Early MR features of hypoxic-ischemic brain injury in neonates with periventricular densities on sonograms

BACKGROUND AND PURPOSE: In the early 1980s, diagnosing periventricular leukomalacia (PVL) in neonates by using cranial sonography was possible for the first time. Our purpose was to investigate the possibility of diagnosing PVL in the acute stage by using MR imaging. We evaluated early MR features of hypoxic-ischemic brain injury in neonates with periventricular densities (flares) on cranial sonograms to determine the added value of MR imaging over sonography alone for early diagnosis of brain damage. METHODS: In a prospective study, infants who showed flares and/or cysts on sonograms underwent MR imaging during the (sub)acute stage. RESULTS: Fifty infants were classified according to the highest sonographic grade up to the day of MR imaging: 23 infants had sonographic grade 1 (flares < 1 week), 15 had sonographic grade 2 (flares > or = 1 week), four had sonographic grade 3 (small localized cysts), and eight had sonographic grade 4 (extensive periventricular cysts); none had sonographic grade 5 (multicystic leukomalacia) on the day of MR imaging. Overall, the additional information provided by MR imaging (over sonography alone) consisted of the depiction of hemorrhagic lesions in 64% of the infants. Extent and severity of the hemorrhages varied from isolated punctate lesions to extensive hemorrhages throughout the white matter; the latter were followed by cystic degeneration at autopsy in two infants. In nine of the 12 infants with cystic PVL, MR images showed more numerous or more extensive cysts. In addition, in two infants, MR images showed cysts not present on sonograms. In 32% of the infants, MR imaging provided no additional information; in these children, all but one had flares on sonograms whereas MR images showed no abnormalities or a zone of mild periventricular signal change. CONCLUSION: MR imaging can depict the precise site and extent of hypoxic-ischemic brain injury at an earlier stage and allows a wider differentiation of lesions as compared with sonography alone. Hemorrhagic PVL is considered to be rare, but was present in 64% of our study population.     

ECG-synchronized cardiac MR imaging: method and evaluation

An electrocardiographic (ECG) sensing and gating device compatible with a 0.35-tesla (T) magnetic resonance (MR) imager has been developed and used to produce 802 MR images of the heart in 30 patients. The instrument consists of an isolated acquisition module, an electrically floating preamplifier, and a monitor gating module. Two spin-echo images were acquired for each of five, 0.7-cm thick, transaxial sections from the base to the apex of the heart during each ECG-synchronized imaging run. Image quality was assessed in a blind study by two investigators, on a scale from 0 to 3, as diagnostic [2-3] or nondiagnostic [0-1]. There was agreement in 91.4% of their assessments of diagnostic images (68.1% of the images studied). Resolution of heart anatomy on the MR images was adversely affected by prolonged spin-echo time delay, imaging in late diastole, image acquisition at the cardiac apex, irregular triggering, and artifacts. The synchronization of gradient pulses to the ECG at 0.35 T appears safe for patients, permits diagnostic resolution of images, allows image acquisition at distinct points during the cardiac cycle, and enables monitoring of patients during imaging.     

Intraoperative MR imaging guidance for intracranial neurosurgery: experience with the first 200 cases

PURPOSE: To review preliminary experience with an open-bore magnetic resonance (MR) imaging system for guidance in intracranial surgical procedures. MATERIALS AND METHODS: A vertically oriented, open-configuration 0.5-T MR imager was housed in a sterile procedure room. Receive and transmit surface coils were wrapped around the patient's head, and images were displayed on monitors mounted in the gap of the magnet and visible to surgeons. During 2 years, 200 intracranial procedures were performed. RESULTS: There were 111 craniotomies, 68 biopsies, 12 intracranial cyst evaluations, four subdural drainages, and five transsphenoidal pituitary resections performed with the intraoperative MR unit. In each case, the intraoperative MR system yielded satisfactory results by allowing the radiologist to guide surgeons toward lesions and to assist in treatment. In two patients, hyperacute hemorrhage was noted and removed. The duration of the procedure and the complication rate were similar to those of conventional surgery. CONCLUSION: Intraoperative MR imaging was successfully implemented for a variety of intracranial procedures and provided continuous visual feedback, which can be helpful in all stages of neurosurgical intervention without affecting the duration of the procedure or the incidence of complications. This system has potential advantages over conventional frame-based and frameless stereotactic procedures with respect to the safety and effectiveness of neurosurgical interventions.     

