Biomedical subjects

F S Prato

Publications and source records attributed to F S Prato.

At least 73 records · Page 4Linked to original sources

PubMed1988

Serial nuclear magnetic resonance imaging of acute myocardial infarction with and without reperfusion.

To compare nuclear magnetic resonance (NMR) image-derived T1 and T2 changes during evolving infarction, 14 dogs were studied serially: (1) 1 to 2 hours after left anterior descending coronary occlusion, (2) 2 to 3 hours after coronary occlusion (n = 7) or in the first hour after reperfusion following 2 hours of occlusion (n = 7), and (3) 5 days and (4) 21 days after occlusion/reperfusion. In addition, the extent of T1 and T2 abnormalities was compared to the extent of infarction as determined histologically for each set of images. With sustained coronary occlusion, an increase versus control values (T1 = 351 +/- 11 msec; T2 = 41 +/- 2 msec) was observed in the second hour after occlusion (T1 = 448 +/- 51 msec; T2 = 51 +/- 8 msec), gradually reaching a maximum by day 5 (T1 = 490 +/- 64 msec; T2 = 63 +/- 9 msec). By 21 days, T1 had decreased to 427 +/- 43 msec and T2 to 55 +/- 11 msec. However, with myocardial reperfusion, an abrupt increase in both T1 and T2 occurred compared to prereperfusion values in the first hour after release of occlusion, from 445 +/- 32 msec to 555 +/- 65 msec and from 52 +/- 5 msec to 65 +/- 8 msec, respectively. Subsequently, T1 remained elevated whereas T2 normalized. Only on day 21 images was there a good correlation between the extent of T1 and T2 abnormalities and infarct size, in both nonreperfused (r = 0.87; p less than 0.05), and reperfused (r = 0.89; p less than 0.01) dogs.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1988

Comparison of the biodistribution of gadolinium-153 DTPA and technetium-99m DTPA in rats.

Twenty-three mature Sprague-Dawley male and female rats were simultaneously injected with trace quantities of [153Gd]DTPA and [99mTc]DTPA and 0.5 mmol/kg of nonradioactive gadolinium DTPA. Rats were killed at 1 min, 5 min, 10 min, 15 min, and 30 min after the intracardiac bolus injection. The heart, lungs, liver, brain, kidney, and blood were excised and counted in a well-counter to determine the amount of the injected material in each organ and blood. In order for the percent of total injected activity to be determined, a technique was developed which allowed discrimination of the 140 keV gamma-ray of 99mTc from sum peaks of 153Gd when the latter is counted in a well-counter with 4 pi geometry. Although the distribution of the two DTPA compounds was qualitatively similar, statistical analysis indicated that the amount of 99mTc deposited in the lungs was higher than 153Gd (p = 0.03), the amount of 99mTc deposited in the kidneys was lower than 153Gd (p = 0.0004) and the amount of 99mTc in the blood was higher than 153Gd (p = 0.0022). This may be due to the greater binding of [99mTc]DTPA or its minor impurities to plasma proteins.

Animals↗

PubMed1987

Diagnostic applicability of magnetic resonance imaging in assessing human cardiac allograft rejection.

To assess the diagnostic applicability of magnetic resonance imaging (MRI) for diagnosis of cardiac allograft rejection, 25 patients who recently underwent cardiac transplantation were studied on a 0.15-tesla resistive system within 24 hours of endomyocardial biopsy. Ten normal volunteers and 4 patients who had recent (within 2 weeks) nontransplant cardiac surgery were also studied. In the 19 transplant patients imaged within 24 days of graft implantation, only 1 had evidence of graft rejection on biopsy. However, all nonrejecting grafts had increased T1 and T2 values, 501 +/- 22 and 61 +/- 6 ms, respectively (mean +/- standard deviation) and the only rejecting graft had values of 496 and 60 ms, respectively. In the normal volunteers mean T1 was 352 +/- 18 ms and T2 was 35 +/- 6 ms. There was no significant difference in T1 and T2 values between patients who underwent nontransplant surgery and control subjects. In patients with nonrejecting transplants who were imaged more than 25 days after surgery, the T1 and T2 values had normalized to 359 +/- 17 ms and 36 +/- 7 ms, respectively (n = 28 images in 20 patients). However, in those grafts with rejection, T1 and T2 were both elevated to 502 +/- 21 ms and 62 +/- 6 ms, respectively (n = 15 in 13 patients); wall thickness was also increased. Fourteen of 15 late rejection events (more than 25 days after surgery) were correctly identified on the basis of increases in T1 and T2 to more than 2 standard deviations above normal.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗

PubMed1987

Magnetic resonance imaging temporarily alters blood-brain barrier permeability in the rat.

