes successive tests of stimulus hypotheses with Bayesian revision of stimulus probabilities after failure of an initial test. It was shown that the procedure can be generalized to data from single test stimuli in an information conservation task. Stimulus and response repetition effects were estimated for the information reduction task data.

On the nature of central processing in choice reactions.

A procedure for generating values of central processing uncertainty was developed from positive response data in a varied-set version of the Sternberg choice reaction task. This is a logical extension of a previously validated procedure for data from a fixed-set version of the same task. Both procedures provide information on the additive components of reaction time. It was concluded that S resolves more uncertainty in the varied-set than in the fixed-set situation. It was concluded also that S performs a rechecking operation prior to emitting a negative response, and this rechecking apparently involves less information than does the original testing for stimulus classification. This, in turn, suggests that rechecking is a self-terminating process with regard to display information. The results also imply that stimulus classification is partially serial and partially parallel, so a hybrid model may be appropriate for this task.