MR imaging and CT evaluation of congenital pulmonary vein abnormalities in neonates and infants

Magnetic resonance (MR) imaging and computed tomography (CT) are increasingly being used in diagnosis and follow-up of congenital pulmonary vein anomalies in neonates and infants. Such anomalies include total or partial anomalous pulmonary venous return, sinus venosus defect, malposition of the septum primum, cor triatriatum, pulmonary vein atresia or stenosis, and abnormal number or course of the pulmonary veins. MR imaging provides a wealth of anatomic and functional data that are valuable in case management and planning intervention. Gadolinium-enhanced MR angiography is the mainstay of anatomic evaluation. Ventricular volumetry with two-dimensional steady-state free-precession sequences and flow analysis with cine phase-contrast imaging provide physiologic information that may be used to calculate the degree of right heart enlargement and the shunt fraction, allowing the cardiologist to determine the functional importance of the lesion. CT provides superior spatial resolution and short imaging times but at the expense of exposure to ionizing radiation.     

PET/MR images acquired with a compact MR-compatible PET detector in a 7-T magnet

PURPOSE: To prospectively use compact avalanche photodiodes instead of photomultiplier tubes to integrate a positron emission tomographic (PET) detector and a 7-T magnetic resonance (MR) imager. MATERIALS AND METHODS: All animal experiments were performed in accordance with the University of Tübingen guidelines and the German law for the protection of animals. A compact lutetium oxyorthosilicate-avalanche photodiode PET detector was built and optimized to operate within a 7-T MR imager. The detector performance was investigated both outside and inside the magnet, and MR image quality was evaluated with and without the PET detector. Two PET detectors were set up opposite each other and operated in coincidence to acquire PET images in the step-and-shoot mode in a mouse head specimen after injection of fluorine 18 fluorodeoxyglucose. RESULTS: The performance of the PET detector when operated inside the magnet during MR image acquisition showed little degradation in energy resolution (increase from 14.6% to 15.9%). The PET detector did not influence MR imaging. The fused PET and MR images showed an anatomic match and no degradation of image quality. CONCLUSION: Simultaneous PET and MR imaging with a 7-T system was deemed feasible.     

Clinically relevant rat model for testing BOLD functional MR imaging techniques by using single-shot echo-planar imaging at 1.5 T

By using a 1.5-T whole-body magnetic resonance (MR) imager, a high-spatial-resolution single-shot echo-planar technique was developed to perform blood oxygen level dependent functional MR imaging of rat sensory cortex during forepaw stimulation. This technique produced cubic 1-mm(3) voxels. Signal-to-noise ratio was 140-160 (43-44 dB). Optimal effective echo time was 50 msec. This system should prove useful for developing new functional MR imaging techniques with rapid adaptation to human use.     

Simultaneous MR/PET imaging of the human brain: feasibility study

The purpose of this study was to apply a magnetic resonance (MR) imaging-compatible positron emission tomographic (PET) detector technology for simultaneous MR/PET imaging of the human brain and skull base. The PET detector ring consists of lutetium oxyorthosilicate (LSO) scintillation crystals in combination with avalanche photodiodes (APDs) mounted in a clinical 3-T MR imager with use of the birdcage transmit/receive head coil. Following phantom studies, two patients were simultaneously examined by using fluorine 18 fluorodeoxyglucose (FDG) PET and MR imaging and spectroscopy. MR/PET data enabled accurate coregistration of morphologic and multifunctional information. Simultaneous MR/PET imaging is feasible in humans, opening up new possibilities for the emerging field of molecular imaging.     

