Pulse sequence optimization for MR imaging using a paramagnetic hepatobiliary contrast agent

Paramagnetic agents enhance contrast between tissues in magnetic resonance (MR) imaging by altering tissue relaxation times. The effect of these changes on MR image intensity depends in part on the choice of operator-controlled pulse sequence parameters. With the newly described paramagnetic hepatobiliary contrast agent, iron(III) ethylenebis-(2-hydroxyphenylglycine), Fe(EHPG)-, an in vivo experimental analysis of pulse sequence optimization was performed on the rat. We compared the enhancement of the liver divided by background noise, EL/N, of standard inversion-recovery (IR) and spin-echo (SE) T1-weighted pulse sequences and several pulse sequences theoretically predicted to have improved EL/N. Optimization of the echo time (TE = TEmin) gave a substantial (greater than 60%) increase in EL/N over the standard IR and SE pulse sequences. Images obtained with optimized repetition rate and inversion time gave only a slight additional improvement. Within the uncertainties of our relaxation measurements, the measured changes in EL/N with pulse sequence optimization corresponded well with theoretical predictions. With the experimental and theoretical data, the importance of using a short echo time to obtain maximal T1 contrast in contrast-enhanced MR imaging and the relative merits of optimized SE versus IR pulse sequences for contrast-enhanced MR imaging are discussed.     

Evolution in the management of Hirschsprung��s disease in the UK and Ireland: a national survey of practice revisited

INTRODUCTION

The management of Hirschsprung’s disease continues to evolve. This questionnaire survey aimed to determine current surgical management strategies for Hirschsprung’s disease in Britain.

SUBJECTS AND METHODS

The survey was sent electronically to all British paediatric surgeons. Initial questions explored individual experience and regional service provision. Additional questions, reserved for surgeons who perform definitive Hirschsprung’s disease surgery, addressed specific clinical scenarios.

RESULTS

Surveys were sent to 142 surgeons yielding 85 responses. After exclusions, 64 surveys from 21 centres were analysed. Forty-seven respondents worked in centres with designated ‘Hirschsprung’s disease surgeons’. Forty respondents perform definitive Hirschsprung’s disease surgery. In a well neonate with left-sided Hirschsprung’s disease, 34 of 40 surgeons favour primary pull-through following bowel decompression with rectal washouts; 35 of 40 surgeons aim to perform definitive surgery at less than 3 months of age, with 17 favouring laparoscopic-assisted Soave–Boley and 15 favouring an open Duhamel pull-through. Of the 40 surgeons, 36 use a staged approach to right-sided/total colonic Hirschsprung’s disease with 23 favouring a Duhamel or Long Duhamel pull-through.

CONCLUSIONS

The primary pull-through, using an open Duhamel or laparoscopic-assisted Soave–Boley technique, during the first 3 months of life, has become the operative strategy of choice in rectosigmoid Hirschsprung’s disease in Britain. Marked variation in practice remains for right-sided Hirschsprung’s disease.     

Pathophysiological mechanisms of dominant and recessive KVLQT1 K+ channel mutations found in inherited cardiac arrhythmias

The inherited long QT syndrome (LQTS), characterized by a prolonged QT interval in the electrocardiogram and cardiac arrhythmia, is caused by mutations in at least four different genes, three of which have been identified and encode cardiac ion channels. The most common form of LQTS is due to mutations in the potassium channel gene KVLQT1, but their effects on associated currents are still unknown. Different mutations in KVLQT1 cause the dominant Romano-Ward (RW) syndrome and the recessive Jervell and Lange-Nielsen (JLN) syndrome, which, in addition to cardiac abnormalities, includes congenital deafness. Co- expression of KvLQT1 with the IsK protein elicits slowly activating potassium currents resembling the cardiac Iks current. We now show that IsK not only changes the kinetics of KvLQT1 currents, but also its ion selectivity. Several mutations found in RW, including a novel mutation (D222N) in the putative channel pore, abolish channel activity and reduce the activity of wild-type KvLQT1 by a dominant-negative mechanism. By contrast, a JLN mutation truncating the carboxyterminus of the KvLQT1 channel protein abolishes channel function without having a dominant-negative effect. This fully explains the different patterns of inheritance. Further, we identified a novel splice variant of the KVLQT1 gene, but could not achieve functional expression of this nor of a previously described heart-specific isoform.      

低聚果糖口服补液盐的试制

目的：改良口服补液盐（ＯＲＳ）,使其具有微生态调节作用、并与肠道内渗透压相似。方法：将氯化钠２．６ｇ、氯化钾１．５ｇ、枸橼酸钠２．９ｇ、低聚果糖（ＦＯＳ）２０ｇ和葡萄糖１０ｇ等混合后低聚果糖口服液盐（ＦＯＳ－ＯＲＳ）。密封包装,使用时加开水１０００ｍｌ冲服。可采用高效液相色谱法测定ＦＯＳ的含量。结果：ＦＯＳ－ＯＲＳ为白色散剂,加水后为无色透明液体,味甜中微咸,其浓度（ｍｍｏｌ／Ｌ）为钠７５、钾２０     

Mutations in purine nucleoside phosphorylase deficiency

Purine nucleoside phosphorylase deficiency is an inherited disease of purine metabolism characterized clinically as combined immunodeficiency. The molecular defects have been published for 4 different alleles in 3 patients. We report four new mutations including two amino acid substitutions, A 174P and G190V, a single codon deletion, ΔI129, and a point mutation in intron 3 which leads to aberrant splicing and creation of a premature stop codon in exon 4 (286 -18G→A). Of the previously reported mutations, E89K was found in one additional patient, and R234P was found in 3 unrelated patients, making R234P the most common mutation reported to date in this disease. Hum Mutat 9:118–121, 1997. © 1997 Wiley-Liss, Inc.     

MR imaging of facial nerve enhancement in Bell palsy or after temporal bone surgery

The authors evaluated magnetic resonance (MR) images obtained with intravenously administered gadolinium in ten patients who had facial paralysis and no facial nerve tumor. In patients with either Bell palsy (four patients) or facial paralysis after temporal bone surgery (six patients), intratemporal facial nerve enhancement was seen. Facial nerve enhancement on MR images proved to be a nonspecific finding.     

Intracranial circulation: pulse-sequence considerations in three- dimensional (volume) MR angiography

The technique and feasibility of magnetic resonance (MR) angiography of intracranial vessels were studied in 35 healthy volunteers. Variations in image orientation, repetition time (TR), and flip angle were evaluated to determine their effects on flow-related enhancement. Gradient modifications--including echo time (TE), motion compensation, bandwidth, and field of view--were also studied in an effort to reduce motion-induced phase shifts. Results indicated that a FISP (fast imaging with steady precession) sequence with a TR of 50 msec, TE of 15 msec, velocity compensation in the read and section-select directions, acceleration compensation in the read direction, anisotropic volume, and a 1.25-mm partition thickness produced three-dimensional angiographic MR images that were accurate and reproducible in the depiction of the major intracranial vessels. Difficulties with field of view, persistent signal void secondary to higher-order motion, and spatial resolution remain major problems requiring additional study.