Skeletal development on fetal magnetic resonance imaging.

Prenatal magnetic resonance imaging (MRI) is being increasingly used, in addition to standard ultrasound, for the diagnosis of congenital diseases beyond the central nervous system. Previous studies have demonstrated that MRI may be useful for the in utero visualization of spinal dysraphism and for differentiating between isolated and complex skeletal disorders with associated abnormalities. More recently, attention has focused on the visualization of the human fetal skeleton for the delineation of normal and pathological development of skeletal structures. On 1.5 T, in particular, echoplanar imaging enables the delineation of various epimetaphyseal structures and morphometric measurements of the fetal long bones from 18 gestational weeks until term. This information gathered from prenatal MRI might be helpful in the diagnosis of focal bone abnormalities and generalized skeletal disorders, such as bone dysplasias. Further clinical research, along with the refinement of the newest techniques, will enable expansion of the preliminary findings and help in determining the impact of fetal magnetic resonance bone imaging in the routine clinical setting. This review summarizes the current data in the literature and the authors' clinical experience with the magnetic resonance visualization of the developing fetal skeleton and also comments on the potential future applications of this technique.

Change in Modic type 1 and 2 signals after posterolateral fusion surgery.

STUDY DESIGN: Prospective cohort study. OBJECTIVE: To examine the change of Modic Type 1 to Type 2 after posterolateral fusion surgery. SUMMARY OF BACKGROUND DATA: Lumbar vertebral bone marrow change is divided into Modic types. Magnetic resonance imaging reveals Modic Type 1 and 2 signals. Some reports indicate that with time, Type 1 signals (intervertebral instability) change to Type 2 (restabilization), but the reliability of this assertion is unclear. The current study examines the change of Modic Type 1 signals to Type 2 after posterolateral fusion surgery. METHODS: Patients with Modic Type 1 and 2 signals were selected (mean age, 65 years). All patients suffered low back pain and leg pain due to lumbar spinal canal stenosis, and underwent decompression and posterolateral fusion surgery. We evaluated change in Modic signal and severity of low back pain (Visual analogue scale score, Japanese Orthopedic Association score, and Oswestry Disability Index before and 24 months after surgery. RESULTS: Of 21 patients with Modic Type 1 signals before surgery, 2 cases changed to normal bone marrow, 9 to Type 2, and 12 remained Type 1. Of 12 patients with Type 2 signals, none changed to Type 1, 2 changed to normal bone marrow, and 10 remained Type 2. Visual analogue scale score, Japanese Orthopedic Association score, and Oswestry Disability Index improved after surgery; however, low back pain was not significantly associated with signal change after surgery (P > 0.05). CONCLUSION: In the current study, Modic Type 1 signals changed to Type 2; however, Type 2 did not change to Type 1, suggesting that Type 2 signals indicate a stabilized stage. For Modic Type 1 and 2 signals, there were changes to normal bone marrow signals in 4 cases. Therefore, degenerated bone marrow may be able to regenerate after surgical stabilization. We did not show a significant difference between low back pain and signal type.

Diffusion-weighted imaging in patients with acute brain ischemia at 3 T: current possibilities and future perspectives comparing conventional echoplanar diffusion-weighted imaging and fast spin echo diffusion-weighted imaging sequences using BLADE (PROPELLER).

