Noise performance of a precision pulsed electromagnet power supply for magnetic resonance imaging.

Prepolarized magnetic resonance imaging (PMRI) uses two pulsed electromagnets to achieve high-field image quality with the benefits of low-field data acquisition. The principal challenge with all resistive MRI systems is the implementation of a highly precise magnet current supply. The noise current through the magnet is fundamentally limited by the current transducer used to provide feedback and the voltage reference used to generate the demand signal. Field instability in the main field magnet can both corrupt the received data and degrade the robustness of Carr¿Purcell¿Meiboom¿Gill (CPMG) echo trains, which are paramount to efficient imaging in PMRI. In this work, we present the magnet control system that achieved sufficient field stability for PMRI at $0.5/0.13$ T, identify the dominant sources of noise in the control system, examine the imaging artifacts that can occur if the field stability is insufficient, and identify how the design can be improved for better field stability, should it be required for future implementations of PMRI.

Real-time black-blood MRI using spatial presaturation.

A real-time interactive black-blood imaging system is described. Rapid blood suppression is achieved by exciting and dephasing slabs outside the imaging slice before each imaging excitation. Sharp-profiled radio frequency saturation pulses placed close to the imaging slice provide good blood suppression, even in views containing slow through-plane flow. In vivo results indicate that this technique improves endocardial border definition during systole in real-time cardiac wall-motion studies. Phantom and animal results indicate that this technique nearly eliminates flow artifacts in real-time intravascular studies. J. Magn. Reson. Imaging 2001;13:807-812.

What is the next step in patient decision support?

Patient decision support systems have a promising role in the delivery of health care. However, the best approach for further development of these systems is a matter of speculation. To help chart a course for further development of decision support systems, we consider the four traditional roles that patients play in the medical decision making process, the limitations that patients face in participating in each role and describe how contemporary systems address can facilitate successful decision making for each role. Because patients have a diversity of preferences for the role they play in decision making, we believe that the critical research question is how to make decision support systems robust enough to support a patient's desired role, whatever that role might be. By directing research in decision support systems in this fashion, we believe that they will achieve a larger patient audience and have increased value in the delivery of clinical care.

Extending contemporary decision support system designs to patient-oriented systems.

Decision support systems for patients can benefit from adopting knowledge engineering-based architectures. In this paper, we describe how decision support systems for patients differ from decision support systems for health professionals and knowledge engineering principles that can be used to improve the efficiency of developing patient support systems. We discuss a five-step process model for patient-computer dialogue and its incorporation into an architecture based on knowledge engineering ontologies. The architecture's components are grouped into transient and persistent application layers that support a general framework for patient decision support. The implementation of the object-based model using a relational database management system is also discussed.

CT patterns of nodular hepatic and splenic sarcoidosis: a review of the literature.

PURPOSE: The purpose of our study was to investigate the less commonly demonstrated CT patterns nodular hepatosplenic sarcoidosis. METHOD: We studied five women patients, utilizing contrast enhanced incremental or spiral CT. We also performed a literature search of hepatosplenic sarcoid for the years 1966-1995. RESULTS: We found five nodular hepatic and/or splenic patterns of sarcoidosis. CONCLUSION: We conclude that increased awareness and recognition of these patterns of nodular hepatic/splenic sarcoidosis on CT will greatly improve detection and diagnosis of abdominal sarcoidosis.

SecondOpinion: interactive Web-based access to a decision model.

In this paper, we describe a computer architecture, which we call SecondOpinion, designed for automated, normative patient decision support over the World Wide Web. SecondOpinion custom tailors the discussion of therapy options for patients by eliciting their preferences for relevant health states via an interactive WWW interface and then integrating those results in a decision model. The SecondOpinion architecture uses a Finite State Machine representation to track the course of a patient's consultation and to choose the next action to take. The consultation has five distinct types of interactions: explanation of health states, assessment of preferences, detection and correction of errors in preference elicitations, and feedback on the implications of preference. A linear "summary model" speeds calculations of predictions from the decision model and makes it possible to dynamically calculate 95% confidence intervals for the marginal utility of each treatment option. Preferences for states are assessed in the order of their variance contribution to the models predictions in an iterative fashion. Only the states required to obtain a 95% Confidence Interval (CI) that excludes zero are assessed. In Monte Carlo simulation studies, the average number of utility assessments required for the 95% CI to exclude zero in an individual was 4.24 (SD = 1.97) out of 8 relevant health states. the SecondOpinion architecture provides an efficient, "discussion-like" experience leading to an individual-specific treatment recommendation. It may be a cost-effective approach to bring decision analytic advice to the bedside.

