Spin lattice relaxation time measurements in two-dimensional nuclear magnetic resonance imaging: corrections for plane selection and pulse sequence

Accurate determination of relaxation times has become increasingly important in efforts to determine the diagnostic specificity of nuclear magnetic resonance (NMR) imaging. Techniques used in NMR imaging, not routinely employed in conventional NMR spectroscopy, can significantly affect the resulting relaxation time determinations. For the saturation recovery (SR) approach of T1 measurement used in our laboratory, these include selective excitation to define the image plane and magnetization refocusing for NMR signal acquisition. Computer modeling of the Bloch equations shows that errors well over 50% can be made in image derived T1 measurements if the conventional SR relation between signal intensity and the 90-90 degrees interpulse delay, tr, is used. However, corrected expressions can be derived for the actual pulse and gradient sequence used by our imaging system, and phantom data acquired in imaging experiments have verified the validity of these equations. This allows for the correction of T1 data to compensate for systematic bias introduced during imaging procedures and suggests a means whereby errors introduced by radio frequency inhomogeneities across the imaging volume can be reduced.     

Radionuclide wall motion study and ejection fraction in clinical practice

Assessment of ventricular function is important in diagnosis and as a predictor of survival in many cardiopulmonary disorders, and analysis of ventricular function is one of the oldest applications of radioactive tracers in medicine. A sequence of parallel developments in instrumentation, radiopharmaceuticals, and nuclear medicine computers has allowed implementation of accurate, sensitive, noninvasive techniques for analysis of both right and left ventricular function. Techniques, indications, applications, and information that can be obtained are discussed.     

Nuclear magnetic resonance imaging in evaluation of clinical stroke syndromes

Proton nuclear magnetic resonance (NMR) imaging was performed on normal volunteers and patients with various types of clinical strokes. True three-dimensional volumetric data were obtained for subsequent reconstruction of images at various orientations, including transverse, coronal, and sagittal, and for specific matching to x-ray computed tomographic planes. A variety of radiofrequency pulse sequences was used to generate images weighted by the NMR parameters spin density (p) and spin-lattice (T1) and spin-spin (T2) relaxation times. Quantitative T1 data and qualitative T2 information were obtained from appropriate sequences. Proton NMR images embodying T1 information provided adequate delineation of normal intracranial anatomical structure and a high level of gray matter-white matter contrast; high lesion detection sensitivity in various clinical forms of stroke was seen in images providing both T1 and T2 information. T1 and T2 relaxation times were prolonged in embolic, thrombotic, and watershed infarctions as well as in lacunae; shortening of T1 and T2 was found in hematomas. Serpiginous vessels in an arteriovenous malformation were seen that had particular pulse sequences.     

Comparison of dietary fat and fatty acid intake estimated by the duplicate diet collection technique and estimated dietary records

Introduction A high saturated fatty acid intake is a well recognized risk factor for coronary heart disease development. More recently a high intake of n‐6 polyunsaturated fatty acids (PUFA) in combination with a low intake of the long chain n‐3 PUFA, eicosapentaenoic acid and docosahexaenoic acid has also been implicated as an important risk factor. Aim To compare total dietary fat and fatty acid intake measured by chemical analysis of duplicate diets with nutritional database analysis of estimated dietary records, collected over the same 3‐day study period. Methods Total fat was analysed using soxhlet extraction and subsequently the individual fatty acid content of the diet was determined by gas chromatography. Estimated dietary records were analysed using a nutrient database which was supplemented with a selection of dishes commonly consumed by study participants. Results Bland & Altman statistical analysis demonstrated a lack of agreement between the two dietary assessment techniques for determining dietary fat and fatty acid intake. Conclusion The lack of agreement observed between dietary evaluation techniques may be attributed to inadequacies in either or both assessment techniques. This study highlights the difficulties that may be encountered when attempting to accurately evaluate dietary fat intake among the population.     

Regional specificity of exercise and calcium during skeletal growth in girls: a randomized controlled trial.

