Ultrafast Magnetic Resonance Imaging Research Articles

Ultrafast magnetic resonance imaging of omphalopagus conjoined twins

Conjoined twins are extremely rare congenital malformations. Omphalopagus twins are the second most common variety of conjoined twins and usually are joined at the umbilicus. Herein, we present ultrafast magnetic resonance imaging (MRI) feature of this rare anomaly at 24 weeks of gestation. Ultrafast MRI can provide additional information that may help ultrasonography for antenatal characterization of such anomalies.

Aggregated wavelet estimation and its application to ultra-fast fMRI

The methodology of aggregation of known nonparametric regression estimators into a single better estimator has received increasing attention in statistical literature. Traditional aggregation means that a linear or convex combination of several estimators is considered. Wavelet regression estimation, due to its multiresolution nature, presents another opportunity for aggregation – using different estimation procedures on different resolution scales. Such an opportunity becomes attractive if known wavelet estimators have desired complementary properties on different frequencies. The difficulty of such an aggregation is that the assignment of scales depends on an underlying regression function and regression errors. This paper proposes a data-driven aggregation of two wavelet estimators – SureBlock of Cai and Zhou [(2009), ‘A Data-driven Block Thresholding Approach to Wavelet Estimation’, Annals of Statistics, 37, 569–595] and Universal of Efromovich [(1999a,b), Nonparametric Curve Estimation: Methods, Theory and Applications, New York: Springer; ‘Quasi-linear Wavelet Estimation’, Journal of the American Statistical Association, 94, 189–204] – to achieve a better quality of estimation, better data-compression, and better visualisation of functions with different smoothness characteristics on low and high frequencies. The proposed estimator is motivated by an applied problem of denoising and compression of ultra-fast (UF) functional magnetic resonance imaging (fMRI) – the new magnetic resonance technology that screens the activity of brain voxels every 50 ms with the purpose of understanding human brain activity. The proposed aggregated wavelet estimator is supported by the asymptotic theory, tested via intensive numerical simulations and UF fMRI applications, and it is expected to be useful in similar applications.

Ultrafast MRI of the fetus: an increasingly important tool in prenatal diagnosis of congenital anomalies

Objective To demonstrate the additional utility of ultrafast magnetic resonance imaging (MRI) of the fetus in the evaluation of sonographically detected or equivocal fetal congenital anomalies. Material and Methods Twenty five pregnant women with ultrasound detected fetal congenital anomalies underwent ultrafast fetal MRI. Results MRI findings altered the diagnosis of two cases of giant arachnoid cyst and sizable interhemispheric cyst associated with agenesis of the corpus callosum. MRI added additional findings of occult spinal diastematomyelia in two out of four cases of Chiari/meningocele malformation. MRI revealed impaired sulcation and unilateral cleft palate in suspected case of Walker-Warburg syndrome. In the remaining 18 cases MRI confirmed the diagnosis of Meckel–Gruber syndrome in three cases, hydronephrosis in six cases, cerebral ventriculomegaly in five cases, isolated omphalocele in three cases and findings suggestive of aneuploidy in the last case. Conclusion Ultrasound is the screening method of choice for evaluation of the fetus. Ultrafast MRI is a complementary adjunctive modality with excellent tissue contrast that can image the fetus in multiple planes and add information in sonographically detected or equivocal congenital anomalies that may be significant to establish definitive accurate diagnosis and hence adequate management and counseling.

The role of ultrasound and antenatal single-shot fast spin-echo MRI in the evaluation of herniated bowel in case of first trimester ultrasound diagnosis of fetal gastroschisis

