The Effects of Magnetic Resonance Imaging on Implantable Pulse Generators

The effects of magnetic resonance imaging were assessed on four dual chamber and two single chamber pulse generators. The tests were performed with a resistive, water-cooled magnet operating at 0.15 T. The 6.4-MHz radiofrequency (RF) field was operated at a maximum power of 1,000 watts with a period adjusted from 130 to 500 ms. Reed switch closure occurred in all six pulse generators tested when placed near the entrance of the magnetic resonance imaging scanner, and the generators reverted to asynchronous operation unless programmed to the "magnet off" mode. None of the pulse generators exhibited any alterations in programmed parameters or in the ability to be reprogrammed after RF pulsing. When the RF field was turned on, there was no change in the asynchronous paced cycle length in four pulse generators; however, during RF scanning there was rapid cardiac stimulation at the RF pulse period in one single chamber and one dual chamber pulse generator.     

Influence of Mobile Magnetic Resonance Imaging on Implanted Pacemakers

KISHI, R., et al.: Influence of Mobile Magnetic Resonance Imaging on Implanted Pacemakers. Purpose: Mobile magnetic resonance imaging (MRI) systems will be widely used in Japan. When traveling, mobile MRI generate alternating electromagnetic waves which may cause electromagnetic interference (EMI). This study was designed to determine whether this may influence the function of implanted pacemakers (PM). Methods and Results: The influence of the static magnetic fields was tested in the first method using a PM-human model (Phantom). Magnetic force was simultaneously measured. The PM was switched to the magnet mode within 90 cm from the vehicle, where the magnetic force was = 2 mT. In the second method, six phantoms were placed on the side of the road, facing in three different directions in X-Y-Z axis orientations, at 1.3 m and 2.0 m above the ground. The mobile MRI passed by at a distance of 1 m from the phantoms at the speed of 20 or 40 km/h. In these experiments, magnet mode switch of the PM was observed for 2 seconds when the vehicle passed close to the phantoms, though no electrical noise was recorded. Conclusion: Mobile MRI vehicles can switch a PM to magnet mode when the distance between patient and vehicle is <90 cm, regardless of whether the vehicle is moving or at a stop. Patients with implanted PM should not approach within <1 m of a mobile MRI. No other EMI-induced PM dysfunction was detected. (PACE 2003; 26[Pt. II]:527–529)     

Frequency of Magnetic Resonance Imaging Abnormalities in Patients With Migraine

Background.-The frequency of magnetic resonance imaging (MRI) abnormalities in patients with migraine has been reported at 12% to 46%. We examined a series of patients to determine the frequency of MRI abnormalities, and any relationship of frequency with patient age, sex, migraine type, duration of symptoms, and other medical conditions.
Methods.-Magnetic resonance imaging findings were reviewed retrospectively with respect to presence of focal white matter hyperintensities in 185 consecutive patients. Patients had been diagnosed with migraine by a neurologist. All images had been interpreted by a neuroradiologist. Clinical information was obtained by chart review.
Results.-Sixteen percent had focal white matter abnormalities. Among patients less than 50 years old, and without other medical problems such as hypertension, atherosclerotic heart disease, diabetes mellitus, autoimmune disorder or demyelinating disease, only 6% had white matter abnormalities. Increased frequency of white matter abnormalities was associated with age and medical risk factors, but not with sex, migraine subtype, or duration of migraine symptoms.
Conclusion.-The observed frequency of MRI abnormalities in our series is lower than has been previously reported. In many cases, these abnormalities may be unrelated to migraine. When such changes are discovered in a patient with migraine, other etiologies should be considered.     

Effects of Nuclear Magnetic Resonance Imaging on Cardiac Pacemakers

Patients with cardiac pacemakers are currently restricted from nuclear magnetic resonance imaging (MRI), The aim of the study was to analyze the influence of MBI on new generation pacemakers. Tests were performed using a phantom model with seven dual chamber and two single chamber systems in a 0.5 Tesla MRI scanner. Monitoring by telemetry and oscillography were used during the standard clinical scan sequences as well as a pacemaker inquiry after each sequence. Spin echo, gradient echo, and fast field echo sequences were performed with the following stimulation modes: VVI, VVIR, VOO, DDD, DDDR, and DOO. On entering the static magnetic field, the reed switch was activated followed by asynchronous stimulation. The subsequent scan showed no influence on the stimulation function nor on the pacemaker program. Event counter function remained intact. Pacemakers with automatic mode switching to demand pacing or programmed inactivotion of the reed switch were triggered in the dual chamber mode and were inhibited in the one chamber mode during the scan. Alterations of pacemaker program or rapid pacing were not observed. MRI scan could induce voltage as high as intracardiac signals, but the stimulation threshold of the heart was not reached. Thus, pacemakers should be programmed in the asynchronous mode during scan to avoid inhibition and trigger mechanism .     

