Pregnant women's perspectives on integrating preventive oral health in prenatal care.

BACKGROUND: Oral diseases are considered a silent epidemic including among pregnant women. Given the prevalence of oral conditions among pregnant women and the reported association with adverse pregnancy outcomes, there have been suggestions for the inclusion of preventive oral care in routine prenatal care. However, due to the different administrative and funding structure for oral health and prenatal care in Canada, progress towards this integration has been slow. Our study sought to qualitatively explore the views of pregnant women in British Columbia (BC) on the strategies for integrating preventive oral health care into prenatal care services. METHODS: A qualitative approach was utilized involving semi-structured interviews with fourteen (14) purposefully selected pregnant women in Vancouver and Surrey, BC. The interviews were audio-recorded and transcribed. The transcripts were analyzed using an inductive thematic approach. Study validity was ensured via memoing, field-notes, and member checking. RESULTS: Interviews ranged from 28 to 65 min producing over 140 pages of transcripts. Analysis resulted in three major themes: oral health experiences during pregnancy, perspectives on integration and integrated prenatal oral care, and strategies for addressing prenatal oral health care. A majority of participants were supportive of integrating preventive oral care in routine prenatal services, with referrals identified as a critical strategy. Oral health education was recognized as important before, during, and after pregnancy; oral health assessments should therefore be included in the prenatal care checklist. Limited funding was acknowledged as a barrier to oral health care access, which may explain why few participants visited their dentists during pregnancy. Interprofessional education surfaced as a bridge to provide prenatal oral health education. CONCLUSION: Pregnant women interviewed in this study support the inclusion of educational and preventive oral care during prenatal care, although their views differed on how such inclusion can be achieved in BC. They advocated the establishment of a referral system as an acceptable strategy for providing integrated prenatal oral health care.

High average power Q-switched 1314-nm two-crystal Nd:YLF laser.

A 1314 nm two-crystal Nd:YLF laser was designed and operated in both CW and actively Q-switched modes. Maximum CW output of 26.5 W resulted from 125 W of combined incident pump power. Active Q-switching was obtained by inserting a Brewster-cut acousto optic modulator. This setup delivered an average power of 18.6 W, with a maximum of 5.6 mJ energy per pulse with a pulse duration of 36 ns at a pulse repetition frequency of 500 Hz.

High average power 1314 nm Nd:YLF laser, passively Q-switched with V:YAG.

A 1314 nm Nd:YLF laser was designed and operated both CW and passively Q-switched. Maximum CW output of 10.4 W resulted from 45.2 W of incident pump power. Passive Q-switching was obtained by inserting a V:YAG saturable absorber in the cavity. The oscillator delivered a maximum of 825 µJ energy per pulse, with a pulse duration of 135 ns at a pulse repetition frequency of 6.3 kHz, effectively delivering 5.2 W of average power.

Dental Service and Resource Needs during COVID-19 among Underserved Populations.

INTRODUCTION: In response to the coronavirus disease 2019 (COVID-19) outbreak, dental services in British Columbia, Canada, were restricted to urgent and emergency cases between March 16 and May 18, 2020. It is unclear how the curtailment of oral health services has affected underserved populations who already often have limited access to dental care due to cost, fear, stigma, and discrimination. OBJECTIVES: To explore the experiences of underserved populations and their community organizations when accessing oral health services and information in British Columbia and identify their coping mechanisms employed during the curtailment of oral health care services. METHODS: Semistructured, remote interviews were conducted with 13 staff and 18 members from 6 community-based organizations. These organizations serve men and women with a history of incarceration and/or experiencing poverty and homelessness, persons living with human immunodeficiency virus/AIDS, adults living with mental illness, and older adults in long-term care facilities. The interviews were audio-recorded, transcribed verbatim, and coded for emerging themes using NVivo 12 software. Thematic analysis was performed. RESULTS: The pandemic raised concerns and hesitancy among underserved populations and further reduced access to care. In turn, those with unmet dental needs resorted to coping mechanisms, including turning to community support or medical services, self-management of dental issues, and not dealing with dental issues altogether. Community organizers and members outlined needed resources such as assistance navigating the dental care system, having a contact for dental-related questions, and member preparation for dental service changes, while emphasizing the importance of positive relationships with dental providers. CONCLUSION: Underserved populations who already face barriers to oral health care services experienced increased difficulty in addressing their oral health needs and concerns during the beginning of the COVID-19 pandemic. Strategies aimed at reaching out to this population and those who support them are needed to help mitigate negative coping strategies and increased oral health disparities. KNOWLEDGE TRANSFER STATEMENT: This study depicts ways of addressing unmet oral health-related issues during the COVID-19 pandemic for underserved populations and their community organizations with policy implications as well as practical strategies.