To report on a clinical antenatal management strategy based on integrating ultrasound (US) and magnetic resonance imaging (MRI) in the evaluation of herniated bowel following early prenatal diagnosis of gastroschisis. Antenatal US and ultrafast single-shot spin-echo (SSSE) MRI. Fetal gastroschisis was documented at 12 weeks at the time of first trimester screening for Down syndrome. Fetal karyotype was performed at 16 weeks and showed a 46,XY karyotype. Ultrasound scan at 20 weeks diagnosed gastroschisis as isolated finding. Follow-up scans were planned monthly, and antenatal ultrafast SSSE MRI was arranged at 35 weeks and demonstrated a right fetal abdominal wall defect measuring 2.4 mm on transverse diameter with an integrity of the intra-abdominal and extra-abdominal loops of small bowel. The colon was in situ as were the stomach, the liver, and the spleen. The choice of integrating both the diagnostic procedures has shown to be clinically useful in planning the timing of delivery (Cesarean section) and in turn has been associated with an easy surgical repair and to a favorable postnatal outcome. The result of amniocentesis was crucial for the parent's decision-making process whether to continuing with the pregnancy. Moreover, amniotic fluid α-fetoprotein levels may be used as an index of small bowel damage when loops of small bowel lied uncovered within the amniotic cavity.

Quantitative Ultra-Fast MRI of HPMC Swelling and Dissolution

For the first time quantitative Rapid Acquisition with Relaxation Enhancement (RARE) based ultra-fast two-dimensional magnetic resonance imaging has been used to follow the dissolution of hydroxypropylmethyl cellulose (HPMC) in water. Quantitative maps of absolute water concentration, spin-spin relaxation times and water self-diffusion coefficient are obtained at a spatial resolution of 469 microm in less than 3 min each. These maps allow the dynamic development of the medium release rate HPMC/water system to be followed. It is demonstrated that the evolution of the gel layer and, in particular, the gradient in water concentration across it, is significantly different when comparing the quantitative RARE sequence with a standard (nonquantitative) implementation of RARE. The total gel thickness in the axial direction grows faster than that in the radial direction and that the dry core initially expands anisotropically. Additionally, while HPMC absorbs a large amount of water during the dissolution process, the concentration gradient of water within the gel layer is relatively small. For the first time MRI evidence is presented for a transition swollen glassy layer which resides between the outer edge of the dry tablet core and the inner edge of the gel layer.

Cephalothoracopagus, janiceps, disymmetros, monoomphalian conjoined twins undiagnosed until early second trimester

Cephalothoracopagus is the less common type of conjoined twins (CTs) with an incidence estimated at one in three million births or one in 58 conjoined twins. Maternal gene Vg1, a member of the TGF-beta family of cell-signalling molecules which are implicated in dorsoanterior development, and specific actions of Hox and Pax genes that are implicated in very early embryogenesis may be identified as aetiologic factors. A prenatal diagnosis of cephalothoracopagus CTs diagnosed at 17 weeks in a woman undergoing amniocentesis for advanced maternal age is reported. Although first-trimester diagnosis of CTs is feasible and has been reported as early as 8 weeks's gestation, CTs may be misdiagnosed with monoamniotic twins, lymphangioma, teratoma, and/or neoplasm and may be undiagnosed until early second trimester. Three-dimensional and color Doppler ultrasound enabled precise prenatal visualization of the fusion site. Ultrafast MR imaging should be considered an adjunct to ultrasound for antenatal characterization of structural anomalies and for planning surgical separation in selected cases. Echocardiography is mandatory in all cases of CTs as congenital heart defects are seen in 20-30% and polyhydramnios in 50-75%. Neural tube and midline fusion defects, diaphragmatic hernia, and imperforate anus are the frequently associated abnormalities. Prognosis among survivors is usually poor (44% die in the neonatal period) and is dependent upon the type of conjunction, degree of involvement of the shared organs, and presence or absence of associated anomalies, with the worst prognosis in case of twins sharing liver and heart.

Appearances of diffuse excessive high signal intensity (DEHSI) on MR imaging following preterm birth

