An improved passive shimming approach to design correction iron pieces for high field MRI.

This paper proposes a new passive shimming method to design correction iron pieces for compensating field impurities generated by the main magnets of high field magnetic resonance imaging (MRI) for human body imaging. First, the relationship formula of a magnetic dipole to any field point in space is established. Then, a sensitivity matrix in the form of spherical harmonic expansions can be set up based on the contribution of each shim piece to each field point. Next, an optimization procedure of linear programming is applied to determine the location and thickness of the ferromagnetic shim pieces. This is different from the previous methods that consider that all magnetic moments for each magnetized iron piece are located only at its central position, which may cause some intrinsic errors. This method takes the shim piece's volume into account and gives more accurate results in a sensitivity matrix by means of integration in the azimuthal and axial directions while the radial (thickness) direction remains constant. Finally, a case study combining the analytical method and a 3D finite element analysis simulation demonstrates that the new approach provides better results in terms of homogeneity. The method presented can also be used to design passive shims for various practical MRI applications.

2-[(2-Meth-oxy-benzyl-idene)amino]-phenol.

In the title compound, C(14)H(13)NO(2), the azomethine double bond adopts an E conformation and the benzene rings form a dihedral angle of 77.70 (7)°. In the crystal, mol-ecules are linked by O-H⋯N and C-H⋯O hydrogen bonds and arranged in a zigzag fashion, forming infinite chains parallel to the c axis, resulting in a graph-set R(2) (2)(9) motif.

Noise characteristics of grass-trimming machine engines and their effect on operators.

Over the last few years, interaction of humans with noisy power-driven agricultural tools and its possible adverse after effects have been realized. Grass-trimmer engine is the primary source of noise and the use of motorized cutter, spinning at high speed, is the secondary source of noise to which operators are exposed. In the present study, investigation was carried out to determine the effect of two types of grass-trimming machine engines (SUM 328 SE and BG 328) noise on the operators in real working environment. It was found that BG-328 and SUM-328 SE produced high levels of noise, of the order of 100 and 105 dB(A), respectively, to which operators are exposed while working. It was also observed that situation aggravates when a number of operators simultaneously operate resulting in still higher levels of noise. Operators should be separated 15 meters from each other in order to avoid the combined level of noise exposure while working with these machines. It was found that SPL, of the grass-trimmer machine engines (BG-328 and SUM-328 SE), were higher than the limit of noise recommended by ISO, NIOSH, and OSHA for an 8-hour workday. Such a high level of noise exposure may cause physiological and psychological problems to the operators in long run.

Diastereotopy in some 3,4-dihydroisocoumarins--effect of changing the substituents on the chiral centre.

Diastereotopy has been investigated in eight different derivatives of 3,4-dihydroisocoumarins by changing the substituent on the pyran ring chiral centre, C-3. A diastereotopic NMR effect is observed for the prochiral methylene protons on the benzopyran ring and the effect is greatly influenced by the pi-electron system of the substituent. The effect is also observed for the substituents, however, the extent of diastereotopy depends upon their nature and the separation of methylene groups from the chiral centre.

Facial clefts in Saudi Arabia: an epidemiologic analysis in 179 patients.

One hundred and seventy-nine consecutive cases of facial clefts that were treated at the King Khalid University Hospital, in Riyadh, Saudi Arabia, were analyzed for an epidemiologic study. Isolated cleft lip was present in 38 percent, cleft of lip and palate in 37.4 percent, and cleft of the posterior palate in only 22.4 percent. There was a male preponderance in all types. In cases of cleft lip with or without cleft palate, the more commonly affected side was the left, followed by bilateral cases. Associated malformations were present in 13.4 percent. A positive family history was found in 26.8 percent of cases. A significant number of patients (7.8 percent) were first seen at more than 10 years of age. The incidence of facial clefts at this hospital was 0.3 per 1000 live births, computed over a period of 6 years. This incidence is significantly lower than that reported from European and Far Eastern countries.

Four years' experience of limb replantation in Saudi Arabia: a clinical review.

This is a review of 70 patients with traumatic limb and digit amputations treated at King Khalid University Hospital, Riyadh in Saudi Arabia from April 1984 to April 1988. Out of 70 cases 34 were not suitable for replantation. In the remaining 36 patients replantation or revascularization was attempted on 46 units. The data are discussed and compared with other published series. Our net survival rate was 67.4 per cent. The survival rate improved from 62.8 per cent in the first 2 years to 81.8 per cent in the subsequent 2 years. The average hospital stay (34 days) was much longer than that reported from developed countries. The increased emergency workload due to a high incidence of referral of unsuitable cases and the longer hospital stay should be taken into account while establishing a replant service in a developing country. Eighteen cases were followed up for more than 1 year; of these, 61 per cent had good (grade I or grade II) functional recovery. The survival rate and functional recovery improved with increased experience and this is a strong argument in favour of centralizing the replant services.