Ectopy in Patients with Permanent Pacemakers and Implantable Cardioverter-Defibrillators Undergoing an MRI Scan

Background: Recent series suggest that magnetic resonance imaging (MRI) scanning can be performed safely in select patients with pacemakers or implantable cardioverter-defibrillators (ICDs). Limited data have been reported on ectopy during MRI scans in patients with pacemakers or ICDs. This study evaluated increased ectopy observed in patients with permanent pacemakers or ICDs undergoing MRI scanning of any landmark without peak specific absorption rate (SAR) limit.
Methods: Fifty-two patients with a total of 119 leads underwent a total of 59 MRI scans of any landmark using usual protocols with standard peak SAR settings for the scan. No patient was pacemaker dependent. All devices were programmed to single-chamber demand mode (VVI) or dual-chamber demand mode (DDI) with a lower rate of 40 bpm. Both telemetry and pulse oximetry plethysmographic waveform were observed continuously throughout the scans for ectopy.
Results: Increased ectopy was observed during seven scans. The ectopy in four scans was ventricular and had fixed coupling intervals of 1,500 and 3,000, and was likely due to device noise rejection behavior. The etiology of ectopy observed during the other three scans could not be determined. Ectopy could not be predicted by peak SAR, scan time duration, or landmark. No significant changes in pacing thresholds were seen postscan.
Conclusions: The current series suggests that a minority of patients with implanted pacemakers may have MRI-related ectopy. A significant proportion of this ectopy may arise from normal device behavior within the MRI environment.     

A New System for Follow-Up Patients with Permanent Pacemakers

BROFFONI, T., ET AL.: A New System for Follow-Up Patients with Permanent Pacemakers. The use of a new computerized system for coordinating technical and clinical data and especially for filing the parameters found during out-patient checkups enables us to rationally carry out follow-up of approximately 900 patients with pacemakers in our electrostimulation laboratory without wasting time or data. The system is composed of a personal Olivetti M240 computer, with a 20 Bbyte and 640 Kram hard disk, an analog-digital interface and a personalized data base for coordinating and filing the parameters found. The type of pacemaker implanted (monocameral, dual chamber or rate responsive) is of no consequence to the system that is based on the acquisition of the surface electrocardiogram. A comparison of the filed data on printouts or graphs allows us to note every type of misfunction or anomaly in the stimulation system in real time.     

心脏磁共振压缩感知电影序列的临床应用初探

目的 通过比较心脏磁共振（CMR）压缩感知序列（CS）与常规（CM）序列图像，观察CS序列的临床应用价值。方法 68例患者接受CM序列和CS序列CMR。分别记录2个序列的扫描时间，分析2个序列采集图像的质量、左心室心肌厚度、左心室心功能指标。结果 共纳入62例患者，CS序列平均扫描时间为（19.00±1.20）s，较CM序列缩短约82.66%。CS序列与CM序列图像质量差异无统计学意义（Z=-1.24，P>0.05）。2组图像测量左心室心肌厚度差异无统计学意义（P均>0.05）。分析左心室心功能结果显示，以CS序列图像（81.41 g/m²）测量的左心室舒张末心肌质量指数略小于CM序列图像（81.83 g/m²，P<0.05），2组其余心功能指标差异均无统计学意义。结论 采用CS序列采集的图像质量与CM序列无明显差异，可准确分析心功能，并大幅缩短检查时间，有望在CMR中替代CM序列。     

阿尔茨海默病与血管性痴呆的磁共振成像和脑电图特征比较

目的比较阿尔茨海默病(AD)与血管性痴呆(VD)头颅磁共振成像(MRI)和脑电图特征。方法观察39 例AD患者、56例VD患者的头颅MRI和脑电图资料。MRI比较大脑萎缩、海马萎缩、脑白质疏松症的比例;脑电图比较轻度异常和中重度异常的比例,进行功率谱分析。结果与VD患者相比,AD患者大脑萎缩、海马萎缩的发生率较高,脑白质疏松症发生率较低。AD患者脑电图中重度异常的较多,(θ+δ)/(α+β)比值增高(P<0.05)。结论单纯大脑萎缩而缺乏脑白质疏松症和缺血灶的痴呆患者应高度怀疑AD,脑电图出现中重度异常则进一步支持AD的诊断。     

高分辨磁共振成像用于阿尔茨海默病嗅球体积测量

  目的  评价阿尔茨海默病(Alzheimer disease, AD)患者嗅球体积变化。  方法  对14例AD患者及25名正常老年志愿者行高分辨嗅球磁共振成像(magnetic resonance imaging, MRI), 测量嗅球体积。  结果  AD患者较大侧嗅球体积为(32.2±7.7)mm³, 小于正常老年志愿者的(40.6±6.6)mm³(P=0.002)。AD患者嗅球体积与简易精神状态检查量表(mini-mental state examination, MMSE)评分无明显相关性(P=0.205)。  结论  AD患者嗅球体积减小, 符合神经病理学表现。MRI可以发现AD患者嗅球体积改变, 可能为AD诊断提供帮助。     

