Techniques, terminology, and indications for MRI in pregnancy

Magnetic Resonance Imaging with Active Implantable Hearing Devices: Reports from the Daily Radiological Routine in an Outpatient MR Center

PURPOSE

For people with hearing implants (HI), magnetic resonance imaging (MRI) still presents some difficulties due to the built-in magnet. Radiologists often have concerns regarding complications associated with HIs. The aim of this study was to record the experiences of HI users during and after MRI examinations.

METHOD

A survey including 15 questions regarding MRI specifics, namely changes in hearing ability, hearing/sound impressions, pain, uncomfortable feelings, etc., were mailed to our patients.

RESULTS

Overall, 79 patients with HI had a total of 159 MR examinations in our institute. A total of 45 HI recipients reported back: 35% stated that they had been rejected by an MRI Institute because of their HI. Their feelings/impression ratings during the measurements were not present and therefore were not rated for the majority (49%), 42% of the HI users rated the pain with 0 (no pain), 2% with 1 (very light pain), 4% with 5 (acceptable pain), and 2% rated the pain with 7, which is between acceptable and strong pain. One examination resulted in a dislocation of the magnet of a cochlear implant (CI 512 Cochlear Limited). No adverse events were reported for MED-EL HI users in the survey (none of the contacted AB users answered the questionnaire). The reported mean daily wearing time was 11.6 ± 4.6 h per day for 6.3 ± 1.7 days per week.

CONCLUSIONS

Based on these results and our experience we conclude that MRI examinations with HI are safe given that the measurements are performed according to the safety policies and procedures released by the manufacturers.

Comparison of artefact reduction possibilities with the new active transcutaneous bone conduction implant (Bonebridge)

OBJECTIVE

This study aimed to evaluate the possibilities of artefact reduction using different anatomical implant positions with the Bonebridge bone-conduction hearing implant 602 for a patient with an acoustic neuroma requiring regular diagnostic magnetic resonance imaging of the tumour position.

METHOD

Three implant positions and magnetic resonance imaging examinations with and without customised sequences for metal artefact suppression were investigated. The diagnostic usefulness was rated by a radiologist (qualitative evaluation), and the relation between the area of artefact and the total head area was calculated (quantitative evaluation).

RESULTS

Following the qualitative analysis, the radiologist rated the superior to middle fossa implant placement significantly better for diagnostic purposes, which is in agreement with the calculated artefact ratio (p < 0.0001). The customised slice-encoding metal artifact correction view-angle tilting metal artifact reduction technique sequences significantly decreased the relative artefact area between 5.13 per cent and 25.02 per cent. The smallest mean artefact diameter was found for the superior to middle fossa position with 6.80 ± 1.30 cm (range: 5.42-9.74 cm; reduction of 18.65 per cent).

CONCLUSION

The application of artefact reduction sequencing and special anatomical implant positioning allows regular magnetic resonance imaging in patients with the bone-conduction hearing implant 602 without sacrificing diagnostic imaging quality for tumour diagnosis.

Incidental maternal findings on fetal MRI

AIM

To evaluate the type and frequency of maternal findings incidentally identified during fetal magnetic resonance imaging (MRI).

MATERIALS AND METHODS

A retrospective single-centre study was undertaken which included all consecutive fetal MRI studies performed between July 2017 and May 2021 at a tertiary institution. Two fellowship-trained radiologists reviewed the studies independently to determine the type and frequency of incidental maternal findings of both no clinical significance (requiring no further follow-up) and of clinical significance (requiring further follow-up, work-up, and/or management). Differences in acquisition were resolved by two-reader consensus. Non-diagnostic MRI examinations or abdominal MRI examinations indicated for maternal complications were excluded from review.

RESULTS

A total of 455 consecutive fetal MRI examinations performed in 429 women were included. Mean age was 30 years (SD 5.5 years). At least one incidental maternal finding was identified in 58% (265/455) of studies. Umbilical hernias (35%), maternal hydronephrosis (19%), and maternal hydro-ureter (15%) were the most common. Only two studies (0.5%) showed clinically significant incidental maternal findings (pancreatic pseudocyst and ovarian cyst).

CONCLUSIONS

Incidental maternal findings are common on fetal MRI but rarely require further follow-up, work-up, and/or management.

Kidney morphology in pregnancy using T2-weighted MRI

AIM

To report the morphology of maternal kidneys captured on fetal magnetic resonance imaging (MRI) including kidney length, volume, renal pelvis diameter, and corticomedullary differentiation in pregnancy.

