A number of iterative image reconstruction algorithms were integrated into one formula characterizing each algorithm by only two parameters: overrelaxation and number of subsets. From the formula it follows that the o...
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A number of iterative image reconstruction algorithms were integrated into one formula characterizing each algorithm by only two parameters: overrelaxation and number of subsets. From the formula it follows that the ordered-subsets iteration (OS-EM) is equivalent to iteration with overrelaxation, where the OS level corresponds to the overrelaxation parameter. Algorithms represented by the formula were studied with respect to speed of convergence and image characteristics. In particular, OS-EM was compared with a single-projection iteration procedure using an optimized sequence of overrelaxation parameters (HOSP) which combines rapid convergence with reduced storage requirements. As a result, OS-FM with a constant number of subsets either needed more iteration steps than HOSP or provoked additional noise, depending on the number of subsets used during iteration. OS-FM can be improved by using decreasing OS levels, imitating the decreasing overrelaxation parameters used for HOSP. The resulting OS-FM may be slightly more rapid than HOSP, due to the increasing number of projections used simultaneously.
Background: The role of imaging studies before parathyroidectomy has been extensively debated and recent advances in unilateral parathyroidectomy intensify this controversy. The purpose of this study was to review the...
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Background: The role of imaging studies before parathyroidectomy has been extensively debated and recent advances in unilateral parathyroidectomy intensify this controversy. The purpose of this study was to review the parathyroidectomy experience of a single surgeon, looking at the role of sestamibi scans and a standard postoperative care regimen. Study Design: Retrospective review of office and hospital charts was completed on 90 patients with primary hyperparathyroidism who underwent parathyroidectomy from 1991 to 1998. Patient workup and outcomes were noted, as were results of preoperative imaging. True-positive scans visualized an abnormality ipsilateral to the adenoma found at operation. Statistics were performed using nonparametric testing and Student's t-test. Results: There were 21 male and 69 female patients, with an average age of 54 years (range 29 to 81). There were zero mortalities, three morbidities (3.3%), and three patients who had persistent hypercalcemia, yielding a 96.7% success rate. Sixty-seven patients underwent preoperative sestamibi scanning, with a sensitivity of 74% and positive predictive value of 89%. Operative rime in imaged patients averaged 103 +/- 49.9 minutes versus 121.5+/-85.9 minutes for patients without sestamibi scans. Operating time differences were not statistically significant and a preoperative sestamibi scan did not affect the success of parathyroidectomy. Discharge on postoperative day 1 was accomplished in 80% of patients and 13% were discharged the next day. There was no morbidity from hypocalcemia. Conclusions: A preoperative sestamibi scan does not improve efficacy or decrease operating time for primary hyperparathyroidism when bilateral neck exploration is performed. A postoperative care protocol including oral calcium and vitamin D supplementation allows the majority of patients to be discharged on postoperative day 1 with excellent results. (J Am Coil Surg 2000;190:540-545. (C) 2000 by the American College of Surgeo
Objectives Th. purpose of this study was to determine the effect of usual-dose estrogen replacement therapy (ERT) on myocardial perfusion and myocardial perfusion reserve (MPR) (evoked by an endothelium-independent va...
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Objectives Th. purpose of this study was to determine the effect of usual-dose estrogen replacement therapy (ERT) on myocardial perfusion and myocardial perfusion reserve (MPR) (evoked by an endothelium-independent vasodilator) in healthy postmenopausal women. Postmenopausal women have a decreased myocardial perfusion reserve compared with younger women. Estrogen infusions are known to enhance endothelium-dependent vasodilation of the epicardial coronary arteries in postmenopausal women, but whether ERT also enhances endothelium-independent myocardial perfusion and perfusion reserve is unclear. Methods In 2.4 healthy postmenopausal women who were not taking ERT, myocardial perfusion at rest, perfusion during the infusion of adenosine (a primarily endothelium-independent vasodilator), and MPR were determined by positron-emission tomography (PET) and oxygen 15-labeled water. The women were then randomly assigned in a double-blind fashion to receive either 0.625 mg of oral conjugated estrogens (Premarin) or placebo per day for 4 to 6 weeks, after which they underwent a repeat cardiac PET study. Results There was no statistical difference between those assigned to ERT and those assigned to placebo in the measurement of myocardial perfusion at rest (1.21 +/- 0.31 vs 1.16 +/- 0.18 mL/g/min, respectively) in response to adenosine (2.66 +/- 0.96 vs 3.3 +/- 0.45 mL/g/min) or MPR (2.24 +/- 0.83 vs 2.88 +/- 0.64 mL/g/min) after 4 to 6 weeks of oral ERT. There was also no difference between the groups in any of the myocardial perfusion measurements after correction for the rate-pressure product. Conclusions Short-term oral ERT does not affect myocardial perfusion at rest in response to adenosine or MPR in healthy postmenopausal women. Thus potential beneficial effects of ERT on vasomotor function may be limited to enhancement of endothelium-dependent vasodilative mechanisms affecting conduit vessels.
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