Diffuse damage to the periventricular white matter has recently been suggested to be a cause of the cognitive deficits seen following preterm birth. It is unclear whether this form of injury can be visualised on MR imaging, but one group has described diffuse excessive high signal intensity (DEHSI) as a possible form of diffuse white matter injury. This finding is dependent on window imaging and the subjective assessment of the reviewer, but little data have been published on the degree of subjectivity on its appearance among raters. To assess the subjectivity of DEHSI on conventional and ultrafast T2-weighted MR imaging following preterm birth. An observational study of 40 preterm infants who had MR imaging of the brain around term-equivalent age, including conventional fast spin-echo (FSE) and ultrafast single-shot fast spin-echo (SSFSE) T2-weighted sequences in the axial plane. Images were anonymised and scored twice by four observers for the presence of DEHSI. Inter- and intra-observer agreement were calculated. Sixty-five percent of conventional and 100% of the ultrafast images were of diagnostic quality. DEHSI was noted in between 0% and 69.2% of conventional images and 27.5-90% of the ultrafast images. Inter- and intra-observer agreement ranged from none to moderate. The visual appearances of DEHSI on conventional FSE and ultrafast SSFSE T2-W images are highly subjective, limiting its clinical application.

Improved B0 field map estimation for high field EPI

Echo planar imaging (EPI) is an ultrafast magnetic resonance imaging (MRI) technique that allows one to acquire a 2D image in about 100 ms. Unfortunately, the standard EPI images suffer from substantial geometric distortions, mainly originating from susceptibility differences in adjacent tissues. To reduce EPI distortions, correction methods based on a field map, which is a map of the off-resonance frequencies, have been developed. In this work, a nonlinear least squares estimator is used to optimize the estimation of the field map of the B(0) field. The model of the EPI and reference data includes parameters for the phase evolution, the complex magnitude, the relaxation of the MRI signal and the EPI-specific phase difference between odd and even echoes, and from these parameters, additional corrections might be computed. The reference data required to estimate the field map can be acquired with a modified EPI-sequence. The proposed method is tested on simulated as well as experimental data and proves to be significantly more robust against noise, compared to the previously suggested method.

Characterisation of pulsing flow in trickle-bed reactors using ultra-fast magnetic resonance imaging

Characterisation of pulsing flow in trickle-bed reactors using ultra-fast magnetic resonance imaging

Prenatal Diagnosis of Monosomy 17p (17p 13.3 → pter) Associated With Polyhydramnios, Intrauterine Growth Restriction, Ventriculomegaly, and Miller-Dieker Lissencephaly Syndrome in a Fetus

To present the prenatal magnetic resonance imaging (MRI) and ultrasound findings of Miller-Dieker lissencephaly syndrome (MDLS) associated with chromosome 17p13.3 deletion in a fetus. A 30-year-old, primigravid woman was referred to the hospital at 31 weeks' gestation because of intrauterine growth restriction (IUGR) and polyhydramnios detected by ultrasound. The pregnancy was uneventful until 31 weeks of gestation when IUGR and polyhydramnios were first noted. Level II ultrasound at 31 weeks' gestation showed fetal biometry equivalent to 27 weeks' gestation, an amniotic fluid index of 33.4 cm, ventriculomegaly, and abnormal sulcal development with absence of gyri and sulci, and a shallow Sylvian fissure. Other organs were unremarkable. Subsequent amniocentesis revealed a 46,XY,del(17)(p13.3) karyotype. Ultrafast fetal MRI performed at 34 weeks of gestation revealed agyria/pachygyria, a figure-eight appearance of the brain, a wide and shallow Sylvian fissure, enlarged subarachnoid space, ventriculomegaly, and polyhydramnios. At 35 weeks' gestation, a 1,346-g male baby was delivered with facial dysmorphism, characteristic of MDLS. Postnatal MRI confirmed the prenatal diagnosis. Polyhydramnios, IUGR and ventriculomegaly are important prenatal ultrasound markers of MDLS. Prenatal diagnosis of these markers should include a detailed investigation of cerebral sulci and fissures, and genetic analysis for MDLS. Fetal MRI is helpful for the diagnosis of lissencephaly.