MATERIALS AND METHODS

A retrospective study of maternal kidney morphology captured incidentally on fetal MRI. Women without chronic kidney disease, with a complete view of both kidneys and a singleton pregnancy were included. Kidney length, maximal renal pelvis diameter, kidney volume, and corticomedullary differentiation ratio were measured independently in duplicate. Associations with maternal and pregnancy variables were explored using linear regression.

RESULTS

MRI images from 42 women were performed at 22-32 weeks' gestation. Serum creatinine concentrations are not checked routinely during pregnancy and were available for 15 (36%) women, with a median creatinine of 57 μmol/l (IQR: 50-63 μmol/l). Mean interpolar lengths were 10.9 and 10.4 cm for the left and right kidneys and varied with height. Mean maximal renal pelvis diameters were 9 mm and 12 mm, with upper reference intervals of 17 and 25 mm for the left and right kidneys, respectively. Renal volume in pregnancy was within the non-pregnant reference interval and varied with height and gestation.

CONCLUSIONS

Maternal kidney length and volume in pregnancy are within the normal reference intervals for non-pregnant women. Renal pelvis diameter in pregnancy measured using MRI is substantially higher than described previously by ultrasound, with implications for routine reporting.

MRI in pregnancy: Indications and practical considerations

There is a constantly evolving knowledgebase regarding the safety of MRI in pregnant patients, as well as the safety of gadolinium administration, given potential fetal risks. This review provides an overview of national and international recommendations for patient screening and safety by trimester, evaluates the most recent literature regarding administration of gadolinium in pregnant patients, and discusses technical requirements when imaging pregnant patients. A protocol for imaging pregnant patients is provided, and multiple common indications for MRI in pregnancy are discussed. Level of Evidence 5. Technical Efficacy Stage 5. J. Magn. Reson. Imaging 2019;49:621-631.

A survey of pediatric diagnostic radiologists in North America: current practices in fetal magnetic resonance imaging

BACKGROUND

Fetal magnetic resonance imaging (MRI) is an imaging examination in evolution. Rapid developments over recent decades have led to better image quality, an increased number of examinations and greater impact on patient care.

OBJECTIVE

To gather data regarding current practices among established programs in North America and provide information to radiologists interested in implementing or growing a fetal MRI service.

MATERIALS AND METHODS

An electronic survey containing 15 questions relevant to the use of fetal MRI was submitted to pediatric radiologists and neuroradiologists. Items regarded scheduling and reporting logistics, magnet strength, patient positioning and patient preparation. Answers and comments were collected, and descriptive statistics were summarized.

RESULTS

One hundred and six survey responses were evaluated. Of the survey responses, 62/106 (58.5%) allow fetal MR scheduling any time during the day and 72/105 (68.6%) exclusively use 1.5-T strength platforms for fetal MRI, while only 7/105 (6.7%) use exclusively 3 T. Patient positioning is variable: supine, 40/106 (37.8%); left lateral decubitus, 22/106 (20.8%), and, patient's choice, 43/106 (40.6%). Of the centers responding, 51/104 (49.0%) require no particular fasting instructions, while 20/104 (19.2%) request the patient avoid caffeine before the scanning.

CONCLUSION

Logistical trends in performing fetal MRI may supplement the American College of Radiology's published technical standards and offer guidance to radiologists new to the field.

Real-time ultrasound-MRI fusion image virtual navigation for locating intraspinal tumour in a pregnant woman

BACKGROUND

Standard fluoroscopic guidance (C-arm fluoroscopy) has been routinely used for intraoperative localization of spinal level for surgical removal of intraspinal tumour, while it is not suitable for selected patients, e.g. pregnant women, who need to avoid radiation exposure. Fusion imaging of real-time ultrasound (US) and magnetic resonance imaging (MRI) is a radiation-free technique which has been reported to have good localization accuracy in managing several conditions.

CLINICAL PRESENTATION

A 37-year-old pregnant patient, presented with a progressively aggravating lower back pain for 20 days and was incapable of lying supine with lower extremities swelling for 1 week, was referred to our hospital in her 18th week of gestation. Lumbar MRI identified an L1 level intraspinal lesion, and surgery was planned. To avoid the ionizing radiation generated by fluoroscopy, volume navigation technique (VNT) based fusion imaging of US and MRI was used to localize the intraspinal lesion, which was removed entirely via minimally invasive interlaminar approach. Pathological examination confirmed the diagnosis of ependymoma of the conus medullaris. Her symptoms were largely relieved after the operation, and a healthy baby was delivered at the 40th week of pregnancy.