In vitro evaluation of platinum Guglielmi detachable coils at 3 T with a porcine model: safety issues and artifacts

PURPOSE: To evaluate safety-related issues and imaging artifacts of Guglielmi detachable coils in vitro with 3-T magnetic resonance (MR) imaging. MATERIALS AND METHODS: Two aneurysm models were constructed: one from porcine carotid artery and the other from a pharmaceutical capsule. Both were filled with Guglielmi detachable coils. The models were tested with a 3-T MR imager for heating, deflection, and imaging artifact. Testing for heating and deflection was performed (a) at static points both inside and outside the bore, (b) during movement into the imager, and (c) during clinical imaging sequences. RESULTS: No change in temperature was measured during movement into the imager bore or at different points within the bore. No differences in heating from radio-frequency energy were found between aneurysm models and controls. Similarly, no evidence of deflection of the coil mass (capsule model) was found. Minor susceptibility artifacts were found in the readout direction during gradient-echo sequences. Magnetic field mapping showed no induced field inhomogeneity. CONCLUSION: MR imaging at field strengths of 3 T in patients with aneurysms treated with Guglielmi detachable coils is safe. Imaging artifacts are likely to be minimal.     

A clinical, noninvasive, MR imaging-monitored ultrasound surgery method.

A noninvasive method of tissue ablation that is guided and monitored with magnetic resonance (MR) imaging has been developed. The method uses sharply focused ultrasound transducers of different focal lengths to induce a localized temperature elevation during a short exposure (1-20 seconds). A hydraulic, computer-controlled positioning device moves the transducer in an MR imager. The positioner is built into a standard cradle in the imager. The system includes cavitation detection and power monitoring circuitry for patient safety. The target volume is outlined with cross-sectional MR images obtained immediately before sonication. By means of the software, the focus is moved to ablate the volume defined with the images. The temperature elevation during the exposure is monitored by means of the proton resonance frequency shift with fast gradient-echo sequences, and the necrosed volume is demonstrated with T2-weighted fast spin-echo images. This method has been extensively tested in in vivo animal experiments and is now undergoing clinical trial.     

Value of fluid-attenuated inversion recovery sequences in early MRI of the brain in neonates with a perinatal hypoxic-ischemic encephalopathy

The aim of our study was to assess the usefulness of fluid-attenuated inversion recovery (FLAIR) sequences in comparison with conventional spin-echo and inversion MR imaging in neonates for evaluation of myelination and for detection of hypoxic-ischemic brain injury. We reviewed early MR scans of 18 neonates with suspected hypoxic-ischemic brain damage. Myelination could be evaluated with confidence using conventional MR imaging in all but 2 infants; however, the presence of myelin was very difficult to assess on FLAIR images. Overall, 53 lesions or groups of lesions were identified. The FLAIR technique was more sensitive in 11 of the lesions; especially (pre)cystic lesions could be identified much better and more cysts were found. Conventional MR imaging failed to identify 2 of the lesions and was more sensitive in 14 of the lesions; especially punctate hemorrhages and lesions in basal ganglia or thalami could be better determined. The FLAIR technique missed 3 of these lesions. In the remaining 28 lesions conventional MR and FLAIR images were equally diagnostic. The FLAIR technique and conventional MR imaging are complementary in detecting early sequelae of hypoxic-ischemic brain injury in neonates. The FLAIR technique is not suitable for assessing myelination of the neonatal brain; therefore, FLAIR cannot replace conventional MR imaging. Received: 11 January 2000; Revised: 10 April 2000; Accepted: 10 April 2000     

Image quality associated with the use of an MR-compatible incubator in neonatal neuroimaging

Objectives

MRI in the neonate poses significant challenges associated with patient transport and monitoring, and the potential for diminished image quality owing to patient motion. The objective of this study was to evaluate the usefulness of a dedicated MR-compatible incubator with integrated radiofrequency coils in improving image quality of MRI studies of the brain acquired in term and preterm neonates using standard MRI equipment.