Retrobulbar Optic Nerve Diameter Measured by High-Speed Magnetic Resonance Imaging as a Biomarker for Axonal Loss in Glaucomatous Optic Atrophy

To assess a novel magnetic resonance imaging (MRI) protocol for quantifying the optic nerve diameter (OND) as a measure of axonal loss in the optic nerve. Included in the study was one eye each from 47 subjects, of whom 9 had no eye disease, 16 had preperimetric glaucoma, 11 had a glaucomatous mean visual field defect of <10 dB and 11 of >10 dB. Each subject underwent automated perimetry, scanning laser polarimetry, optic coherence tomography, scanning laser tomography, and ultrafast high-resolution MRI at 3 T. OND was determined 5, 10, and 15 mm behind the eye with a half Fourier-acquired single-shot turbo spin-echo (HASTE)-sequence requiring 1.5 seconds of data acquisition time per slice and providing a spatial resolution of 0.11 mm. A multiple linear regression model was applied to determine correlations (r) among the different techniques. The correlation (r) was <0.37 for OND measurements taken 5 mm behind the eye. At 10 mm behind the eye, r increased to 0.57 and was statistically significant in four out six instances. In the orbital apex 15 mm behind the eye, r reached a maximum of 0.80 and was statistically significant in all instances. OND correlated best with the retinal nerve fiber layer thickness measured by optic coherence tomography. Retina- or optic nerve head-related surrogate markers for axonal content correlated closely with the OND, although only when it was measured in the orbital apex. High-resolution MRI using an ultrafast HASTE-sequence at 3 T proved useful for OND quantification and may be a valuable asset in future neuroprotection trials.

Dynamic MRI of the vocal cords using phased-array coils: A feasibility study

Objective:Endoscopy for evaluation of hoarseness is an invasive procedure and the result depends, to a large extent, on the patient's cooperation. Successful laryngoscopy can also be hampered by unfavourable anatomic conditions, a severely impaired general condition, or severe coagulopathy. We evaluated the feasibility of doing ultra-fast magnetic resonance imaging (MRI), using a recent dedicated coil design and a sequence with inherently high signal-to-noise ratios (SNR), for the detection of motility disorders of the vocal cords.Materials and Methods:Twelve consecutive patients (eight males and four females) in the age range of 24–80 years (mean age 60 years) with persistent hoarseness and presumed vocal cord palsy were included in this blinded prospective study. Two two-element phased-array carotid coils were used for signal reception. The first coronal real-time steady-state free precession (SSFP) sequence was performed during silence (i.e., with no vocal cord motion) and the second while phonating ‘heee.’ Qualitative MRI findings were compared with the results of the endoscopic examination.Results:The examination time for setup, patient instruction and positioning, localization scans, and real-time SSFP scans was less than 10 min. Seven patients with laryngoscopically-confirmed unilateral palsy of the vocal cord were correctly identified with MRI. The five remaining patients had hoarseness due to causes other than vocal cord palsy; they showed normal motion of the vocal cords on MRI and endoscopy.Conclusion:Compared to preceding studies, the image quality in this study is supported by excellent SNR (carotid phased-array coils and SSFP sequence with higher SNR if compared to a spoiled gradient-echo sequence or an EPI sequence). Further studies, with larger groups of patients, are necessary to show if this protocol can serve as an alternative to endoscopy in selected cases.

Molecular Magnetic Resonance Imaging of Myocardial Perfusion With EP-3600, a Collagen-Specific Contrast Agent

Cardiac magnetic resonance (MR) perfusion imaging during the first pass after intravenous administration of extracellular contrast agents is hampered by the spatial and temporal resolution achievable and by the artifacts seen in ultrafast MR imaging. Furthermore, time-consuming quantitative data analysis is often added. The use of molecular MR imaging with a target-specific contrast agent with perfusion-dependent binding to myocardium may enable prolonged visualization of perfusion defects and thus may help to overcome limitations of currently used first-pass extracellular MR imaging. EP-3600 is a new gadolinium-containing molecular contrast agent that binds reversibly to myocardial collagen. A significant but nonocclusive coronary artery stenosis was modeled in 7 domestic swine with an undersized MR-compatible balloon positioned in the left anterior descending artery as verified by x-ray angiography. Two animals died before contrast injection as a result of arrhythmias. In 5 swine, high-spatial-resolution gradient echo imaging (approximately 1 x 1 mm(2) in-plane resolution) was performed before and 5, 20, 40, and 60 minutes after intravenous administration of 12.3 micromol/kg EP-3600. Contrast was administered during stress induced by an infusion of 250 mumol x kg(-1) x min(-1) adenosine. Yb-DTPA was administered simultaneously for comparison of myocardium-to-plasma ratios. Images were assessed subjectively by 2 investigators, and signal-to-noise and contrast-to-noise ratios over time were calculated. Normal myocardium showed a significant signal-to-noise ratio increase during the entire examination time. In all animals (n=5), the perfusion defect in the left anterior descending artery territory could be visualized with a high contrast-to-noise ratio for at least 20 minutes after contrast injection. A significantly higher myocardium-to-plasma ratio was found for EP-3600 compared with the control agent Yb-DTPA (0.85+/-0.26 versus 0.22+/-0.08, respectively; P<0.01). EP-3600 is a new molecular MR imaging contrast agent that binds to the myocardium and enables prolonged, high-contrast, high-spatial-resolution visualization of myocardial perfusion defects.