Validation for 2D/3D registration. I: A new gold standard data set.

PURPOSE: In this article, the authors propose a new gold standard data set for the validation of two-dimensional/three-dimensional (2D/3D) and 3D/3D image registration algorithms. METHODS: A gold standard data set was produced using a fresh cadaver pig head with attached fiducial markers. The authors used several imaging modalities common in diagnostic imaging or radiotherapy, which include 64-slice computed tomography (CT), magnetic resonance imaging using T1, T2, and proton density sequences, and cone beam CT imaging data. Radiographic data were acquired using kilovoltage and megavoltage imaging techniques. The image information reflects both anatomy and reliable fiducial marker information and improves over existing data sets by the level of anatomical detail, image data quality, and soft-tissue content. The markers on the 3D and 2D image data were segmented using ANALYZE 10.0 (AnalyzeDirect, Inc., Kansas City, KN) and an in-house software. RESULTS: The projection distance errors and the expected target registration errors over all the image data sets were found to be less than 2.71 and 1.88 mm, respectively. CONCLUSIONS: The gold standard data set, obtained with state-of-the-art imaging technology, has the potential to improve the validation of 2D/3D and 3D/3D registration algorithms for image guided therapy.

Gastric emptying of glucose solution and associated plasma concentrations of GLP-1, GIP, and PYY before and after fundoplication.

BACKGROUND: This study was designed to assess the relationship between gastric emptying of glucose solution and the ensuing plasma concentrations of glucagon-like peptide-1 (GLP-1), peptide YY (PYY), and glucose-dependent insulinotropic polypeptide (GIP) in patients having undergone fundoplication for gastroesophageal reflux (GERD). SUBJECTS AND METHODS: In 10 male patients the emptying of 50% glucose solution was determined scintigraphically and its relationship with plasma glucose, GLP-1, PYY, and GIP concentrations was studied before and 3 months after fundoplication. RESULTS: In the first 30 min after glucose ingestion, emptying was significantly (p = 0.048) faster after fundoplication than before. Emptying and GLP-1 and GIP correlated: the faster the emptying during the first 30 min the greater the concentrations integrated over that period (p = 0.04; p = 0.01; p = 0.02). Emptying and PYY concentrations were unrelated. In the 120-180 min. period, blood glucose concentrations were lower the faster the emptying in the initial 30 min (p = 0.06) and the entire 50-min recording period (p = 0.03) had been. The GLP-1 concentrations integrated over the first 30 min correlated inversely with the integrated plasma glucose during the third hour after ingestion (p = 0.004). CONCLUSIONS: After fundoplication, gastric emptying may, if accelerated in its initial phases, give rise to greater and earlier increases in plasma glucose, GLP-1, and GIP concentrations and thus to reactive hypoglycemia.

Evaluation of a new electromagnetic tracking system using a standardized assessment protocol.

