Optimized gradient pulse for use with EPI employing active acoustic control.

The concept of active acoustic control was recently introduced by Mansfield and Haywood (MAGMA 2000:10:147-151) to ameliorate the problem of acoustic noise from MRI, particularly that from high-speed EPI. A 30 dB reduction in noise was previously achieved with the use of acoustic control operating at spot frequencies within a narrow band. In this work, a new acoustic gradient pulse is introduced that comprises an oscillating gradient of finite duration, incorporating a combination of frequencies within this band designed for use as the switched read gradient in echo-planar imaging (EPI). Employing this pulse with active acoustic control results in a reduction of acoustic noise by 50 dB.

Shielded gradients. And the general solution to the near field problem of electromagnet design.

The development of actively shielded gradients introduced the concept of surface distributed conductors for the production of electromagnetic fields. This represented the most significant step in electromagnetic coil design since the discovery of the electromagnetic field equations a century earlier. Further, the associated recognition of the Biot-Savart equation as the convolution of the current distribution function with the inverse square spatial dispersion, permits a solution of the general near field problem with implications for other scientific fields that have yet to be explored.

Effect of preflaring on Root ZX apex locators.

The Root ZX apex locator is an example of a generation of apex locators that identify the terminus of the canal by measuring a ratio between two electrical impedances. Studies have shown this device to have a high degree of accuracy. However, the manufacturer warns that the performance of these devices is limited by the presence of calcifications and dentinal shaving obstructions. An in vitro study was designed to determine if preflaring of canals would facilitate the passage of files to the apical foramen by eliminating cervical interferences and to see what effect this would have on the performance of the Root ZX apex locator. Thirty-two canals were divided into two groups. Group 1 was not manipulated before use of the Root ZX apex locator and served as control. In group 2, the canals were preflared before the use of the Root Zx apex locator. The working length files were secured in place and measured with the linear measurement tool used by the Visilog 5 imaging program. Results of this study suggest that preflaring of canals will allow working length files to more consistently reach the apical foramen (p = 0.015), which in turn increases the efficacy of the Root ZX apex locator.

Cardiac event recorders yield more diagnoses and are more cost-effective than 48-hour Holter monitoring in patients with palpitations. A controlled clinical trial.

OBJECTIVE: To compare the diagnostic yield and cost-effectiveness of transtelephonic event monitors with those of Holter monitoring in patients with intermittent palpitations. DESIGN: Randomized crossover trial. SETTING: Diagnostic service of a teaching hospital and surrounding primary care practices. PATIENTS: 43 patients with previously uninvestigated palpitations who were referred for Holter monitoring. MEASUREMENTS: Patients were randomly allocated to receive an event monitor or 48-hour Holter monitor and then to receive the other device. Event monitors were used for 3 months or until two recordings were obtained while symptoms occurred. The main end point was an electrogram recorded during symptoms. The incremental cost-effectiveness of obtaining a diagnostic rhythm strip from event monitors was compared with that of Holter monitoring. RESULTS: The mean (+/- SD) patient age was 45 +/- 19 years; 37 patients (88%) were women. Event monitors were twice as likely to provide a diagnostic rhythm strip electrocardiogram during symptoms as 48-hour Holter monitoring (29 patients [67%] and 15 patients [35%], respectively; P < 0.001). Event monitors detected 8 patients (19%) with clinically important arrhythmias (6 patients with supraventricular tachycardia and 2 with atrial fibrillation or flutter), whereas the Holter monitors detected no significant arrhythmia (P < 0.005). With the event monitors, most patients transmitted an electrocardiogram recording by 6 weeks. Event monitors were dominant and therefore more cost-effective than 48-hour Holter monitoring, resulting in a cost savings of $213 for each additional diagnostic rhythm strip obtained during symptoms. CONCLUSIONS: Holter monitoring is a poor diagnostic test for intermittent palpitations. Event recorders provide better data and are more cost-effective.

Active acoustic screening: reduction of noise in gradient coils by Lorentz force balancing.

We have designed and constructed a quiet gradient set with restricted access for the combined purposes of evaluating the principles of active acoustic screening, recently introduced by Mansfield, Glover, and Bowtell, and for EPI studies of the head at 3.0 T. The design utilizes the return paths of the conductors in a closed arc loop arrangement to eliminate net Lorentz forces thereby attenuating acoustic noise especially at low frequency. This design should significantly reduce the dangers to patients of high noise levels, especially in high field magnetic resonance imaging systems.

Adaptive Fourier threshold filtering: a method to reduce noise and incoherent artifacts in high resolution cardiac images.

We introduce an image processing method which reduces white noise and random artifacts in sets of high resolution, time resolved images. At each pixel, the processing consists of: 1) the isolation of a time intensity curve (TIC), 2) Fourier transformation of each TIC, 3) application of a threshold to remove low intensity coefficients, 4) inverse transformation to generate noise reduced TICs which are recombined to form images with improved signal-to-noise ratio (SNR). Noise filtering by Fourier thresholding is demonstrated on a set of cardiac images, resulting in a reduction of the noise energy by approximately 90%.