CONCLUSION

We presented the first case of using VNT based fusion imaging of real-time US/MRI to guide the surgical resection of an intraspinal tumour. Future study with larger patient number is needed to validate this technique as an alternative to fluoroscopy in patients who need to avoid radiation exposure.

Highlights on MRI of the fetal body

Fetal MRI is a level III diagnostic tool performed subsequently a level II prenatal ultrasound (US), in cases of inconclusive ultrasonographic diagnosis or when a further investigation is required to confirm or improve the diagnosis, to plan an appropriate pregnancy management. Fetal MRI plays an increasingly important role in the prenatal diagnosis of fetal neck, chest and abdominal malformations, even if its role has been amply demonstrated, especially, in the field of fetal CNS anomalies. Due to its multiparametricity and multiplanarity, MRI provides a detailed evaluation of the whole fetal respiratory, gastrointestinal and genitourinary systems, especially on T2-weighted (W) images, with a good tissue contrast resolution. In the evaluation of the digestive tract, T1-W sequences are very important in relation to the typical hyperintensity of the large intestine, due to the presence of meconium. The objective of this review is to focus on the application of fetal MRI in neck, chest and abdominal diseases.

Fetal MRI of the central nervous system: State-of-the-art

Prenatal ultrasonographic (US) examination is considered as the first tool in the assessment of fetal abnormalities. However, several large-scale studies point out that some malformations, in particular central nervous system (CNS) anomalies, are not well characterized through US. Therefore, the actual malformation severity is not always related to prenatal ultrasound (US) findings. Over the past 20 years, ultrafast Magnetic Resonance Imaging (MRI) has progressively increased as a prenatal 3rd level diagnostic technique with a good sensitivity, particularly for the study of fetal CNS malformations. In fact, CNS anomalies are the most common clinical indications for fetal MRI, representing about 80% of the total examinations. This review covers the recent literature on fetal brain MRI, with emphasis on techniques, safety and indications.

Numerical assessment of the reduction of specific absorption rate by adding high dielectric materials for fetus MRI at 3 T

The specific absorption rate (SAR) is an important issue to be considered in fetus MRI at 3 T due to the high radiofrequency energy deposited inside the body of pregnant woman. The high dielectric material (HDM) has shown its potential for enhancing B1 field and reducing SAR in MRI. The aim of this study is to assess the feasibility of SAR reduction by adding an HDM to the fetus MRI. The feasibility of SAR reduction is numerically assessed in this study, using a birdcage coil in transmission loaded with an electromagnetic pregnant woman model in the SEMCAD-EM solver. The HDMs with different geometric arrangements and dielectric constants are manually optimized. The B1+ ${B_1}^ + $ homogeneity is also considered while calculating the optimized fetus 10 g local SAR among different strategies in the application of HDM. The optimum maximum fetus 10 g local SAR was obtained as 2.25 W/kg, by using two conformal pads placed left and right with the dielectric constant to be 400, reduced by 24.75% compared to that without the HDM. It indicated that the SAR can be significantly reduced with strategic placement of the HDM and the use of HDM may provide a simple, effective and low-cost method for reducing the SAR for the fetus MRI at 3 T.

Fetal magnetic resonance imaging and ultrasound

Magnetic resonance imaging (MRI) has been increasingly adopted in obstetrics practice in the past three decades. MRI aids prenatal ultrasound and improves diagnostic accuracy for selected maternal and fetal conditions. However, it should be considered only when high-quality ultrasound cannot provide certain information that affects the counseling, prenatal intervention, pregnancy course, and delivery plan. Major indications of fetal MRI include, but are not restricted to, morbidly adherent placenta, selected cases of fetal brain anomalies, thoracic lesions (especially in severe congenital diaphragmatic hernia), and soft tissue tumors at head and neck regions of the fetus. For fetal anatomy assessment, a 1.5-Tesla machine with a fast T2-weighted single-shot technique is recommended for image requisition of common fetal abnormalities. Individual judgment needs to be applied when considering usage of a 3-Tesla machine. Gadolinium MRI contrast is not recommended during pregnancy. MRI should be avoided in the first half of pregnancy due to small fetal structures and motion artifacts. Assessment of fetal cerebral cortex can be achieved with MRI in the third trimester. MRI is a viable research tool for noninvasive interrogation of the fetus and the placenta.