This note uses a published protocol to evaluate a newly released 6 degrees of freedom electromagnetic tracking system (Aurora, Northern Digital Inc.). A practice for performance monitoring over time is also proposed. The protocol uses a machined base plate to measure relative error in position and orientation as well as the influence of metallic objects in the operating volume. Positional jitter (E(RMS)) was found to be 0.17 mm +/- 0.19 mm. A relative positional error of 0.25 mm +/- 0.22 mm at 50 mm offsets and 0.97 mm +/- 1.01 mm at 300 mm offsets was found. The mean of the relative rotation error was found to be 0.20 degrees +/- 0.14 degrees with respect to the axial and 0.91 degrees +/- 0.68 degrees for the longitudinal rotation. The most significant distortion caused by metallic objects is caused by 400-series stainless steel. A 9.4 mm maximum error occurred when the rod was closest to the emitter, 10 mm away. The improvement compared to older generations of the Aurora with respect to accuracy is substantial.

Globus sensation: pharyngoesophageal function, psychometric and psychiatric findings, and follow-up in 88 patients.

BACKGROUND: The globus sensation has been widely regarded as psychogenic, but organic disorders were found to be etiologically significant. OBJECTIVE: To investigate the structural, functional, psychological, and psychiatric factors possibly eliciting the globus sensation and influencing its course. METHODS: Eighty-eight patients, 67 women and 21 men (aged 22-71 years), referred to 2 tertiary care centers underwent history taking, otolaryngological examination, pharyngoesophageal videofluoroscopy and manometry, psychosocial evaluation, psychometric tests, psychiatric interview, and when indicated, esophagogastroduodenoscopy, esophageal bolus transport, gastroesophageal reflux, and gastric emptying studies. According to revealed disorders, therapy was initiated, and the outcome was studied. RESULTS: Only 15 patients had normal pharyngoesophageal function; of these 15, 6 had chronic tonsillitis or pharyngitis, 3 had thyroid adenomata, 4 had cervical spondylosis, and 1 each had dry oropharyngeal mucosa and chronic bronchitis. Of the other 73 patients, 2 had pharyngeal dysfunction, 24 had achalasia, 1 had diffuse esophageal spasms, 3 had "nutcracker esophagus," 30 had nonspecific esophageal motor disorders, and 13 had gastroesophageal reflux. Psychometry revealed no more anxiety and depression than in general medical outpatients. Of 58 patients interviewed, 37 met criteria for psychiatric disorders. Psychometric scores and psychiatric characteristics were unrelated to the sensation's course. Therapy was recommended, but only 26 patients were treated accordingly; 22 received nonspecific treatment. Follow-up 3 to 59 months later revealed that the sensation had vanished in 13 patients who had received specific treatment, 5 who had received nonspecific treatment, and 6 who had received no treatment; it was alleviated in 10 who had received specific treatment, 13 who had received nonspecific treatment, and 9 who had received no treatment; and it was unchanged in 3 who had received specific treatment, 5 who had received nonspecific treatment, and 23 patients who had received no treatment. CONCLUSIONS: Pharyngoesophageal disorders may be sensed only vaguely, inducing the globus sensation. Psychological and psychiatric characteristics could be relevant to the discomfort experienced but are unlikely to be etiologically significant.

Slow gastric emptying in type I diabetes: relation to autonomic and peripheral neuropathy, blood glucose, and glycemic control.

OBJECTIVE: To investigate whether autonomic neuropathy or hyperglycemia plays a crucial etiological role in gastric retention of ingesta frequently found in type I diabetic patients. RESEARCH DESIGN AND METHODS: We investigated the gastric emptying of a radiolabeled semisolid 1,168 kJ meal in 38 female and 45 male patients (age 18-75 years; illness duration 3-46 years). None took drugs affecting gastrointestinal motility. Fasted patients underwent tests of cardiovascular autonomic and peripheral nerve function. Blood glucose levels were determined before and after the scintigraphic recording of gastric emptying. RESULTS: The percentage of meal remaining in the stomach at the end of the 50-min recording time was related significantly to the patients' degree of cardiovascular autonomic neuropathy [r (81) = 0.235, P < 0.028] but not to their degree of peripheral neuropathy, preprandial blood glucose level, HbA1c indicative of glycemic control, diabetes duration, and age. The patients' mean residual percentage of meal was significantly greater than that of 48 healthy subjects, that is, 71.1 +/- 15.1 vs. 53.5 +/- 13.1% [means +/- SD; t (129) = 6.48, P < 0.0001]. The healthy individuals' mean residual percentage + 2 SD was exceeded in 22 patients. CONCLUSIONS: Slow gastric emptying in patients with type I diabetes seems related to the degree of autonomic neuropathy but not to peripheral neuropathy, actual blood glucose, and glycemic control.