Combining exercise with calcium supplementation may produce additive or multiplicative effects at loaded sites; thus, we conducted a single blind, prospective, randomized controlled study in pre- and early-pubertal girls to test the following hypotheses. (1) At the loaded sites, exercise and calcium will produce greater benefits than exercise or calcium alone. (2) At non-loaded sites, exercise will have no benefit, whereas calcium with or without exercise will increase bone mass over that in exercise alone or no intervention. Sixty-six girls aged 8.8 +/- 0.1 years were randomly assigned to one of four study groups: moderate-impact exercise with or without calcium or low-impact exercise with or without calcium. All participants exercised for 20 minutes, three times a week and received Ca-fortified (434 +/- 19 mg/day) or non-fortified foods for 8.5 months. Analysis of covariance (ANCOVA) was used to determine interaction and main effects for exercise and calcium on bone mass after adjusting for baseline bone mineral content and growth in limb lengths. An exercise-calcium interaction was detected at the femur (7.1%, p < 0.05). In contrast, there was no exercise-calcium interaction detected at the tibia-fibula; however, there was a main effect of exercise: bone mineral content increased 3% more in the exercise than non-exercise groups (p < 0.05). Bone mineral content increased 2-4% more in the calcium-supplemented groups than the non-supplemented groups at the humerus (12.0% vs. 9.8%, respectively, p < 0.09) and radius-ulna (12.6% vs. 8.6%, respectively, p < 0.01). In conclusion, greater gains in bone mass at loaded sites may be achieved when short bouts of moderate exercise are combined with increased dietary calcium, the former conferring region-specific effects and the latter producing generalized effects.     

Post-laparoscopic cholecystectomy bilomas--preliminary experience.

The incidence of biloma formation after laparoscopic cholecystectomy (LC) is, in the early experience of many centres, significantly higher than after open cholecystectomy. We describe four cases representative of the possible spectrum of post-LC bile leaks and review the literature regarding the radiologic investigation and management of this complication. We suggest that post-LC bilomas should initially be drained percutaneously. Endoscopic cholangiography (ERC) should then be used to identify the source of the leak, but sphincterotomy and/or stent placement may be best reserved for those whose leaks do not resolve after 10 days of free drainage. Surgery is recommended only for major biliary injury and for leaks that remain unresolved after sphincterotomy and/or stenting. An algorithmic summary of this approach is presented.     

Recombinant caprine 3H-[N-Acetylglucosamine-6-Sulfatase] and human 3H-[N-Acetylgalactosamine-4-Sulfatase]

The use of recombinant lysosomal enzymes for enzyme replacement therapy (ERT) is likely to be a necessary component of effective treatment regimens for lysosomal storage diseases (LSDs). The mechanism and rate of uptake into target cells, rate of disappearance of the enzyme from plasma, and its tissue distribution are important factors to assess the need for possible modifications to the enzyme, particularly for LSDs that affect the central nervous system (CNS). Two recombinant lysosomal enzymes, caprine N-acetylglucosamine-6-sulfatase (rc6S) and human N-acetylgalactosamine-4-sulfatase (rh4S), deficient in MPS IIID and MPS VI, respectively, were radiolabeled and purified. The major portion (>77%) of each recombinant enzyme contained the mannose-6-phosphate (M6P) recognition marker as demonstrated by their ability to bind to a M6P receptor affinity column. The uptake of ³H-rc6S and ³H-rh4S into cultured rat brain cells was also inhibited by the addition of 5 mM M6P to the culture medium. After iv administration of 0.4–0.5 mg/kg of ³H-rc6S and 1 mg/kg of ³H-rh4S to the rat, both enzymes were rapidly lost from the circulation in a biphasic fashion (t _1/2 for ³H-rc6S=1.25±0.15 min and 37.17±23.29 min; t _1/2 for ³H-rh4S=0.41 and 5.3 min). At this dose, about 6% of ³H-rc6S, but only 0.49% of ³H-rh4S, remained in the plasma 4 h after administration, whereas approx 30% of ³H-rc6S and more than 50% of ³H-rh4S was found in the liver. At doses of 1.6–2.0 mg/kg of ³H-rc6S and 1 mg/kg ³H-rh4S, but not at the lower dose of ³H-rc6S, trace levels of both ³H-rc6S and ³H-rh4S were detected in the brain. The low level of enzyme recovered from the brain suggests that modification of rc6S will be necessary to achieve sufficient enzyme uptake into the CNS for effective therapy of MPS IIID.