2016年 · 第50卷第02期

progressive multifocal leukoencephalopathy (PML) is a fatal demyelinating lesion of the central nervous system caused by oligodendrocytes infected by John Cunningham (JC) virus^[1]。 PML by Astrom et al.^[2]First reported in 1958, it is a common complication in patients with advanced human immunodeficiency virus (HIV), with an incidence rate of up to 7%^[3]。 The clinical manifestations are characterized by multiple neurological defects, and the neurological function deteriorates rapidly. Very few PML can also be seen in patients with hematological malignancies, organ transplants and autoimmune deficiencies. PML is characterized by typical imaging and progressive white matter lesions. The diagnosis can be confirmed by combining clinical history and laboratory examination. The authors retrospectively analyzed the MRI findings of 7 patients with clinically proven PML, aiming to improve the understanding of this disease.

heterotaxy syndrome refers to the dislocation of the viscera and atrium, which is different from complete visceral inversion and transposition^[1]。 Visceral ectopic syndrome is often associated with complex congenital cardiac malformations, and the prognosis is poor. Prenatal diagnosis is crucial. Prenatal ultrasound plays an important role in the diagnosis of visceral ectopic syndrome^[2]However, it is sometimes affected by factors such as obesity of pregnant women, gestational age and fetal position, and occasionally it is restricted when showing visceral ectopic syndrome. MRI has a large visual field, high resolution of soft tissue, and is not easily affected by the above factors. It can clearly show fetal visceral ectopic syndrome, especially extracardiac structures. However, there are few reports on the diagnosis of fetal visceral ectopic syndrome by MRI at home and abroad. The author retrospectively analyzed 6 children with visceral ectopic syndrome diagnosed by prenatal MRI, and compared the autopsy results after induction of labor to explore the diagnostic value of MRI in fetuses with visceral ectopic syndrome.

Epidural meningioma and hypertrophic spinal pachymeningitis (HSP) are dura-related diseases. Their common feature is that the dura thickened to varying degrees, resulting in spinal canal stenosis, which leads to symptoms related to spinal cord or nerve root compression, and clinical diagnosis is difficult. The clinical management of the two is different: epidural meningioma is a tumor that requires surgical intervention, while HSP is classified as an IgG4-related disease^[1]Conservative treatment can be carried out, so accurate diagnosis is of great clinical significance. MRI has high soft tissue resolution and has advantages in showing dural-related lesions inside and outside the spinal canal, so it plays an important role in the diagnosis and differential diagnosis of these lesions. At the same time, CT can provide relevant supplementary information. The author made a comparative analysis of the imaging manifestations of the two diseases, aiming at improving the accuracy of diagnosis.

abdominal aortic aneurysm (AAA) is a serious life-threatening disease caused by abnormal expansion of the abdominal aorta. 1991 Parodi et al^[1]DSA-guided endovascular aneurysm repair (EVAR) has gradually become an important method for the treatment of subrenal AAA after endovascular stent implantation for the first time^[2]。 DSA technology is an indispensable technical means in EVAR. The interpretation of DSA images not only affects the success of stent implantation, but also plays a crucial role in the evaluation of postoperative efficacy. At present, clinicians' interpretation of DSA images obtained during surgery still remains on the analysis of pure gray-scale images. However, first of all, the gray-scale image can only show the morphological changes before and after stent implantation, and cannot quantitatively analyze the recovery of blood supply from the function; Secondly, there are many images in DSA movie files, so it is time-consuming to select appropriate images for judgment. In this study, the author uses pseudo-color coding technique to quantitatively analyze the perfusion of blood flow by performing maximum intensity projection (MIP) on the time axis and pseudo-color coding on the arrival time of contrast agent. This technique has been well used in the field of neuroimaging^[3]。 It has the advantage that it can provide intuitive vascular morphological information and quantitative hemodynamic parameters at the same time. The author used this technique in patients undergoing endovascular AAA repair to qualitatively and quantitatively analyze the iliac artery blood flow before and after stent placement, which is summarized as follows.