Clinical significance of upper airway obstruction pattern during apneic episodes on ultrafast dynamic magnetic resonance imaging

Objectives In order to assess the relationship between upper airway obstruction pattern and the clinical characteristics of obstructive sleep apnea syndrome (OSAS), we evaluated dynamic changes in the pharyngeal airway of patients with the disorder by using ultrafast dynamic magnetic resonance imaging (MRI). Methods MRI while asleep was performed on 31 patients with OSAS (29 men, 2 women; mean age, 46.6 ± 8.2 years; mean body mass index, 26.7 ± 4.9 kg/m 2; mean AHI, 40.6 ± 21.7 episodes/h). Relationships between obstruction pattern focusing on differences between single-site obstruction (SO) and multiple-site obstructions (MO) and titrated value of nasal CPAP in addition to respiratory variables were investigated. Results The velopharynx (VP) was the main obstructive site among most of the cases with SO (17 of 18 cases), and all of the cases with MO ( n = 13) showed obstruction at and below the VP. AHI was significantly higher in cases with MO than in those with SO ( P < 0.01). As for SaO 2 variables, minimum value during sleep was significantly lower and total time with SaO 2 £90% was longer in cases with MO than in those with SO ( P < 0.05 each). Titrated value of n-CPAP was also significantly higher in cases with MO than in cases with SO ( P < 0.05). Conclusions Our results strongly suggest that formation of MO manifested on ultrafast dynamic MRI could be related to increased severity of the disorder. Considering the higher titrable value of CPAP, MO could be brought about by high pharyngeal pressure.

Fetale Magnetresonanztomographie des Gehirns

Fetal magnetic Resonance Imaging (MRI) is a valuable adjunct to ultrasonography (US) in prenatal diagnosis. The high spatial resolution, the large field-of-view, the different contrasts that can be generated and the development of functional MRI-sequences are especially valuable in the diagnosis of complex pathologies of the central nervous system. In addition, fetal MRI does not suffer from obscuring maternal or fetal osseous structures, intestinal gas or maternal obesitas. The ultrafast MRI sequences allow imaging without fetal sedation. Nowadays, fetal MRI is used to confirm, complete or correct US-findings in order to offer the best possible fetal treatment pre- and postnatally.

MR imaging of omphalopagus conjoined twins with a dandy-walker malformation: prenatal true FISP &amp; HASTE sequences

Conjoined twins are an extremely rare congenital malformation without any known genetic predisposition. Omphalopagus twins are the second most common variety of conjoined twins and usually are joined at the umbilicus. We present omphalopagus conjoined twins demonstrated with true FISP (fast imaging with steady-state procession) and HASTE (half- Fourier acquisition single-shot turbo spin-echo) magnetic resonance imaging (MRI) sequences, which showed Dandy- Walker malformation in one of the pair. To our knowledge, this is the first case of conjoined twins with this malformation, which was diagnosed with ultrafast MRI.

Angeborene Fehlbildungen der Aorta im Kindes- und Jugendalter

Aortic abnormalities are common cardiovascular malformations accounting for 15-20% of all congenital heart disease. Ultrafast CT and MR imaging are noninvasive, accurate and robust techniques that can be used in the diagnosis of aortic malformations. While their sensitivity in detecting vascular abnormalities seems to be as good as that of conventional catheter angiocardiography, at over 90%, they are superior in the diagnosis of potentially life-threatening complications, such as tracheal, bronchial, or esophageal compression. It has been shown that more than 80% of small children with aortic abnormalities benefit directly from the use of noninvasive imaging: either cardiac catheterization is no longer necessary or radiation doses and periods of general anesthesia for interventional catheterization procedures can be much reduced. The most important congenital abnormalities of the aorta in children and adolescents are presented with reference to examples, and the value of CT and MR angiography is documented.

