基于LF-NMR及MRI 的2种速生材干燥过程中水分分布状态研究

为了解太阳能干燥过程中速生材内部水分状态及迁移规律,采用低场核磁共振及核磁共振成像检测桉、杨木干燥过程中水分分布、含量变化及迁移过程,借助扫描电镜在微观层面进行分析。结果表明：核磁共振信号强度与称重法所测含水率相关性系数高达0.99以上,因此低场核磁共振可准确测定木材中的水分含量;桉木和杨木饱水试样的核磁共振信号中均存在3种峰,桉木弛豫时间分别为1.32、32.75、403.70 ms,杨木为2.66、32.75、352.12 ms,对应着结合水及两种状态的自由水;随着干燥进行,不同状态水分的横向弛豫时间逐渐减小,木材对水分的束缚增加。当桉木含水率为27.28%,杨木含水率为35.71%左右时,水分散失转为以结合水为主。通过核磁共振成像中氢质子密度的不同可对水分含量进行区分,进而可观测干燥过程中木材内部水分移动状态。因此,通过低场核磁共振及核磁共振成像可研究速生材干燥过程中的内部水分状态及分布。     

MAGNETIC RESONANCE IMAGING OF THE PRESUMED NORMAL CANINE ADRENAL GLANDS

Forty-three dogs without evidence of endocrine disease that underwent spinal or abdominal magnetic resonance imaging (MRI) for clinical reasons were studied. Because the procedures were not optimized for inclusion of the adrenal glands, they were not always visible in all planes. Eighty-five of the 86 adrenal glands were seen and only the left gland in a 6-month-old Irish wolfhound could not be found. The right adrenal gland lay cranial to the left in all of the animals in which both glands were seen. The best landmarks for localization of the glands were vascular; both adrenal glands were always cranial to the ipsilateral renal vessels and in the region of the celiac and cranial mesenteric arteries. Various measurements were made on all the available scan planes. In some dogs the whole adrenal gland was difficult to visualize clearly, and this hindered the measuring process, especially when the right adrenal gland was in close contact with the caudal vena cava. The adrenal glands were mainly linear in shape but also had a variable degree of modification of their poles, especially the cranial pole of the right adrenal gland, which tended to be consistently wider and to present different shapes (rounded, arrowhead, inverted P, hook-shaped, triangular, or dome-shaped). Two main patterns of signal intensity were seen on fast spin echo (FSE) sequences (T2-weighted, T1-weighted, and T1-weighted after administration of a paramagnetic contrast medium): homogeneous and hypointense to surroundings or a corticomedullary type pattern with a hyperintense central area surrounded by a hypointense rim of tissue. The outline of the left adrenal gland was always very clear. The clarity of outline of the right adrenal gland was more variable, especially if it was in contact with the liver or the caudal vena cava. It was felt that the amount of retroperitoneal fat was not as important as stated in the human literature for visualization of the adrenal glands and that with an appropriate selection of scan planes and pulse sequences good assessment of the adrenal glands can be performed with MRI in canine patients.     

Three‐dimensional T1‐weighted gradient echo is a suitable alternative to two‐dimensional T1‐weighted spin echo for imaging the canine brain

Volumetric imaging (VOL), a three‐dimensional magnetic resonance imaging (MRI) technique, has been described in the literature for evaluation of the human brain. It offers several advantages over conventional two‐dimensional (2D) spin echo (SE), allowing rapid, whole‐brain, isotropic imaging with submillimeter voxels. This retrospective, observational study compares the use of 2D T1‐weighted SE (T1W SE), with T1W VOL, for the evaluation of dogs with clinical signs of intracranial disease. Brain MRI images from 160 dogs who had T1W SE and T1W VOL sequences acquired pre‐ and postcontrast, were reviewed for presence and characteristics of intracranial lesions. Twenty‐nine of 160 patients were found to have intracranial lesions, all visible on both sequences. Significantly better grey‐white matter (GWM) differentiation was identified with T1W VOL (P < .001), with fair agreement between the two sequences (weighted κ = 0.35). Excluding a mild reduction in lesion intensity in three dogs precontrast on the T1W VOL images compared to T1W SE, and meningeal enhancement noted on the T1W VOL images in one dog, not identified on T1W SE, there was otherwise complete agreement between the two sequences. The T1W VOL sequence provided equivalent lesion evaluation and significantly improved GWM differentiation. Images acquired were of comparable diagnostic quality to those produced using a conventional T1W SE technique, for assessment of lesion appearance, number, location, mass effect, and postcontrast enhancement. T1W VOL, therefore, provides a suitable alternative T1W sequence for canine brain evaluation and can facilitate a reduction in total image acquisition time.     