Cisapride versus placebo for 8 weeks on glycemic control and gastric emptying in insulin-dependent diabetes: a double blind cross-over trial.

In insulin-dependent diabetes mellitus, slow gastric emptying may make absorption unpredictable and foster glycemic instability. Cisapride accelerates emptying, but controlled long term studies are scarce, and effects on glycemic control unknown. We investigated, in patients with insulin-dependent diabetes mellitus and unstable glycemia, the effects of 10 mg cisapride 4 times daily for 8 weeks vs. placebo on glycemic control and gastric emptying under random, cross-over, double blind conditions. In 14 patients with delayed and 9 with nondelayed emptying, blood glucose variability over 28-week treatment periods separated by a 4-week wash-out and gastric emptying of a semisolid 1168-kJ meal immediately after the treatment periods were assessed. Cisapride did not affect glycemic control [SD of within-patient mean blood glucose, 4.2 mmol/L +/-0.1 (+/- SEM) vs. 4.0+/-0.1 mmol/L after placebo; hemoglobin A1c, 8.3+/-0.2% vs. 8.5+/-0.2%]. Emptying was faster after cisapride than after placebo in 8 of 14 patients with delayed vs. 7 of 9 with nondelayed emptying (P = NS) and in 11 of 15 without vs. 4 of 8 with cardiovascular autonomic neuropathy (P = NS). Autonomic neuropathy prevailed in 7 of 14 patients with delayed and 1 of 9 with nondelayed emptying. Blood glucose immediately before and during assessment of emptying was unrelated to the emptying rate, whereas blood glucose increases over fasting levels were greater with faster emptying (P<0.002). In conclusion, cisapride's effects were not different from those of placebo on glycemic control and gastric emptying, it did not differently affect patients with delayed vs. nondelayed emptying, and it slightly accelerated emptying (P = NS) in patients without, but not in those with, cardiovascular autonomic neuropathy. Blood glucose levels before and during assessment of emptying did not affect emptying, but the glucose rise over fasting levels was greater with faster emptying.

Influence of cilazapril on blood rheology in healthy subjects. A pilot study.

This study attempted to determine whether the autohemodilution that has repeatedly been shown to be induced by nitrates and other vasodilators is also produced by cilazapril. Fifteen healthy male volunteers were given 2.5 mg oral cilazapril daily for two weeks. Blood rheology was quantified by measuring blood and plasma viscosity, hematocrit count, red blood cell aggregation and deformability, and white blood cell clogging at baseline, four hours after first dose and four and 24 hours after the last dose. No acute or chronic changes were observed except for a significant increase in red blood cell deformability and a decrease in white blood cell clogging. It is concluded that hemodilution secondary to vasodilation may occur but be offset by hemoconcentration induced by aldosterone inhibition and decrease of anti-diuretic hormone levels. The changes in deformability and clogging may benefit microcirculatory function, a hypothesis that would need further investigation in controlled trials.

Angulation errors in parallel-hole and fanbeam collimators: computer controlled quality control and acceptance testing procedure.