Magnetic Resonance Imaging in Migraine and Tension-Type Headache

Cerebral magnetic resonance imaging was performed on 63 patients with chronic primary headache (28 with migraine with and without aura, 35 with tension-type headache). Fifty-four headache-free individuals of the same age range were used as controls. The headache sufferers showed an incidence of focal white matter abnormalities on T2-weighted magnetic resonance imaging significantly higher than the age-matched control group (33.3% vs 7.4%). The incidence of white matter abnormalities did not correlate with age (except for patients older than 60 years), sex, headache history, headache status, or ergotamine consumption. Migraine (with and without aura) and tension-type headache patients had similar prevalence of white matter abnormalities (32.1% vs 34.3%). The lesions were predominantly distributed in the frontal region, independent of the side of usual aura or headache. Our findings indicate that both migraine and tension-type headache may be associated with early pathologic changes in the brain and may share, at least in part, common pathogenic pathways.     

腹壁子宫内膜异位症的磁共振成像表现

  目的  探讨腹壁子宫内膜异位症的磁共振成像(magnetic resonance imaging, MRI)表现特点。  方法  回顾性分析北京协和医院2008年1月至2013年1月经手术病理证实且行MRI检查的7例腹壁子宫内膜异位症患者的临床资料和MRI检查结果。  结果  7例腹壁子宫内膜异位症患者中5例单发, 2例多发; 7例患者共发现病灶10处, 7处病灶位于左侧, 2处位于正中, 1处位于右侧; 5处位于皮下及筋膜、未侵及腹壁肌层, 4处侵及腹壁肌层, 1处累及皮下、筋膜及腹壁肌层; 2处病灶与盆腔内部脏器粘连。10处病灶中, 9处病灶呈实性, T1WI及T2WI上以等信号或稍高信号为主; 1处病灶呈囊性, T1WI呈高信号, T2WI可见"阴影"现象。7例患者有5例合并子宫疾病。  结论  对于腹壁子宫内膜异位症, MRI不但能准确定位, 还能显示病变范围, 是术前检查及术后随访的重要方法。     

Effects of Extracorporeal Shock Wave Lithotripsy on Cardiac Pacemakers and its Safety in Patients with Implanted Cardiac Pacemakers

Ejects of extracorporeal shockwave lithotripsy (ESWL) were studied on 15 pacemakers (standard single chamber n = 5, dual chamber n = 6, rate responsive single chamber [Activitrax] n = 4). In-vitro testing involved suspending the pacemakers in a bath of degassified, deionized water firmly taped to a platform at the point of maximal pressure, i.e., second focal point (F2), where they received pressure shocks (x?= 1300) from the HM3 Dornier lithotriptor. The pacemakers, programmed to their most sensitive setting, were continuously pacing at nominal outputs (atria) and ventricular pacing in the DDD mode). All units were assessed by a pacing system analyzer before and after the study, then underwent destructive analysis. During standard single chamber pacing (VVI) the pacing stimulus triggered ESWL. For dual chamber devices, ESWL was triggered by the atrial paced event which induced inhibition of the ventricular output in two pacemaker. This was eliminated by reprogramming to a less sensitive setting. The pacemaker can, hermetic seal and internal circuitry were undamaged in all units. Two rate responsive single chamber pacemakers had their activity sensing piezoelectric elements shattered when placed at F2. Two other units placed 5 cm from F2 were stimulated to their maximum upper programmed pacing rate with ESWL therapy, but were otherwise unaffected. Subsequent to this study, six patients with pacemakers programmed to the VVI (five), DDD (one) modes implanted in the thorax underwent successful ESWL without pacemaker or arrhythmic event. Conclusions: (A) It is generally safe for patients implanted with standard single chamber devices in a ventricular application to undergo ESWL without modifying the pacing/sensing parameters. (B) Patients implanted with dual chamber devices who pace in the atrium should be reprogrammed to the VVI mode during ESWL. (C) Patients with piezoelectric activity sensing rate responsive single chamber pacemakers should have this feature programmed off during ESWL and, if implanted in the abdomen, probably should not undergo ESWL.     