Methods

Subjective and objective analyses of image quality of neonatal brain MR examinations were performed before and after the introduction of an MR-compatible incubator. For all studies, the signal-to-noise ratio (SNR) was calculated, image quality was graded (1–3) and each was assessed for image artefact (e.g. motion). Student''s t-test and the Mann–Whitney U-test were used to compare mean SNR values.

Results

39 patients were included [mean gestational age 39 weeks (range 30–42 weeks); mean postnatal age 13 days (range 1–56 days); mean weight 3.5 kg (range 1.4–4.5 kg)]. Following the introduction of the MR-compatible incubator, diagnostic quality scans increased from 50 to 89% and motion artefact decreased from 73 to 44% of studies. SNR did not increase initially, but, when using MR sequences and parameters specifically tailored for neonatal brain imaging, SNR increased from 70 to 213 (p=0.001).

Conclusion

Use of an MR-compatible incubator in neonatal neuroimaging provides a safe environment for MRI of the neonate and also facilitates patient monitoring and transport. When specifically tailored MR protocols are used, this results in improved image quality.MRI of the brain is an important clinical tool for the evaluation of neonates with encephalopathy, suspected brain injury or developmental brain anomalies. Specific MR techniques may also provide information on myelination, metabolism and functional capabilities of the neonatal brain [1-3].Neuroimaging in the neonate presents a number of challenges. Transporting the critically ill neonate to the MRI unit presents significant practical problems. These infants require a carefully controlled microenvironment with a need for thermoregulation and constant haemodynamic monitoring and may need ventilatory support [4]. Handling the infant immediately prior to image acquisition can cause distress, and resultant movement may produce non-diagnostic images due to motion artefact. Sedation of neonates and infants can be performed but is not without risk, and a sedated neonate requires continuous monitoring during the examination with MR-compatible pulse oximetry and electrocardiogram [5,6].MR-compatible neonatal incubators have been developed to provide a safe and efficient method of transporting neonates to the MR suite and to allow monitoring of the baby during the examination. Stabilisation of the neonatal head within the incubator and close attention to swaddling technique are necessary to reduce patient movement during image acquisition, thereby reducing the need for sedation. Many of these incubators are equipped with an integrated radiofrequency (RF) coil, specifically tailored to the size of the neonate, which should improve image quality by increasing the signal-to-noise ratio (SNR). Previous studies have shown promising results with regard to patient safety [7,8]. Currently, there is little information on how image quality from an integrated incubator–coil unit compares with standard MR equipment [8]. Maximising image quality can be achieved by using a closely fitting RF coil (a dedicated neonatal head coil or a knee coil) and by modifying MR sequences which need to be specifically tailored to the neonatal brain because of its higher water content [5].The aim of our study was to compare the imaging performance of an MR-compatible incubator with integrated RF coils with standard MRI equipment in both term and preterm neonates.     

Physiologic changes during high field strength MR imaging

High field strength MR imaging systems may require several kilowatts of RF power to obtain images. A fraction of this power is absorbed by the patient, and changes in body temperature have been measured in experimental animals. The purpose of this study was to quantify changes in body surface temperature and other physiologic parameters in humans during MR scanning at 1.5 T. Blood pressure, heart rate, respiration, and axillary temperature measurements were obtained on 27 normal volunteers. Measurements were made at RF power levels of 0, 0.2, and 0.8 W/kg, with the power sequence randomized. In 14 volunteers receiving lumbar scans, statistically significant increases in temperature were observed at RF power levels of 0.2 (+0.2 +/- 0.1 degree C) and 0.8 (+0.5 +/- 0.1 degree C) W/kg. No significant changes related to RF power were observed in blood pressure or respiratory rate. At the 0.8 W/kg level there was a slight increase in heart rate (3 +/- 1.3 beats per minute). In the 13 patients receiving head scans, physiologic changes were substantially smaller. The temperature increases and other physiologic changes observed during MR scanning with the 1.5 T imager at RF powers of 0.2 and 0.8 W/kg were small and of no clinical concern. Additional studies should be performed in patients with cardiac failure, vascular occulusion, and metallic implants or prostheses.     