The Zika virus and pregnancy: evidence, management, and prevention

OBJECTIVE

To comprehensively review the available evidence and existing consensus reports and guidelines regarding the pregnancy and reproductive implications of the mosquito-transmitted Zika virus (ZIKV) infection. A primary focus was to provide pertinent information to aid clinicians in the management of pregnancies at risk for, exposed to, or with confirmed ZIKV infection.

METHOD

An extensive literature review was performed using Pubmed. Practice guidelines and consensus reports were accessed from international, national, and professional organizations' websites. The clinical articles for ZIKV infection testing varied from case reports to small epidemiologic studies.

RESULTS

A ZIKV epidemic has been declared in several countries in the Americas. Fifty-two travel-associated ZIKV infection cases have been reported throughout the USA (as of February 10, 2016). The consequences of congenital fetal/newborn ZIKV infection could potentially have devastating consequences including miscarriage, fetal death, and major anomalies such as microcephaly, brain and brain-stem defects, and long-term neurologic sequelae. While not definitive, current evidence suggests the existence of nonvector-borne transmission through sexual activity with an infected male partner. For women at risk for sexual transmission, condom use is advised, especially during pregnancy.

CONCLUSION

While ZIKV infection appears to be a mild disease in the general population the potential consequences to the fetus and newborn could be profound. Management guidelines are currently evolving and will be significantly impacted as new evidence develops. It is therefore imperative that obstetric health-care providers keep abreast of this rapidly evolving information landscape that has so far characterized this outbreak.

[New aspects from legislation, guidelines and safety standards for MRI]

Many aspects of magnetic resonance (MR) operation are not directly regulated by law but in standards, guidelines and the operating instructions of the MR scanner. The mandatory contents of the operating instructions are regulated in a central standard of the International Electrotechnical Commission (IEC) 60601-2-33. In this standard, the application of static magnetic fields in MRI up to 8 Tesla (T) in the clinical routine (first level controlled mode) has recently been approved. Furthermore, the equally necessary CE certification of ultra-high field scanners (7-8 T) in Europe is expected for future devices. The existing installations will not be automatically certified but will retain their experimental status. The current extension of IEC 60601-2-33 introduces a new add-on option, the so-called fixed parameter option (FPO). This option might also be switched on in addition to the established operating modes and defines a fixed device constellation and certain parameters of the energy output of MR scanners designed to simplify the testing of patients with implants in the future.The employment of pregnant workers in an MRI environment is still not generally regulated in Europe. In parts of Germany and Austria pregnant and lactating employees were prohibited from working in the MR control zone (0.5 mT) in 2014. This is based on the mostly unresolved question of the applicability of limits for employees (exposure of extremities to static magnetic fields up to 8 T allowed) or the thresholds for the general population (maximum 400 mT). According to the European Society of Urogenital Radiology (ESUR), the discarding of breast milk after i.v. administration of gadolinium-based contrast agents in the case of a breastfeeding woman is only recommended when using contrast agents in the nephrogenic systemic fibrosis (NSF) high-risk category.

Perinatal Thoracic Mass Lesions: Pre- and Postnatal Imaging

Chest masses present a common problem in the perinatal period. Advances in prenatal ultrasound, supplemented by fetal magnetic resonance imaging, now allow early detection and detailed characterization of many thoracic lesions in utero. As such, in asymptomatic infants, assessment with postnatal computed tomography or magnetic resonance imaging can often be delayed for several months until the time at which surgery is being contemplated. Bronchopulmonary malformations comprise most of the thoracic masses encountered in clinical practice. However, a variety of other pathologies can mimic their appearances or produce similar effects such as hypoplasia of a lung or both lungs. Understanding of the key differentiating clinical and imaging features can assist in optimizing prognostication and timely management.

MRI evaluation and safety in the developing brain

Magnetic resonance imaging (MRI) evaluation of the developing brain has dramatically increased over the last decade. Faster acquisitions and the development of advanced MRI sequences, such as magnetic resonance spectroscopy (MRS), diffusion tensor imaging (DTI), perfusion imaging, functional MR imaging (fMRI), and susceptibility-weighted imaging (SWI), as well as the use of higher magnetic field strengths has made MRI an invaluable tool for detailed evaluation of the developing brain. This article will provide an overview of the use and challenges associated with 1.5-T and 3-T static magnetic fields for evaluation of the developing brain. This review will also summarize the advantages, clinical challenges, and safety concerns specifically related to MRI in the fetus and newborn, including the implications of increased magnetic field strength, logistics related to transporting and monitoring of neonates during scanning, and sedation considerations, and a discussion of current technologies such as MRI conditional neonatal incubators and dedicated small-foot print neonatal intensive care unit (NICU) scanners.