Exposure to a short (23.2 min) standard clinical magnetic resonance imaging (MRI) procedure elicits a temporary dysfunction of the blood-brain barrier in rats. Monitoring of the increased permeability of rat brain frontal cortex microvessels with the protein tracer horseradish peroxidase and freeze-fracture electron microscopy, revealed an amplified vesicle-mediated transport of tracer across the microvessel endothelium to the albuminal basal lamina and extracellular compartment of the brain parenchyma. Recovery of normal blood-brain function, as evidenced by exclusion of protein tracer from subendothelial basal lamina and neuropil extracellular milieu, was complete 15-30 min following cessation of the MRI exposure. These findings raise the possibility that exposure to clinical MRI procedures may also temporarily alter central blood-brain permeability in human subjects.

Animals↗

PubMed1987

Cardiac T1 calculations from MR spin-echo images.

Normally, cardiac triggering in MR spin-echo imaging restricts repetition times (TR) to integral values of the cardiac period (TC), and introduces irregularities in TR due to variations in TC. We have investigated how much these restrictions decrease the accuracy and precision of spin-lattice relaxation (T1) values of the myocardium calculated from two cardiac-triggered spin-echo images. By introducing additional excitation pulses, TR can effectively be reduced to a fractional value of TC and considerable improvement in T1 precision is possible. For TC = 800 ms, the improvement in T1 precision is 30% when two spin-echo images of TR = 1/2 X TC and TR = 2 X TC are used to calculate T1 instead of two images with TR = TC and TR = 2 X TC. The irregularities in TR decrease both T1 precision and accuracy. Irregularities of the order of 15% in a mean TR of 800 ms produce a fourfold decrease in precision. Since irregularities in TC easily exceed 15%, MRI data should be acquired when individual TR values are approximately within +/- 15% of the subject's mean TC.

Animals↗

PubMed1987

An optimized head coil design for MR imaging at 0.15 T.

Receive-only head coils employing a modified solenoid design were developed for a 0.15-T imager with horizontal main static and radiofrequency transmit fields. This coil design uses three or five identical horseshoe-shaped elements, constructed of 1/2-in. outside diameter copper tubing, lying one above the other in equally spaced horizontal planes. Coils of this design were compared to the half-saddle coil supplied with our imager and to the Hammersmith Hospital spherical coil (G.M. Bydder et al., J. Comput. Assist. Tomogr. 9, 987 (1985]. Compared to the half-saddle coil, one of our new head coils has the same field of view while improving the signal-to-noise ratio (S/N) by 80% in the upper brain and 20% in the cervical vertebrae; compared to the spherical coil the S/N was up to 60% lower but the field of view was larger and patient comfort was better.

Brain↗

PubMed1987

The effect of magnetic resonance imaging on human cognition.

Potential effects of MRI exposure on aspects of human cognition were investigated out of concern that possible safety hazards associated with the procedure may exist. One hundred and fifty-seven volunteer subjects were randomly assigned to either an imaged, sham-imaged or nonimaged control condition. The following psychological tests were administered in a double blind procedure at pretreatment, post-treatment and follow-up time periods: the Wechsler Adult Intelligence Scale-Revised (Digit Span, Block Design and Digit Symbol), the Wechsler Memory Scale Paired Associate Learning test, the Benton Revised Visual Retention test, the Vandenberg Mental Rotation test, the Sternberg memory scanning paradigm and the State Anxiety Inventory. The overall analysis of results indicated that MRI at 0.15 T has no significant effect upon the cognitive functions assessed.

Adolescent↗

PubMed1987

Attenuation of morphine-induced analgesia in mice by exposure to magnetic resonance imaging: separate effects of the static, radiofrequency and time-varying magnetic fields.