Abnormalities of the neonatal brain: MR imaging. Part II. Hypoxic- ischemic brain injury

Eighty-five infants, 82 of whom were 29-44 weeks postconceptional age, were imaged with a 0.6-T magnet. Eight infants had cerebral infarction. In premature neonates with very water, low-intensity white matter on T1-weighted images, ultrasound was better than both computed tomography and magnetic resonance (MR) imaging in depicting parenchymal changes of infarction or edema. However, after 37 weeks gestation, MR imaging was superior. Cerebral atrophy, present in seven infants, was consistent with subarachnoid space widths of 7 mm or more, or subarachnoid space widths of 5-6 mm with ventricular/brain ratios of 0.36 or greater. Delayed myelination was seen in a total of 18 infants with histories of hypoxic-ischemic insult. MR imaging shows promise in the neonatal period. It facilitates recognition of infarcts in full-term infants and may be used to predict abnormal neurologic outcome in infants who have initial delayed myelination.     

Extracorporeal membrane oxygenation in infants: angiographic and parenchymal evaluation of the brain with MR imaging

The authors report their preliminary experience with intracranial three-dimensional Fourier transform magnetic resonance (MR) angiography and T2-weighted MR imaging of the brain parenchyma in 15 neonates less than 1 week old after extracorporeal membrane oxygenation (ECMO) with permanent ligation of the right common carotid artery and internal jugular vein, four 1-year-old infants after ECMO with carotid ligation, and four neonates less than 1 week old after ECMO with reanastomosis of the same artery. MR angiography was technically satisfactory in 20 of the 23 patients and documented patency of the right internal carotid artery proximal to the ophthalmic artery in nine of 16 patients with permanent carotid ligation and in all four patients with reanastomosis. This study suggests MR angiography is feasible in newborns and infants and that, in combination with parenchymal MR imaging, it provides a sensitive, noninvasive method to assess vessel patency and follow cerebrovascular and parenchymal changes in infants after ECMO.     

MR imaging of herpes simplex type 1 encephalitis in infants and young children: a separate pattern of findings

OBJECTIVE: We sought to identify the initial MR findings of herpes simplex encephalitis in infants and young children. CONCLUSION: MR imaging findings of herpes encephalitis in infants and young children appear to differ from those seen in neonates, older children, and adults. Appreciation of this MR imaging pattern coupled with a strong clinical suspicion of herpes helps to ensure the correct diagnosis is made.     

Cranial MR imaging with Gd-DTPA in neonates and young infants: preliminary experience

Gadopentetate dimeglumine (gadolinium diethylenetriaminepentaacetic acid [DTPA]) was prospectively administered to 15 consecutive neonates and young infants (less than 6 weeks old) referred for routine cranial magnetic resonance (MR) imaging. The goals of the study were (a) to provide preliminary safety and efficacy data concerning the use of this drug in neonates and (b) to determine whether the patterns and time course of normal contrast material enhancement were similar to those seen in older children and adults. Gd-DTPA-enhanced MR images revealed significant abnormalities not seen on the MR images obtained before administration of contrast material in four (27%) of 15 patients. The adult dose (0.1 mmol/kg) provided bright enhancement of normal intracranial structures. Because of significantly reduced glomerular filtration and renal clearance rates in newborns, vivid contrast enhancement of normal structures was seen to persist for several hours after injection. A prolonged window of time for imaging may therefore exist for neonates and young infants.     

Improved renal cortical SPECT of neonates and young infants using narrow imaging pallets.