Cervical lymph node metastasis of thyroid papillary carcinoma imaged with fluorine-18-FDG, technetium-99m-pertechnetate and iodine-131-sodium iodide.

A 49-yr-old white woman with diffuse sclerosing variant of papillary carcinoma of the thyroid revealed abnormal [18F]FDG accumulation within cervical lymph node metastases prior to thyroidectomy. The abnormal cervical foci of glucose metabolism corresponded to similar areas of abnormal [99mTc]pertechnetate and radioiodine accumulation on presurgical scans. The primary thyroid tumor within the thyroid gland was not delineated as a focal defect on any of the three imaging studies. The relative thyroid-to-background soft-tissue ratio in the [18F]FDG study, however, appeared higher than usual. As with 131I and [99mTc]pertechnetate, this case demonstrates that [18F]FDG PET can detect cervical lymph node metastases in the preoperative thyroid cancer patient.

Indium-111 OncoScint CR/OV and F-18 FDG in colorectal and ovarian carcinoma recurrences. Early observations.

Indium-111 satumomab pendetide (In-111 OncoScint) planar and SPECT imaging and F-18 FDG positron emission tomography (PET) have been found individually to be helpful in the detection of recurrent colorectal and ovarian cancer, but have not been compared. Twelve patients who were examined for recurrent colorectal or ovarian carcinoma underwent both In-111 OncoScint imaging and F-18 FDG PET imaging. All had normal or equivocal results of CT or MR studies. Tumor detection abilities were similar in most cases. However, Oncoscint demonstrated an advantage in the detection of carcinomatosis. PET demonstrated an advantage in detecting focal tumor recurrence in one case and, not unexpectedly, in detecting liver metastases. All positive nuclear studies for tumor were found to be true-positives at pathology (7 patients), or by diagnostic new CT changes (1 patient). Finally, unreported, bone marrow, bowel, and colostomy sites appear to be normal sites of localization of F-18 FDG 1 hour after injection.

Rotating frame RF current density imaging.

RF current density imaging (RF-CDI) is a new MRI technique for imaging the Larmor frequency current density parallel to B0 in electrolytic media. To extend the use of RF-CDI to biological tissue for generating conductivity contrast, the sensitivity must be increased and the data requirements reduced. A rotating frame approach, in which a large B1 field is applied simultaneously as a rotary echo with RF current, is proposed to meet these requirements. Rotating frame magnetic fields are encoded in the phase of an MRI image. Trials have now been performed with this sequence in a three-compartment cylindrical phantom containing doped water or mineral oil for detecting displacement, conduction and fringe field currents. In a postmortem rat study, 85.56 MHz RF currents injected by implanted electrodes created tissue dependent contrast because of the electrical properties of tissue. A sensitivity and artifact analysis was also performed. The sensitivity of this method is determined by the maximum RF pulse duration. SAR limits pose an upper bound on this time and B1, whereas the avoidance of phase artifacts imposes a lower bound on B1.

Electromagnetic considerations for RF current density imaging [MRI technique].