Granulomatous hepatitis in dogs: nine cases (1987-1990).

Granulomatous hepatitis (GH) is an uncommon histopathologic diagnosis in dogs. On the basis of clinical reports, fungal infections appear to be the most common cause of GH in dogs, but many other potential causes have been identified. The medical records and histopathologic findings for 9 dogs with GH were reviewed to identify additional specific causes of GH in dogs. Diseases associated with GH included intestinal lymphangiectasia (n = 2), lymphosarcoma (n = 1), histiocytosis (n = 1), dirofilariasis (n = 1), and histoplasmosis (n = 1). In 1 dog, no other disease process was identified. Of the remaining 2 dogs, 1 had concurrent granulomatous pneumonitis of unknown cause, and the other had periportal hepatitis and temporal muscle wasting. All 9 dogs with GH had clinical evidence of liver disease, such as hepatomegaly, icterus, and ascites, or had high serum alkaline phosphatase and alanine aminotransferase activity. Because of the wide variety of potential causes of GH in dogs, an accurate diagnosis should be sought so that appropriate treatment can be chosen and an accurate prognosis given.

Feline aggression. Classification, diagnosis, and treatment.

Types of aggressive behavior commonly recognized in cats include intermale, territorial, fear/defensive, play, predation, and redirected. Diagnosis is made on the basis of signalment data, the pattern of aggressive postures displayed by the aggressive cat, and the circumstances in which the aggressive behavior occurred. Treatment varies with the type of aggressive behavior but may include neutering, desensitization and counter-conditioning techniques, punishment, drug therapy, and management changes.

Behavioral problems in old dogs: 26 cases (1984-1987).

Among 26 dogs greater than or equal to 10 years old, the most frequent owner complaints relating to behavioral problems were destructive behavior in the house (n = 10), inappropriate urination or defecation in the house (n = 10), and excessive vocalization (n = 7). The most frequent behavioral diagnoses were separation anxiety (n = 13) and breakdown of housetraining (n = 6). Most of the behavioral problems in the 26 dogs began after the dogs reached the age of 10 years, and most of the dogs had been owned for many years without having behavioral problems. Few behavioral problems in old dogs had a medical basis. Most cases of inappropriate urination or defecation in the house were not related to urinary or fecal incontinence, but were exacerbated by problems such as degenerative joint disease and renal disease. Behavioral therapy is appropriate for behavioral problems in old dogs, and, taking into account an old dog's health and physical limitations, techniques used are the same as for younger dogs.

Cat aggression redirected to people: 14 cases (1981-1987).

Among 27 cases of cat aggression manifested toward people, 14 cases were diagnosed as redirected or probable redirected aggression, because the cat was already highly aroused by other stimuli before attacking a person. A detailed behavioral history enabled identification of arousing stimuli. The most common arousing stimulus was the presence of another cat. Other arousing stimuli included high-pitched noises, visitors in the house, a dog, an unusual odor, and being outdoors unexpectedly. Medical problems or other behavioral abnormalities were not detected in any of the cats that could explain their aggressive behavior. Management consisted of avoidance or elimination of arousing stimuli wherever possible and extensive client education. On follow-up there was no recurrence of redirected attacks in 4 cats, variable decreases in the severity and frequency of attacks in 5 cats, and no change in 1 cat. Three cats were euthanatized, including one that had shown some improvement. Follow-up information was not available for the 2 remaining cases. Redirected aggression in cats is not well documented and may be misdiagnosed as idiopathic aggression or other behavioral abnormality. Although redirected attacks may be sudden, severe, and frightening, with careful management, a favorable outcome is possible.

A comparison between two types of waveform analysis in patients with multisegmental arterial disease.

The results of an experiment to compare two different methods of analysing ultrasound signals are presented. Normal volunteers, both young and old, and patients with arteriosclerosis were examined with Doppler shifted ultrasound and the results of two forms of waveform analysis retrospectively compared with angiograms. The angiograms were used to divide the patients into groups with similar patterns of disease. The ability of the two methods of analysis, 'pulsatility Index' (PI) and 'Laplace transform damping factor' (LTD), to identify patients with haemodynamically significant disease in the aorta or iliac arteries was tested statistically (Mann-Whitney U test) and compared in receiver operator curves. The results showed that both tests were equally good in the identification of aortoiliac disease, even when the superficial femoral artery was occluded, and that, contrary to theoretical arguments, LTD was influenced by distal impedance.

An investigation into how the geometry of an end-to-side arterial anastomosis affects its function.

The effects of altering the geometry of an end-to-side junction were investigated in a hydraulic model. The dimensions of the tubes, pressures and flow rate and the frequency of pulsation were calculated by dimensional analysis, to produce a model which simulated pulsatile flow in small arteries. The ratio between the impedance of the 'bypass' and the impedance downstream from the junction was greater than unity when the two tubes forming the junction were of unequal diameter. No increase in downstream impedance was measured when the angle of junction was increased from 45 degrees to 135 degrees. Cine photographs of streamlines at the junction showed that flow passed smoothly through the junction irrespective of angle and that perturbations occurred only during that part of the cycle when flow was reversed. The results indicate that the angle at which a junction is made affects flow. The effect is small and is only seen when the ratio of diameters of the tubes is unity. The ratio of the diameters of the two tubes which make up the junction has the greatest effect on flow through the junction.