Exposure of adult male mice to a magnetic resonance imaging (MRI) procedure has been shown to abolish the nocturnal analgesic responses observed following treatment with morphine. The field component(s) responsible for this inhibitory effect were examined by exposing mice to either the static, time-varying or rf magnetic field components associated with an MRI procedure. In the middle of the night portion of their day-night cycle, mice were exposed for 23.2 min to one of the above field components, intraperitoneally injected with morphine sulphate (10 mg/kg) and then exposed to the field conditions for another 23.2 min, after which analgesic responses were determined. Analgesia was quantitated by determining the length of time mice were content to be on a hot surface (50 degrees C) before they showed discomfort by licking their paws. It was observed that the time-varying magnetic field completely abolished, the rf field significantly reduced, while the static field component (0.15 T) had no evident effect on morphine-induced analgesia. These results indicate that the time-varying, and to a lesser extent the rf, fields associated with the MRI procedure inhibit morphine-induced analgesia in mice. These data also raise the possibility that exposure in humans to some of the magnetic field components associated with MRI may have clinically relevant effects on the actions of narcotic drugs such as morphine.

Animals↗

PubMed1987

Survivability and long-term stress reactivity levels following repeated exposure to nuclear magnetic resonance imaging procedures in rats.

The effect of exposure to the magnetic and radio-frequency fields associated with Nuclear Magnetic Resonance Imaging (MRI) on survivability and long-term stress reactivity levels was examined in male rats. Rats in the experimental condition were exposed to MRI for 22.5 minutes for five successive days (Expt. 1) or 23.3 minutes for twenty-one successive days (Expt. 2). Sham field exposed animals received the identical treatment as the exposed animals except that the magnetic and radio-frequency fields were absent. Control rats were also maintained. Thirteen to twenty-two months after the exposure procedure the remaining rats were sacrificed and their whole body, spleen, heart, thymus, and adrenal weights were recorded. Blood samples were taken for measurements of red and white blood cell counts, hemoglobin content, as well as adrenocorticotrophin and corticosterone levels. The results fail to provide any evidence for changes in survivability and long-term stress reactivity levels in rats exposed to MRI and thus give no grounds to challenge the view that MRI is a safe diagnostic procedure.

Adrenocorticotropic Hormone↗

PubMed1986

Optimization of signal-to-noise ratio in calculated T1 images derived from two spin-echo images.

A simplified model relating signal intensity in an MR image to spin-lattice relaxation time (T1), repetition time (TR), number of signal averages and the average tip angle (-alpha) of the protons within the slice has been developed. This model has been used to select the optimal repetition times of two spin-echo images for a fixed total imaging time to maximize signal to noise in calculated T1 images. Theoretical predictions of T1 are virtually identical to spectroscopically measured values, and the relative noise (delta T1) in T1 images calculated from two measured spin-echo images is in good agreement with the theoretically predicted values of delta T1/T1. This model predicts that: (a) for a T1 of approximately 500 ms, the least T1 image noise is obtained with one of the spin-echo images collected with a TR of 400-500 ms. The longer the TR of the other spin-echo image, the lower the T1 image noise, but past a TR of approximately 1400 ms, T1 image signal/noise is optimized for the same total imaging time by increasing the number of averages in the shorter TR spin-echo image rather than increasing the TR of the second spin-echo image. (b) The error is reduced and the optimum TR1 is reduced as -alpha is increased from 63 to 90 degrees. (c) For a range of T1, optimal selection of TR1 and TR2 based on an intermediate value of T1, results in relatively little increase over optimal values in delta T1/T1 for the entire T1 range.

Humans↗

PubMed1986

Behavioral effects of exposure to nuclear magnetic resonance imaging: I. Open-field behavior and passive avoidance learning in rats.