Radio frequency current density imaging (RF-CDI) is a recent MRI technique that can image a Larmor frequency current density component parallel to B(0). Because the feasibility of the technique was demonstrated only for homogeneous media, the authors' goal here is to clarify the electromagnetic assumptions and field theory to allow imaging RF currents in heterogeneous media. The complete RF field and current density imaging problem is posed. General solutions are given for measuring lab frame magnetic fields from the rotating frame magnetic field measurements. For the general case of elliptically polarized fields, in which current and magnetic field components are not in phase, one can obtain a modified single rotation approximation. Sufficient information exists to image the amplitude and phase of the RF current density parallel to B(0) if the partial derivative in the B(0) direction of the RF magnetic field (amplitude and phase) parallel to B(0) is much smaller than the corresponding current density component. The heterogeneous extension was verified by imaging conduction and displacement currents in a phantom containing saline and pure water compartments. Finally, the issues required to image eddy currents are presented. Eddy currents within a sample will distort both the transmitter coil reference system, and create measurable rotating frame magnetic fields. However, a three-dimensional electro-magnetic analysis will be required to determine how the reference system distortion affects computed eddy current images.

Use of a face mask in the measurement of resting ventilatory parameters and mouth occlusion pressures.

A recent study has suggested that mouth occlusion pressure (MOP) could be measured during sleep by using a face mask. The purpose of the present study was to examine the effects of a face mask on MOP and resting ventilatory parameters (RVP). Measurements of MOP and RVP were made by three different methods; while breathing through a mouthpiece with nose-clip (MP+NC), through a face mask breathing through the mouth only (FM/mouth), and through a face mask breathing through the nose only (FM/nose). There was a significant difference in several RVP parameters between MP+NC and FM, but no significant difference in MOP between different methods. Use of FM for the measurement of MOP appears to be warranted, and with regard to RVP consideration needs to be given to the differences found between MP+NC and FM.

The effects of transtracheal gas delivery on central inspiratory neuromuscular drive.

Previous studies have shown transtracheal delivery of low-flow oxygen (TTO) decreases inspired minute ventilation (Veinsp) and have postulated that this would result in a decrease in the work of breathing (WOB). We hypothesized that a fall in central inspiratory neuromuscular drive (CIND) with TTO would reflect a fall in WOB. We measured resting ventilatory parameters (RVP) and CIND by the mouth occlusion pressure technique (MOP) at different gas flow rates through the catheter in 21 subjects (13 men, 8 women; mean age, 60 +/- 10.6 years) with severe COPD with a mature intratracheal oxygen catheter (ITOC). We also constructed a lung/chest wall analog (LCA) to determine if flow through the catheter would alter pressure changes during inspiration. Inspiratory tidal volume (Vtinsp) and minute ventilation (Veinsp) decreased proportionally to the gas flow rate through the catheter. However, with increasing flow through the catheter, P0.1 increased in the LCA, presumably due to the Bernoulli effect. The lack of a similar change in the subject group suggests that CIND does, in fact, fall, and that possibly there is a decrease in WOB. This effect may be of benefit to patients with severe COPD.

Dobutamine, but not dopamine, augments the normal chronotropic response to acute hypoxemia.

Infusion of exogenous dopamine has been shown to alter both the hypoxic and the hypercapnic ventilatory response, but its effects on the hypoxic and the hypercapnic cardiac response have not been reported. The purpose of this study was to determine if cardiac responses to hypoxemia and hypercapnia are altered by infusion of either dopamine (DOP) or its analog dobutamine (DBT). Baseline mean arterial blood pressure (MAP) and heart rate (HR) were measured in 7 normal male subjects while normal saline was infused intravenously (NS1) for 30 min. Each subject then underwent both a eucapnic hypoxemic challenge (EHC), and a hyperoxic hypercapnic challenge (HHC). In a double-blinded randomized fashion either DOP1 or DBT1 was selected and infused at 5 micrograms/kg/min for 30 min. EHC and HHC were again performed. This sequence was then repeated following a second NS infusion (NS2) and the alternate vasopressor. On a second study day, the dose of dopamine (DOP2) selected was that sufficient to induce a similar rise in MAP as seen with DBT1. Following NS and DOP1 there was a reproducible significant linear increase in HR with progressive hypoxemia seen in all subjects. This response was significantly augmented following infusion of DBT1 (p < 0.03), but no such augmentation was noted with DOP2. No significant change in HR was noted during HHC. The mechanisms responsible for this augmentation of hypoxemic response during dobutamine infusion are unclear, and do not appear to be related to a rise in MAP. We speculate that it is due to an effect of dobutamine on beta 1-receptor activity.