UNLABELLED: Angulation errors in collimators of 1 degrees or even less can seriously diminish the resolution of SPECT images. We have developed a computer-controlled quality control procedure that can be used for acceptance testing and regular routine checks. METHODS: Using a marker point source and a computer-controlled x-y positioning table, we investigated 7 parallel-hole and 3 fanbeam collimators. The results are presented as collimator surface maps, which are easy to interpret visually. RESULTS: The measurement accuracy for absolute angulation errors was better than 0.32 degrees. Regional variations in channel tilt could be detected with an accuracy better than 0.16 degrees. Six parallel-hole collimators were found acceptable for high-resolution SPECT imaging. For a parallel-hole collimator that had to be replaced because of nonoptimal image quality, our measurements clearly identified regions of directionally uniform angulation errors. Two fanbeam collimators showed slight concavities. CONCLUSION: Automation of the measurement and evaluation process make this procedure suitable for both acceptance tests and routine quality control checks. It can be applied to parallel-hole, fanbeam, converging, and diverging collimators, regardless of their individual geometry. No technical collimator specifications are needed. Our results reveal subtle mechanical deformations of collimators. They also show that for a detailed investigation, angulation error surface maps should be used to discover regional preferences in channel orientation.

Gastric emptying of semisolid meal unaltered by 3 days' administration of a sustained-release preparation of the nitric oxide donor, isosorbide dinitrate.

BACKGROUND: Evidence has accumulated that nitric oxide is involved in the regulation of gastrointestinal motor activity. We investigated whether nitric oxide derived from a sustained-release isosorbide dinitrate (Cedocard retard) had an effect on gastric emptying and on subjective feelings. METHODS: Twelve healthy males aged 23-32 years received at weekly intervals, for 3 days twice daily, either 20 mg isosorbide dinitrate, 40 mg isosorbide dinitrate, or placebo, under random double-blind conditions. After a further dose on day 4, subjects ate a 1168 kJ semisolid meal, the emptying of which was recorded scintigraphically for 50 min. RESULTS: Neither dosage of isosorbide dinitrate had an effect on emptying which differed from the effect of placebo and the effects of the two dosages were the same. The radioactivity remaining in the stomach 50 min postprandially was 68.5% +/- 4.5 S.E.M. after placebo, 65.4 +/- 5.6% after 20 mg isosorbide dinitrate and 66.1 +/- 4.4% after 40 mg isosorbide dinitrate. With 40 mg isosorbide dinitrate, all 12 subjects complained of persistent headache, whereas only slight headache was reported by 7 subjects on 20 mg isosorbide dinitrate and by 1 subject on placebo. CONCLUSION: Twenty and 40 mg doses of sustained-release isosorbide dinitrate twice daily had no effect on the gastric emptying of a semisolid meal, but dose-dependently induced headaches.

Enantioselective photochemical reactions of 2-pyridones in solution.

[reaction: see text] Two key photochemical reactions of prochiral 2-pyridones were studied in the presence of a chiral host. The [4 + 4]-photocycloaddition with cyclopentadiene (CpH) proceeded smoothly and with high enantioselectivity (84-87% ee). The absolute configuration of the endo-diastereoisomer was established by X-ray crystallography. The electrocyclic [4pi]-ring closure to 3-oxo-2-azabicyclo[2.2.0]-5-hexenes occurred with lower enantioselectivity (20-23% ee at -20 degrees C). The velocity of the latter reaction slowed significantly with decreasing temperature.

Achalasia. Results of myotomy and antireflux operation after failed dilatations.