The effect of exposure to the magnetic and radio-frequency fields associated with Nuclear Magnetic Resonance Imaging (MRI) on two standard animal behavior tests, was examined in rats. In the first experiment male rats were given a baseline open-field test and 48 hrs later exposed for 22.5 min to a MRI procedure, a sham imaging procedure, or a control condition. Immediately after this exposure period a second open-field test was administered. All animals were given 4 more daily exposures to their respective treatment conditions and after the last exposure period a third open-field test was given. Analysis of open-field ambulation, rearing, and defecation responses indicated no significant effect of exposure to MRI on these behaviours. In a second experiment rats were conditioned in a step-down passive avoidance task and then exposed for 23.2 min (48 hrs later) to MRI, sham imaging, or control conditions. Retention tests for the passive avoidance response were administered after the first and fifth daily exposure to the experimental treatment conditions. No significant effects of the treatment conditions on retention of the avoidance response were obtained and a third retention test 3 months after the second test, also failed to provide any evidence for treatment effects. These results fail to provide any evidence for short or long term behavioral changes in animals exposed to MRI.

Animals↗

PubMed1986

Behavioral effects of exposure to nuclear magnetic resonance imaging: II. Spatial memory tests.

In order to determine possible effects of exposure to nuclear magnetic resonance imaging (MRI) on cognitive processes, the performance of imaged, sham exposed, and control rats on a spatial memory task was examined. This particular task was chosen because, under some conditions, animals use the magnetic field as a compass when navigating. The rats were required to collect food from eight different locations before returning to an already chosen location. All three groups of rats achieved a high level of performance, and there were no differences between groups in any of the performance measures examined. These results indicate that the MRI procedure has no significant effect on spatial memory processes in rats.

Animals↗

PubMed1986

Serial imaging of canine myocardial infarction by in vivo nuclear magnetic resonance.

Anterior infarction was produced in eight dogs to characterize serial changes in nuclear magnetic resonance signal intensity within the infarct zone. Magnetic resonance imaging was done on the day of infarction, on day 4, 5 or 6, on day 13 and day 20 using a 0.15 tesla (6.25 MHz) resistive imager. Electrocardiographically triggered spin echo (30, 45 and 60 ms echo times) and inversion recovery (400 to 500 ms inversion time) pulse sequences were employed to obtain single slice images. On day 20, the excised hearts were sectioned and examined to determine infarct location and extent. In the spin echo images, signal intensity within the ischemic zone was visibly increased in seven of the eight dogs on the day of infarction, and in all dogs by days 4 to 6. Signal intensity remained elevated in all but two dogs at day 20. With inversion recovery imaging, changes in the infarct zone were highly variable; both ill defined increases and decreases in signal intensity were noted. With a 30 ms echo time, signal intensity in the infarct zone was increased on average 29.8 +/- 24.1% above that in normal myocardium on the day of infarction. The relative signal intensity increased to 62.4 +/- 23.5% during the first 2 weeks after infarction (p less than 0.05), then decreased to 12.0 +/- 18.5% by day 20 (p less than 0.05). Similar changes were detected in the images using the 45 and 60 ms echo times. Nuclear magnetic resonance imaging therefore is able to detect regions of myocardial infarction and follow evolutionary changes in signal intensity within the infarct zone with healing.

Animals↗

PubMed1986

Comparison of respiratory triggering and gating techniques for the removal of respiratory artifacts in MR imaging.

Respiratory movement degrades magnetic resonance (MR) images of the chest and abdomen by increasing noise through the production of "ghost" artifacts and by decreasing edge sharpness in moving structures. Respiratory gating, which limits data acquisition to end-expiration, is successful in restoring edge sharpness and reducing ghosts but increases imaging time two to three times, which limits its use to sequences with short repetition times (TRs). To overcome this limitation, an alternative technique, respiratory triggering, was developed, which triggers the acquisition of an MR section at a fixed point on the respiratory cycle. This technique restores edge sharpness and reduces ghosts, but unlike gating, it can be used to produce an image at any phase of the respiratory cycle. Triggering requires long TRs since the TR is limited to the respiratory period (TP) or one-half of TP, depending on whether the same section is triggered once or twice during a single respiratory cycle. Gating and triggering were evaluated and compared for single-section and multi-section imaging of both volunteers and patients. The authors conclude that when a chest or abdominal survey is required, triggering takes less time than gating if TRs are required that exceed one-fifth of TP.

Abdomen↗

PubMed1986

Hazards and associated recommendations for Canadian MR imaging sites.