RF current density imaging in homogeneous media.

MRI has proven capable of imaging quasistatic volume current densities in electrolytic and biological media. In this paper, the feasibility of extending the method to image RF current density at the Larmor frequency is studied. RF current imaging could be relevant to MR power absorption and safety and to hyperthermia analysis, as well as creating dielectric and conductivity-dependent tissue contrast. The approach is to deliberately induce or inject RF currents in a sample synchronous with an MR pulse sequence and measure the resulting transverse RF magnetic field components. Current density is extracted by computing the curl of the magnetic fields. The preliminary theory has been developed for uniform media where both displacement and conduction currents exist while skin effects or eddy currents are absent. If the derivative in the B0 direction of the RF magnetic field component parallel to B0 is negligible, then sufficient information exists to reconstruct the RF current density component that is parallel to B0 without rotating the sample. The relative phase of the current can also be estimated. The method has been proven feasible by successfully imaging a uniform 85.6-MHz current density in a salt water phantom. The experiment conforms closely to capacitively coupled hyperthermia heating.

Comparison of six oxygen delivery systems for COPD patients at rest and during exercise.

Five different oxygen-conserving devices were tested in each of ten oxygen-dependent patients with COPD who had met the NOTT criteria for continuous oxygen use. They were tested on room air, their prescribed continuous oxygen flow and then on each of the five devices. The devices which delivered a bolus of oxygen during early inspiration or increased oxygen delivery as the respiratory rate increased did better than those devices which delivered oxygen at a normal flow rate during inspiration or a fixed portion of inspiration. In at least one of the subjects each device was associated with desaturation to less than 80 percent during a 12-min walk. It is concluded that oxygen-conserving devices vary in their ability to maintain SaO2 levels during exercise. It is recommended that a home oxygen evaluation include measurement of an exercise SaO2 utilizing the prescribed oxygen delivery system.

The role of antibiotics in the management of acute exacerbation of chronic bronchitis (answers to some commonly asked questions).

More than 7 million Americans suffer from chronic bronchitis, and it has been estimated that each of these patients will experience between one and four acute exacerbations a year. This problem constitutes a major social and financial burden on our society. Despite the prevalence of this disorder there is still considerable disagreement among physicians as to appropriate treatment, especially with regard to the use of antibiotics. Though the role of antibiotics is unclear, the pharmaceutical industry is trying to obtain regulatory approval of several new antibiotics for use in exacerbations of chronic bronchitis. We examine the role of antibiotics in the management of chronic bronchitis.

Transdermal delivery of the alpha 2-agonist clonidine does not alter airways responses to inhaled histamine or methacholine.

Previous studies have reported that the inhalation of the alpha 2-agonist clonidine decreases airways reactivity. Other studies have shown that oral doses of clonidine acutely increase airways reactivity to histamine, but not to methacholine. Recently, a transdermal clonidine delivery system (TTS) has been approved for use, and there is an increasing interest in using this system for management of postmenopausal and smoking cessation symptoms. To our knowledge, the effects of TTS on airways function in asthmatics have not been reported. The purpose of this study was to determine if use of TTS would alter airways reactivity. Six asymptomatic asthmatic subjects underwent a baseline methacholine challenge (M). In a double-blinded randomized crossover fashion, either a placebo or a TTS patch (TTS-1, 0.1 mg/day), was applied to the arm. Four days later, the challenge was repeated. After two to three days of washout, the alternate patch was applied, and a second challenge was performed. Several days later, a second baseline challenge was repeated. This sequence was then repeated using histamine (H). The patch was well tolerated by all subjects. There was no significant change in resting pulse or blood pressure, and for the group no change in airways reactivity to either M or H was noted. In conclusion, while use of TTS-1 does not improve airways function, its short-term use in asthmatics is not associated with an increase in airways reactivity.