Magnetic resonance imaging of feline hippocampal necrosis

The clinical, neuropathologic, and magnetic resonance (MR) imaging features in four cats with necrosis of the hippocampus and piriform lobe are described. All cats had acute generalized seizures and behavioral changes including aggression, salivation, polyphagia, and disorientation. Routine hematologic, serum chemistry, and cerebrospinal fluid analyses were normal. MR imaging abnormalities were restricted to the area of the hippocampus and piriform lobe. The lesions were T2-hyperintense, T1-hypointense, and were characterized by various degrees of contrast enhancement. Lesions were consistent with necrotizing encephalitis. Two cats were euthanized and underwent postmortem examination within a week after MR imaging due to the lack of response to antiepileptic drug therapy and progressive neuropathy. The remaining two cats lived for about four months and were then euthanized because of persistent behavioral and neurologic signs; only one of these cats underwent postmortem examination with histopathologic examination. Histopathological findings were typical of severe, diffuse, bilateral symmetric necrosis, and degeneration of neurons in the hippocampus and piriform lobe, but an etiologic agent was not apparent. This apparently unique feline syndrome, now reported in Switzerland and Italy, has no known cause at this time.     

Magnetic resonance imaging‐guided injection of platelet‐rich plasma for treatment of an insertional core lesion of the deep digital flexor tendon within the foot of a horse

Definitive diagnosis of a deep digital flexor tendon insertional lesion within the right fore foot was made by magnetic resonance imaging (MRI) examination and the lesion subsequently treated by injection with platelet‐rich plasma. MRI was used to guide positioning of the needle to achieve highly accurate injection. The volume injected was found to approximate the calculated lesion volume. On the basis of experience with this case, MRI‐guided injection of insertional deep digital flexor tendon lesions of the foot of horses under general anaesthesia is practicable. This technique is likely to be more accurate than the other techniques described (computed tomography, ultrasonography) and carries no risk of exposure to radiation (radiography).     

Two‐Year Follow‐Up Magnetic Resonance Imaging and Spectroscopy Findings and Cerebrospinal Fluid Analysis of a Dog with Sandhoff's Disease

A 13‐month‐old female Toy Poodle was presented for progressive ataxia and intention tremors of head movement. The diagnosis of Sandhoff's disease (GM2 gangliosidosis) was confirmed by deficient β‐N‐acetylhexosaminidase A and B activity in circulating leukocytes and identification of the homozygous mutation (HEXB: c.283delG). White matter in the cerebrum and cerebellum was hyperintense on T2‐weighted and fluid‐attenuated inversion recovery magnetic resonance images. Over the next 2 years, the white matter lesions expanded, and bilateral lesions appeared in the cerebellum and thalamus, associated with clinical deterioration. Magnetic resonance spectroscopy showed progressive decrease in brain N‐acetylaspartate, and glycine‐myo‐inositol and lactate‐alanine were increased in the terminal clinical stage. The concentrations of myelin basic protein and neuron specific enolase in cerebrospinal fluid were persistently increased. Imaging and spectroscopic appearance correlated with histopathological findings of severe myelin loss in cerebral and cerebellar white matter and destruction of the majority of cerebral and cerebellar neurons.     

IMAGING DIAGNOSIS—MAGNETIC RESONANCE IMAGING OF A NEURONAL HETEROTOPIA IN THE BRAIN OF A CAT

A domestic shorthair kitten was presented for evaluation and further treatment of seizures. Magnetic resonance imaging of the brain revealed a large multilobulated mass in the third ventricle extending into the right lateral ventricle with secondary obstructive hydrocephalus. The mass was homogeneously isointense to gray matter on T2W, T2‐FLAIR, T2^*W, T1W, and ADC images, and hyperintense on DW‐EPI. There was no appreciable contrast enhancement. Seizures were managed medically and with subsequent ventriculoperitoneal shunt placement. Clinical status later deteriorated and the cat was euthanized. Histopathology confirmed that the mass was the result of neuronal heterotopia. To the authors’ knowledge this is the first report of neuronal heterotopia in a cat.