OBJECTIVE: The widths of most commercially-made imaging pallets limit the resolution of 99mTc DMSA SPECT imaging in neonates and young infants. We constructed a pediatric imaging pallet for 99mTc DMSA SPECT of neonates and young infants designed to allow close apposition of the camera to these patients during the entire orbit. METHODS: We designed the imaging pallet to replace the standard removable pallet on the imaging stand of a commercial gamma camera. The device consisted of two parts: a steel bracket attached to the imaging stand and a polyvinyl chloride imaging pallet. The imaging pallet consisted of interchangeable 15.24-cm (6-in) or 20.32-cm (8-in) diameter, 6.35-mm (1/4-in) thick polyvinyl chloride plumbing pipes cut in half lengthwise. RESULTS: The pallets were mechanically stable with loads 3 times that expected in clinical practice. Attenuation was acceptable and comparable to commercial pallets. The hemicylindrical shape provided side support and reduced patient motion, as well as allowing closer apposition of the camera head to the patient. The quality of these 99mTc DMSA SPECT images compared favorably with those obtainable in older children and adults. Specifically, the renal cortices were well delineated from the collecting systems and anatomic detail of normal cortex could be readily distinguished from abnormal cortex. CONCLUSION: Custom pediatric imaging pallets optimized for use in neonates and small children can be constructed inexpensively. These pallets are easy to use and are stable. Use of these pallets can optimize 99mTc DMSA SPECT images of neonates and young infants.     

Gd-DTPA-polylysine—enhanced pulmonary time-of-flight MR angiography

The enhancing effect of gadolinium diethylenetriam-inepentaacetic acid (DTPA) polylysine (a macromolecular paramagnetic contrast agent) in time-of-flight magnetic resonance (MR) angiography of isolated perfused sheep lungs was studied. Unilateral lung damage was induced with hydrochloric acid in eight sheep. The heart and lungs were removed from the thoracic cavity, and after cannulation of the trachea and both ventricles, pulsatile perfusion and ventilation were initiated. The heart-lung preparations were placed in the head coil of a 1.5-T imager. Time-of-flight pulmonary MR angiography was performed during respiratory arrest, before and after administration of 0.02 mmol/kg Gd-DTPA-polylysine. On the postcontrast angiograms, the signal intensity increased by 120% in pulmonary arteries (P <.01). The contrast-to-noise ratio between pulmonary arteries and parenchyma increased significantly (P <.01). The number of visualized generations of pulmonary artery branches increased from four to six in normal lungs and from three to five in edematous lungs. Low-dose Gd-DTPA-polylysine significantly improves the conspicuity of the pulmonary vascular tree in time-of-flight pulmonary MR angiography.     

Imaging of congenital anomalies and variations of the caudal spine and back in neonates and small infants

Spinal dysraphisms are categorized in open dysraphisms with prominent abnormal nervous tissue above the skinlevel and closed dysraphisms with a skin covered malformation. Especially the occult dysraphisms are marked by suspect skin masses and other dermal anomalies. The purpose of this review is to demonstrate the indications and spectrum of spinal sonography in neonates and infants. In comparison typical dysraphisms are demonstrated in sonography and MR Imaging. We demonstrate the value of ultrasound in comparison to MRI and describe a usefull handling of the methods in neonates and infants. The differentiation between the potentially dangerous dimples associated with dermal sinus, which can lead to meningitis and the harmless coccygeal dimple in the cranial gluteal cleft is presented. An inconspicious examination does not need a further imaging, but suspicious results of sonography need an MR imaging dependent of clinical conditions. Neurologically conspicious infants need MR imaging completed by sonography. Great advantages of sonography are the real time examination and the potential to show oscillations of the conus, filum and cauda equina in M-mode-imaging.     

Human heart: tagging with MR imaging--a method for noninvasive assessment of myocardial motion

Specified regions of the myocardium can be labeled in magnetic resonance (MR) imaging to serve as markers during contraction. The technique is based on locally perturbing the magnetization of the myocardium with selective radio-frequency (RF) saturation of multiple, thin tag planes during diastole followed by conventional, orthogonal-plane imaging during systole. The technique was implemented on a 0.38-T imager and tested on phantoms and volunteers. In humans, tags could be seen 60-450 msec after RF saturation, thus permitting sampling of the entire contractile phase of the cardiac cycle. Tagged regions appear as hypointense stripes, and their patterns of displacement reflect intervening cardiac motion. In addition to simple translation and rotation, complex motions such as cardiac twist can be demonstrated. The effects of RF pulse angle, relaxation times, and heart rate on depiction of the tagged region are discussed.