OBJECTIVES: To compare diffusion-weighted imaging (DWI) based on a fast spin echo (FSE) sequence using BLADE (PROPELLER) with conventional DWI-echoplanar imaging (EPI) techniques at 3 T and to demonstrate the influence of hardware developments on signal-to-noise ratio (SNR) with these techniques using 12- and 32-channel head coils. MATERIALS AND METHODS: Fourteen patients with brain ischemia were evaluated with DWI using EPI and FSE BLADE sequences, with a 12-channel head coil, in the axial plane and 1 additional plane (either sagittal or coronal). SNR and CNR were calculated from region-of-interest measurements. Scans were evaluated in a blinded fashion by 2 experienced neuroradiologists. SNR of both DWI techniques was evaluated in 12 healthy volunteers using different parallel imaging (PI) factors (for the EPI sequence) and both the 12- and 32-channel coils. RESULTS: DWI-BLADE sequences acquired with the 12-channel coil revealed a significant reduction in SNR (mean +/- SD) of ischemic lesions (SNR(lesion) [5.0 +/- 2.5]), normal brain (SNR(brain) [3.0 +/- 1.9]), and subsequently in CNR (3.0 +/- 1.8) as compared with the DWI-EPI sequence (SNR(lesion) [9.3 +/- 5.2], SNR(brain) [7.7 +/- 3.5], CNR [6.1 +/- 2.8], P < 0.001). Despite this reduction in SNR and CNR, the blinded read revealed a marked preference for the DWI-BLADE sequence, or equality between the sequences, in the majority of patients because lesion detection was degraded by susceptibility artifacts on axial DWI-EPI scans in 14% to 43% of cases (but in no instance with the DWI-BLADE sequence). In particular, preference for the DWI-BLADE sequence or equality between the 2 techniques for lesion detection in the brainstem and cerebellum was observed. On some DWI-BLADE scans, in the additional plane, radial-like artifacts degraded lesion detection.In volunteers, SNR was significantly improved using the 32-channel coil, irrespective of scan technique. Comparing DWI-EPI acquired with the 12-channel coil (iPAT = 2) to DWI-BLADE acquired with the 32-channel coil, comparable SNR values were obtained. The 32-channel coil also makes feasible, with DWI-EPI, an increase in the PI factor to 4, which allows for a further reduction of bulk susceptibility artifacts. However, still DWI-BLADE sequences performed better because of absence of bulk susceptibility artifacts at comparable SNR values. CONCLUSION: Despite lower SNR at comparable PI factors, DWI-BLADE sequences acquired using the 12-channel coil are preferable in most instances, as compared with DWI-EPI sequences, because of the absence of susceptibility artifacts and subsequently improved depiction of ischemic lesions in the brainstem and cerebellum. With the 32-channel coil, recently FDA approved, DWI-BLADE acquired with an iPAT = 2 provides comparable SNR without bulk susceptibility artifacts as compared with the DWI-EPI sequences acquired for clinical routine to date and has the potential to replace the standard DWI technique for special indications like DWI of the cerebellum and the brainstem or in presence of metallic implants or hemorrhage.

Fast and ultrafast non-echo-planar MR imaging techniques.

The topic fast and ultrafast MR imaging commonly includes relatively slow gradient-echo techniques with spoiled transverse magnetization (FLASH, FFE-T1, SPGR), gradient-echo techniques with partially refocused transverse magnetization (FISP, FFE, GRASS), gradient-echo techniques with fully refocused transverse magnetization (trueFISP, balanced FFE, FIESTA), the multi-echo spin-echo techniques (RARE, TSE, FSE), a mixture of multi-echo spin-echo and gradient-echo techniques (GRASE, TGSE), and finally single-shot techniques (HASTE, SS-FSE, EPI). This article gives a description of the sequence structures of non-echo-planar fast imaging techniques and a list of potential clinical applications. Recent advances in faster imaging which are not sequence related, such as simultaneous acquisitions of spatial harmonics (SMASH) and sensitivity encoding (SENSE) for fast MRI, are mentioned as well as some novel techniques such as QUEST and BURST. Due to the recent success with gradient-echo techniques with fully refocused transverse magnetization (trueFISP, balanced FFE, FIESTA), this "faster" gradient-echo technique is discussed in more detail followed by multi-echo spin-echo techniques that present the counterpart to the multi-echo gradient-echo (EPI) technique, which is not discussed in this paper. Three major areas appear to be the domain for EPI: diffusion; perfusion; and blood oxygenation level dependent imaging (BOLD, fMRI). For all other applications there is ample room for utilizing other fast and ultrafast imaging techniques, due to some intrinsic problems with EPI.

The development of magnetic resonance imaging in obstetrics.

Following recent developments in imaging techniques which overcome the problem of fetal motion, magnetic resonance imaging (MRI) has the potential to improve non-invasive fetomaternal assessment. This article catalogues the development of MRI and the potential that exists for its use in obstetrics in the future.