The mechanical properties of glutaraldehyde stabilized human umbilical vein measured in vivo.

Vascular prostheses, when used to bypass the femoral and popliteal arteries, and particularly if the bypass is made to the distal part of the tibial arteries, seldom remain patent, or if they do then for only a limited period of time. Femorotibial bypass with modified human umbilical vein is relatively successful in selected patients and one explanation may be that it resembles human arteries more than other prostheses. We have developed a method of calculating the asymptotic phase speed, from the propagation constant and from this the characteristic impedance of a bypass (all of which characterize viscoelastic behaviour). Calculations were made on measurements of pressure made in vivo. Twenty patients who had a femorotibial bypass, using glutaraldehyde stabilized umbilical vein, were studied and, from measurements of pressure made at operation, we calculated the asymptotic phase speed and the characteristic impedance of the prostheses. Results show that the viscoelastic properties of newly implanted umbilical vein are comparable to those of autogenous saphenous vein.

An in vivo method of measurement of the mechanical properties of vascular prostheses: the mechanical properties of saphenous vein bypass grafts.

It seems likely that long term patency of small bore vascular prostheses is dependent upon, among other things, the mechanical properties of their walls. Arteries are visco-elastic but there is no accurate method of measuring the visco-elasticity of arterial substitutes in vivo. The most successful vascular substitute is autogenous saphenous vein and it is essential to know its elastic properties if we are to mimic them in prostheses. (veins rapidly lose their elasticity when excised and measurements made in vitro are unrealistic.) We describe an in vivo method which is based on measurements of pressure alone from which we calculate a propagation constant and phase speed, which characterises the visco-elastic behaviour of vein. Sixteen patients who had a femoro-popliteal bypass were studied. Measurements of pressure were used to calculate the phase speed of the pulse and the relationship of phase speed to frequency was calculated. The asymptotic phase speed for human saphenous vein was 13.6 m s-1.

Perforated peptic ulcer long-term follow-up.

A series of 349 survivors of perforated peptic ulcer was followed for periods of up to 23 years. Almost nine out of every 10 patients suffered from dyspepsia during follow-up. Subsequent elective gastroduodenal surgery was required in more than a quarter of the cases. The surgery rate for gastric ulcer was more than one and a half times that for pyloroduodenal ulcer, and for females almost double that for males. The highest rate of all was for females with gastric ulcer, of whom almost one half came for surgery. One in five patients bled during follow-up. One in eight developed stenosis of the stomach of duodenum, and one in 11 perforated again. There was a significantly increased incidence of subsequent perforation and stenosis in those with an initial perforation of 5 mm or more in diameter. Gastric carcinoma occurred in less than 2% of cases and was restricted to cases of pyloroduodenal perforation. When complications occurred, the majority did so within five years. Only 15% of the 262 patients about whom complete information was available had no complications on follow-up. The indications for definitive surgery at perforation should be extended to include perforated gastric ulcer in the female, particularly if the ulcer is large.

Measuring the response of the jejunal mucosa in adult coeliac disease to treatment with a gluten-free diet.

A previously described technique for measuring changes in the architecture of the small intestinal mucosa was used to measure the long-term response in six patients with adult coeliac disease to treatment with a gluten-free diet. All had flat or flat-with-mosaic jejunal mucosae before treatment and were subsequently believed to keep strictly to a gluten-free diet. They were followed for between four and 14 months from the start of treatment. The ratio of the area of surface epithelium to that of crypt epithelium (;area ratio') invariably increased following gluten withdrawal, but did not begin to do so until after several weeks of treatment. No patient attained complete histological normality within the limited period of observation, which was never more than 14 months. In one of the three patients followed for a year or more the area ratio increased to within the control range, and in two of these three the ratio was about 10 times the pretreatment ratio. There was a highly significant linear correlation between area ratio and time on the diet (r = 0.775, p < 0.005). The surface cell height measurements for these patients, by contrast, rose steeply and almost invariably during the first few weeks of treatment, but after that they fluctuated without further significant change. It is suggested that the two methods of measurement were complementary to each other, surface cell height being useful while the patient was in hospital on a rigidly strict diet, and the area ratio after return home, when minor dietary lapses were almost invariable.

A new technique for examining intestinal biopsies.

A new technique for measuring changes in the architecture of the small intestinal mucosa is described using a modification of the technique of television image analysis to measure the areas occupied by the surface and crypt epithelium in proximal jejunal biopsies. The ratios of these two areas to each other were then calculated. In 12 control mucosae, the mean ratio (+/-SD) was 2.27 +/- 0.41. In 12 untreated flat mucosae, by contrast, the mean ratio was only 0.24 +/- 0.07. This ten-fold difference, which was highly significant (p < 0.001), was greater than that for any similar measurements previously reported. This technique is intended for the measurement of changes in the mucosa too small for existing techniques to detect reliably rather than for the diagnosis of coeliac disease.