痉挛型脑性瘫痪MRI研究

目的探讨颅脑MRI与脑瘫类型、患儿胎龄之间的关系。方法回顾性分析224例痉挛型脑瘫患儿的MRI检查和临床资料。结果224例患儿痉挛型偏瘫27例、双瘫149例、四肢瘫48例；MRI异常201例（89.7%），其中偏瘫、双瘫、四肢瘫的异常率分别为100%、87.2%和91.7%。痉挛型双瘫以脑室周围白质软化（PVL）最常见，发生率79.2%，其他类型脑损伤少见。痉挛型四肢瘫脑损伤多种多样，以PVL、足月儿类型脑损伤、先天发育畸形为主要表现，发生率分别为45.8%、20.8%和18.8%。足月儿痉挛型偏瘫以半侧损伤为主，临床表现为一侧肢体运动障碍，上肢重，下肢轻；未成熟儿痉挛型偏瘫表现为单侧或双侧PVL，临床表现为下肢重、上肢轻的偏瘫。152例PVL患儿中，发生于未成熟儿108例（71.1%）、足月儿44例（28.9%）。足月儿类型脑损伤22例，发生于足月儿20例（90.9%）。未成熟儿脑损伤类型主要为PVL，主要见于未成熟儿脑瘫，也可发生于足月儿脑瘫。足月儿类型脑损伤主要见于足月儿脑瘫，未成熟儿少见。结论颅脑MRI表现与脑瘫的类型、出生胎龄密切相关。     

磁共振成像在喉癌诊断中的应用价值

目的：探讨磁共振成像（MRI）在喉癌诊断中的应用价值。方法回顾性分析26例喉癌患者的MRI表现。结果26例喉癌中声门型l5例（57.7％）,声门上型7例（26.9％）,跨声门型4例（15.4％）,无声门下型。MRI表现为声带局部侵润、增厚,喉内软组织肿块、贯穿声门及周围组织浸润,颈部淋巴结转移。结论 MRI检查在诊断喉癌过程中能清晰准确并直观的反应癌肿侵犯的范围与邻近扩散情况,对于喉癌的早期诊断、分期及治疗具有重要意义。     

Magnetic Resonance Imaging and Signal-Averaged Electrocardiography in Patients with Repetitive Monomorphic Ventricular Tachycardia and Otherwise Normal Electrocardiogram

Early or localized forms of arrhythmogenic right ventricular dysplasia (ARVD) have been proposed as the arrhythmogenic substrate of repetitive monomorphic ventricular tachycardia (RMVT) originating in the right ventricular outflow tract in patients without any underlying cardiac abnormality on clinical examination and echocardiography. To further examine this hypothesis, magnetic resonance imaging (MRI) and signal-averaged electrocardiography (SAECG) were performed on 23 patients with RMVT and normal 12-lead standard ECG of conducted sinus beats. MRI was performed using ECG-gated turbo spin-echo images of the heart in order to detect signs of early or localized forms of ARVD, such as localized wall thickness reductions, signal intensity increase indicating adipose tissue infiltrates, and regional bulgings or aneurysms. MRI was normal in 22 (96%) of 23 study patients. In the remaining patient (4%), MRI demonstrated signal intensity increase in the intraventricular septum but not in the right ventricular outflow tract. Time-domain analysis of the SAECG was normal in 21 (91 %) of 23 patients and revealed ventricular late potentials in 2 study patients (9%). Frequency-domain analysis of the SAECG was normal in 22 (96%) of 23 patients and revealed ventricular late potentials in one study patient (4 %). We conclude that normal MRI findings of the heart and absence of ventricular late potentials in the SAECC in most patients with RMVT and otherwise normal ECG do not support the hypothesis that early or localized forms of ARVD create the arrhythmogenic substrate in the majority of these patients.     

Rapid Ventricular Pacing in a Pacemaker Patient Undergoing Magnetic Resonance Imaging

Magnetic resonance imaging (MRI) generates potent electromagnetic forces in the form of a static, gradient, or pulsed radiofrequency magnetic field that can result in pacemaker malfunction. This report documents a case of rapid cardiac pacing during MRI in a patient with a dual chamber pacemaker. Although the mechanism of rapid cardiac pacing is unclear, it was directly related to radiofrequency pulsing. We postulated that the lead acts as an antenna for radiofrequency energy that interacts with the pacemaker's output circuit, thus, causing cardiac pacing at a cycle length representing a multiple of the repetition time; or perhaps rapid pacing is related to induced currents generated between the MRI unit and the pacing lead.     

脑静脉血栓形成的临床与MRI表现

【目的】探讨脑静脉血栓形成(CVT)的临床与磁共振成像(MRI)特征。【方法】收集42例脑静脉血栓形成患者资料,详细分析其临床表现和MRI特征。【结果】90.5%的病人有头痛、呕吐等颅高压表现,50%的病人伴有局灶神经功能缺损如肢体无力、癫痫发作、视力下降等,21.4%的病人有精神异常,38.1%的病人仅表现为颅内压增高;MRI和磁共振静脉成像(MRV)能直接显示脑静脉闭塞及其血栓栓子。【结论】MRI和MRV对脑静脉血栓形成诊断起着重要作用。