The recent national survey reported here indicates that the use of magnetic resonance (MR) imaging in Canada for medical diagnosis may rapidly become widespread. However, the technique involves a number of potential hazards to patients, operating staff and the general public. MR involves exposure to magnetic and radiofrequency fields which may have biological effects, indicating a need for guidelines on acceptable limits of exposure for both patients and operating personnel. Other hazards include effects on cardiac pacemaker function, effects on other medical equipment important for patient management, dislodgement of metallic surgical clips, induced heating of tissue or metallic implants, danger of ferromagnetic objects becoming projectiles and a risk of asphyxiation if a superconducting magnet quenches. The recommendations in the report are practical guidelines to minimize these risks and hazards.

Accident Prevention↗

PubMed1985

Cardiovascular applications of magnetic resonance imaging.

Magnetic resonance (MR) imaging is a unique imaging modality that is gaining rapid acceptance for a variety of medical indications. Diagnostic information is obtained noninvasively, without the potential hazards of ionizing radiation. The spatial resolution and anatomic detail of MR imaging rival those of other currently available imaging methods. By gating to an electrocardiographic signal cardiac imaging is possible. Since March 1983 the authors have had experience with cardiac MR imaging in both animals and humans. Cardiac anatomy is well shown by this technique, which allows detection and characterization of intracardiac masses, congenital heart disease and anomalies of the great vessels. Myocardial infarction has been detected in both animals and humans without the use of contrast agents, and acute cardiac transplant rejection has been visualized in an animal model. Limitations of MR imaging primarily have been lengthy imaging times and the sensitivity of the images to motion. With further investigation and experience this technique may become useful for studying a wide variety of cardiovascular disorders.

Animals↗

PubMed1985

Exposure to nuclear magnetic resonance imaging procedure attenuates morphine-induced analgesia in mice.

Adult male mice exposed to a Nuclear Magnetic Resonance Imaging (NMRI) procedure during the mid-dark period and injected with morphine (10 mg/kg) failed to exhibit the normal nocturnally enhanced morphine analgesia response to a thermal stimulus that was displayed by mice exposed to a sham imaging procedure and treated with morphine (p less than .01). When tested during the mid-light period, animals exposed to the NMRI procedure and given morphine displayed attenuated analgesia levels relative to sham exposed mice (p less than .01) treated with morphine. However, the morphine induced analgesia was not totally abolished since the imaged mice still exhibited analgesia relative to saline treated mice (p less than .01). These results suggest that the magnetic and/or radio-frequency fields associated with the NMRI procedure alter both day- and night-time responses to morphine. These results may reflect magnetic field induced alterations in neuronal calcium binding and/or alterations in nocturnal pineal gland activity.

Analgesia↗

PubMed1985

Dopamine: its potential for inducing ischemic left ventricular dysfunction.

As an agent potentially capable of inducing ischemia in patients with coronary artery disease, dopamine administered intravenously was evaluated as a pharmacologic stress agent by supine radionuclide angiography, and the results were compared with ergometer exercise. In a preliminary group of 11 subjects (4 normal subjects and 7 patients with coronary disease), dopamine alone was administered in increments of 2.5 micrograms/kg per min to a maximum of 15 micrograms/kg per min. There were significant differences between exercise and dopamine in maximal stress heart rates, 129.3 +/- 30.0 versus 88.0 +/- 35.8 beats/min (p less than 0.05) in normal subjects and 118.9 +/- 21.1 versus 87.6 +/- 22.6 beats/min (p less than 0.05) in patients with coronary disease, as well as in maximal stress rate-pressure products, 213.3 +/- 51.4 versus 155.0 +/- 52.5 mm Hg/min X 10(2) (p less than 0.02) in normal subjects and 216.0 +/- 45.6 versus 161.0 +/- 48.6 mm Hg/min X 10(2) (p less than 0.003) in patients with coronary disease. As a result, in these patients the ejection fraction response was significantly different: -3.3 +/- 4.5% with exercise versus + 6.3 +/- 4.6% with dopamine (p less than 0.05). In a second group of 41 subjects (9 normal subjects and 32 patients with coronary disease), atropine (0.6 mg) was administered intravenously before and after every second dopamine dose increment. This produced statistically similar maximal stress heart rates as compared with exercise in all subjects, rate-pressure products in normal subjects and slightly higher values with dopamine in patients with coronary disease: 200.3 +/- 47.2 versus 183.1 +/- 43.0 (p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Abdominal Muscles↗