OBJECTIVE: To evaluate the outcomes of patients with achalasia who had undergone myotomy and an antireflux operation because dilatations had not yielded satisfactory results. DESIGN: Retrospective analysis. SETTING: University-based tertiary care center. PATIENTS: Of 39 patients who met inclusion criteria, 18 female patients and 18 male patients (age range; 17-85 years; median age, 54 years; range of time elapsed since operation, 1-22 years; median time, 6 years) could be studied. Antireflux operations included 360 degrees fundoplications in 27 patients, anterior hemifundoplications in 5 and other procedures in 4. MAIN OUTCOME MEASURES: Dysphagia for solid foods and liquids, regurgitation, heartburn, retrosternal pain and body weight. RESULTS: Excellent, good, and fair results of myotomy and antireflux operation were encountered in 14, 3, and 6 patients, respectively, and poor or absent results in the remaining 13 patients. The resting pressure of the lower esophageal sphincter was significantly lower at follow-up than preoperatively, and this was associated with reduced dysphagia for solid foods in 14 patients and for liquids in 16 of 17 patients. CONCLUSIONS: Myotomy and antireflux operation yielded excellent to fair results in 23 patients in whom dilatations had not facilitated swallowing. Poor results in the remaining 13 patients seemed to be attributable to the 360 degrees fundoplication performed in 12 of them. In these patients, a further surgical intervention seemed to be indicated.

Prostacyclin I2 (PGI2) increases left ventricular ejection fraction (LVEF).

In order to evaluate the effect of PGI2 on left ventricular ejection fraction (LVEF) an intravenous infusion in 10 patients (3 males, 7 females; 36 to 63 years) with an impaired LVEF (34.7 +/- 14.8%) was performed. LVEF was determined by means of 99mTc-pertechnetate radionuclide ventriculography. An increase of LVEF to 36.2 +/- 13.5% during administration of PGI2 at a rate of 1 ng/kg/min for 15 min and to 43.8 +/- 15.8% during a rate of 5 ng/kg/min (p less than 0.01) for an additional 15 min was observed. Analyzing the data in more detail in 6 patients, an improvement in LVEF became obvious during the administration of 1 ng/kg/min (108, 109, 116, 118, 121, and 123% of pre-infusion value, respectively). In 5 out of these 6 patients a dose-increment to 5 ng/kg/min further increased LVEF (139, 179, 187, 148, and 128% of pre-infusion value, respectively). In contrast, in the other 4 patients no response of LVEF to PGI2 at a rate of 1 ng/kg/min could be observed. However, in 2 out of these 4 patients LVEF increased during the administration of 5 ng/kg/min (111 and 117% of pre-infusion value). Individual changes in hemodynamic parameters showed no correlation to the improvement seen in LVEF in response to PGI2. It is concluded that PGI2 may exert beneficial effects on LVEF, and might be used in certain clinical conditions, such as before heart transplantation, to achieve a temporary improvement in LVEF.

Beating heart operations including hybrid revascularization: initial experiences.

BACKGROUND: The outcome of patients (n = 45) with coronary one- to three-vessel disease undergoing beating heart operations using a recently developed stabilizing device was investigated. METHODS: Left internal mammary artery-to-left anterior descending coronary artery (LIMA-to-LAD) revascularization was carried out alone (n = 31) or as hybrid procedure in combination with a balloon angioplasty (n = 14). RESULTS: All 45 patients underwent a successful LIMA-to-LAD procedure without intraoperative complication during a 21 +/- 8-minute (range, 10 to 53 minutes) LAD occlusion time. In 14 hybrid procedures a total of 19 stenoses including 3 left main stenoses were treated successfully by percutaneous transluminal coronary angioplasty and stenting. The postoperative courses were uneventful with the exception of two surgical reexplorations necessitated by bleeding. No worsening of renal, neurologic, or respiratory functions occurred in any patient. In the group having a single LIMA-to-LAD procedure, early postoperative coronary angiograms (22 of 31) showed a patent LIMA graft and excellent anastomosis; this was also true in 4 patients 12 months after operation as shown in angiograms. All patients undergoing hybrid revascularization demonstrated a patent LIMA-to-LAD anastomosis; in 1 patient there was a dissection in the midlevel of the LIMA, which was stented successfully. The 6-month follow-up angiograms in 7 of 14 patients revealed open LIMA bypass grafts in all patients except 1, who was stented because of dissection. CONCLUSIONS: These data indicate that a beating heart operation including hybrid revascularization is safe and effective in selected patients with coronary one- to three-vessel disease including left main stenosis. This approach may be especially advantageous in comparison with conventional coronary artery bypass grafting in patients with severe concomitant disease.