Fetal Magnetic Resonance Imaging

Fetal magnetic resonance imaging (MRI) is emerging as an important complementary clinical tool to ultrasonography for evaluation of fetal anomalies. Fetal MRI has been in clinical use since 1983; but, early magnetic resonance (MR) sequences were of several minutes’ duration, resulting in significant fetal motion artifact. The recent development of ultrafast MRI sequences allows subsecond image acquisition, minimizing the artifact related to fetal motion. Accurate diagnosis of a fetal anomaly by MRI has the potential to improve parental counseling regarding prognosis and treatment options, assist clinicians with fetal and postnatal management decisions, and plan delivery at an appropriate center for treating the diagnosed anomaly. This review discusses MRI safety and techniques; clinical indications for fetal MRI; and the MR appearance of normal anatomy and anomalies involving the fetal neck, chest, and abdomen.

Uterine Contractility Evaluated on Cine Magnetic Resonance Imaging

The inherent contractility of the uterus has attracted concern of researchers and exhibits two known patterns of contraction. One is focal and sporadic bulging of the myometrium, and the other is rhythmic and subtle stripping movement in the subendometrial myometrium, known as uterine peristalsis. Recent development in the ultrafast magnetic resonance imaging (MRI) techniques has enabled us to observe these uterine contractions directly and noninvasively. Although the mechanisms and relationship of these two kinds of myometrial contractions and their relations to age, pharmaceutical administration such as oral contraceptives (OCs), and a variety of gynecologic and obstetrical problems are still under debate, cine MRI can be applied for directly monitoring changes of the uterus related to important uterine functions such as fertility and menstrual problems.

Oscillations in gas-fluidized beds: Ultra-fast magnetic resonance imaging and pressure sensor measurements

Ultra-fast Magnetic Resonance Imaging (MRI) and pressure sensor measurements have been applied to study: (i) pressure fluctuations, (ii) the eruption of bubbles at the top of a bed and (iii) the formation of bubbles in a gas-fluidized bed. Ultra-fast MRI has been applied for the first time to study the formation and eruption of bubbles; the technique is non-intrusive and provides measurements with good temporal and spatial resolutions. The MRI measurements revealed that bubbles are formed periodically, rather than randomly at a distributor, which in this case was a perforated plate. The frequency at which bubbles erupted from the top of the bed matched the frequency of the pressure fluctuations measured just above the distributor, where the measured pressure is predicted very well for the case of slug flow by Kehoe and Davidson's [P.W.K. Kehoe, J.F. Davidson, Pressure fluctuations in slugging fluidized beds, AIChE Symp. Ser. 128 (69) (1973) 34–40] correlation, originally developed for locations high up a bed. Both findings lead to the conclusion that the passage and eruption of bubbles at the top of a bed are the dominant cause of the pressure fluctuations, which are subsequently propagated downwards through the bed. Two new correlations are proposed for predicting the frequency of pressure fluctuations in a bubbling bed; both correlations agree well with experimental measurements. A modification of Baeyens and Geldart's [J. Baeyens, D. Geldart, An investigation into slugging fluidized beds, Chem. Eng. Sci. 29 (1974) 255–265] correlation predicts the frequency of pressure fluctuations when slugs are formed, but are not fully developed. The frequency of bubble formation, as measured by MRI, is equal to or higher than both the frequency of bubble eruption at the top of the bed and the frequency of pressure fluctuations, depending on the depth of the bed. The frequency of bubble formation is significantly lower than predicted by Davidson and Schüler's [J.F. Davidson, B.O.G. Schüler, Bubble formation at an orifice in an inviscid liquid, Trans. Inst. Chem. Eng. 38 (1960) 335–342] equation, originally developed for gas–liquid systems.