MRI has advantages in the diagnosis of maxillofacial diseases in nasopharynx, oropharynx, larynx and other parts, especially nasopharyngeal carcinoma. The precise radiotherapy of nasopharyngeal carcinoma requires MRI localization, and the scan range should also include the root of the neck^[1]。 Because of the large auxiliary equipment for positioning with membranes, scanning with neck coils cannot be performed. Although radiotherapy positioning images of the nasopharynx and upper neck can be obtained that meet clinical requirements by improving the sequence and using other coils (body coils, flexible coils, spinal coils) instead of head and neck coils. However, due to the particularity of anatomy, tissue composition and imaging characteristics of the neck root, the local magnetic field is not uniform, the resonance frequency changes, and the fat inhibition fails^[2]。 In addition, because there is a large amount of air in the alveoli and the neck and shoulder surfaces, the magnetic susceptibility of the air and soft tissue interface in this area is very different, and obvious magnetic susceptibility artifacts are easy to appear^[3]。 Therefore, plain scan of neck root fat suppresses T₂WI and enhanced fat inhibition T₁WI sometimes shows dissatisfaction, especially in thin patients, which are more prone to obvious chemical shift artifacts and magnetic susceptibility artifacts, and the fat inhibition effect is also unstable. The key technique of neck root examination in patients with nasopharyngeal carcinoma is to suppress fat signal to the maximum extent, eliminate or reduce various artifacts, and improve the signal-to-noise ratio of neck root image. The author used a self-made MRI shim assist device to scan patients with nasopharyngeal carcinoma radiotherapy localization with severe artifacts and poor fat inhibition after scanning with conventional methods, and achieved good image quality, which is reported below.

The patient was a 20-year-old male. He was transferred to our hospital on February 27, 2015 due to a fracture of his right upper arm for 7 days due to a car accident. Physical examination showed fracture of proximal right humerus with good external fixation with plaster. Outer courtyard DR (Figure 1) and CT showed fracture of right humerus and possible cyst at the proximal end of right humerus. The patient was obese and had a history of fatty liver and diabetes. Two years ago, the patient had undergone transnasal endoscopy combined with nasal lateral resection of skull base tumor resection + nasal sinus tumor resection under nasal endoscopy + nasal sinus surgery under left nasal endoscopy. The pathological findings of postoperative lesions were sand tumor-like ossifying fibroma.

A 21-year-old woman suffered from discomfort in her right pharynx for half a year, accompanied by foreign body sensation, local swelling and pain. The local anti-inflammatory treatment according to "wisdom tooth pericoronitis" was ineffective, and the local swelling was aggravated and difficulty in opening her mouth occurred for half a month. She had no hissing, cough, sore throat, blood in sputum and difficulty in breathing. Clinical specialist examination: A tumor was seen on the right upper palate, which was hard to touch, without fluctuation and inactivity. The transverse diameter was about 7 cm, extending outward to the right mandibular angle. The surface mucosa and skin color were normal, and there was no congestion, redness, swelling and ulcer.

The patient was a 35-year-old female. Seven months ago, B-ultrasound examination in another hospital revealed a space-occupying lesion of the liver, and MRI examination revealed a cystic-solid space-occupying lesion of the right liver with a diameter of about 14 cm (details unknown). More than 10 days ago, the patient underwent PET-CT examination in another hospital, which showed that there was a huge cystic-solid mass in the right lobe of the liver, which was considered as a benign neoplastic lesion, and no lesions were found in other parts. Since the onset of the disease, the patient has no obvious discomfort symptoms and no obvious change in body mass. Physical examination: Blood pressure was 160/100 mmHg (1 mmHg =0.133 kPa), and there were no obvious positive signs. Laboratory tests: Tumor markers were all in the normal range.

The patient was a 58-year-old female. Admitted to hospital for 3 years due to recurrent episodes of middle and upper abdominal pain. In 2011, due to abdominal discomfort, pancreatic space-occupying lesions were found by MRI, and conservative treatment was performed (specificity unknown). No previous history of uterine fibroids or gastrointestinal tumors. Physical examination: emaciation, anemic appearance. Laboratory tests: Hemoglobin 50 g/L (normal reference value 110~150 g/L), alpha-fetoprotein, carcinoembryonic antigen, sugar chain antigen 19-9, cancer antigen 125, total bilirubin, etc. were not abnormal.

The patient was a 23-year-old male. Intermittent stool with blood for more than 3 months. Anal diagnosis: 3 cm into the right wall of the rectum can be palpable with external pressure type hard mass, 5 cm ×5 cm, the mucosa is smooth, and the finger cuff is not stained with blood. Colonoscopy: 1 obvious extraintestinal compression was seen 3 cm from the anus. There were no abnormalities in the digestive tract tumor markers.

MRI has become an indispensable imaging method in clinical diagnosis and research. However, many types of high-intensity noise generated during MRI scanning will have a series of adverse effects on subjects and operators who have been in the scanning room for a long time, such as anxiety, language communication disorders, tinnitus, dizziness and other symptoms. In more severe cases, it may lead to temporary or permanent hearing threshold changes or even deafness^[1]。 Based on this, the author summarizes the characteristics and mechanism of noise generated by MRI system, the influence of noise on hearing, and summarizes the research progress of noise reduction technology.