Substitution of antithrombin III in shock and DIC: a randomized study.

In 51 shock patients with DIC Antithrombin III (AT III) substitution, heparin or a combination of both substances respectively was administered. In the two groups which had been given AT III substitution the concentration of AT III rose considerably higher than the activity. There was a drop of the platelet count in both groups which had received heparin. C1 esterase inhibitor was diminished in the beginning but spontaneously increased in all groups. This increase was slowest in the group without substitution of AT III. The blood loss in cases of traumatic shock was considerably higher in the group which had received both substances. The consumption of AT III concentrates was slightly higher in the combined therapy group than in the AT III group. The duration of symptoms of DIC was considerably shorter in the two substituted groups than in the heparin group. It is concluded that additional administration of heparin does not improve the effect of AT III substitution in patients with DIC and that side effects such as thrombocytopenia and an increased blood loss are likely to develop when both substances are given simultaneously.

Substitution therapy with an antithrombin III concentrate in shock and DIC.

In 15 patients admitted to the Intensive Care Unit for shock and with signs of DIC, Antithrombin III (AT III) was substituted. Immediately after the first blood sampling, 1,000 units of AT III was given. This was followed by 500 units AT III after 24 h and after 48 h. A continuous dose of heparin of between 250 and 500 I.U./h was simultaneously given. The following results were obtained: The activity of AT III on admission of 63 +/- 19% increased to 83 +/- 17% 30 min after the initial substitution. There was a clear difference between the recovery of the substituted AT III in acute DIC and in patients in a steady state. AT III recovered in circulation was 47 +/- 15% in the former group but 83 +/- 16% in the latter cases. One unit of AT III per kg body weight increased AT III activity in circulation by 1% in acute DIC but by 1.8% in a steady state. The average half life of the substituted AT III was 4.4 +/- 1.6 h in acute DIC and was 20.2 +/- 4.1 h when the patients were in a steady state.

Systematic distortions in magnetic position digitizers.

Medical devices equipped with position sensors enable applications like image guided surgical interventions, reconstruction of three-dimensional 3D ultrasound (US) images, and virtual or augmented reality systems. The acquisition of three-dimensional position data in real time is one of the key technologies in this field. The systematic distortions induced by various metals, surgical tools, and US scan probes in different commercial electromagnetic tracking systems were assessed in the presented work. A precise nonmetallic six degree-of-freedom measurement rack was built that allowed a quantitative comparison of different electromagnetic trackers. Also, their performance in the presence of large metallic structures was quantified in a phantom study on an acrylic skull model in an operating room (OR). The trackers used were alternating current (ac) and direct current (dc) based systems. The ac trackers were, on average, distorted by 0.7 mm and 0.5 degree by metallic objects positioned at a distance greater than 120 mm between the geometrical center of the sample and the sensor. In the OR environment, the ac system exhibits mean errors of 3.2 +/- 2.4 mm and 2.9 degrees +/- 1.9 degrees. The dc trackers are more sensitive to distortions caused by ferromagnetic materials (averaged value: 1.6 mm and 0.5 degree beyond a distance of 120 mm). The dc tracker shows no distortions from other conductive materials but was less accurate in the OR environment (typical error: 6.4 +/- 2.5 mm and 4.9 degrees +/- 2.0 degrees). At distances smaller than approximately 100 mm between sample and sensor error increases quickly. It is also apparent from our measurements that the influence of US scan probes is governed by their shielding material. The results show that surgical instruments not containing conductive material are to be preferred when using an ac tracker. Nonferromagnetic instruments should be used with dc trackers. Static distortions caused by the OR environment have to be compensated by precise calibration methods.