This review focuses on the current literature directed towards the brain metabolite findings in Cerebral Autosomal-Dominant Arteriopathy with Subcortical Infarcts and Leukoencephalopathy (CADASIL) disease using magneticresonance spectroscopy (MRS) and magneticresonancespectroscopicimaging (MRSI). Using search terms "metabolites", "spectroscopy", and "CADASIL", six articles were found on PubMed database, Scopus and Google Scholar. Changes in metabolites concentrations and relative ratios (RR) were found not only in abnormal but also in normal-appearing brain regions.
MagneticResonanceSpectroscopicImaging (MRSI) al- lows non-invasive investigation of regional metabolic processes in vivo, but suffers from long scan-times due to low metabolite concentrations, slow spatial encoding schemes, and low MR sensitivity (for nuclei other than protons). This versatile technique would benefit from a reduction in scan-time in order to make it more clinically applicable. Single- or multi-shot echo-planar spectro- scopic imaging (EPSI) sequences [1-6] have been proposed to reduce MRSI scan-time. Indeed, Furuyama et al. have evaluated the performance of CS EPSI based 2D J-resolved spectroscopy [7,8]. However, EPSI is known to provide lower sensitivity compared to classical chemical shift im- aging (CSI) . Low metabolite concentrations and re- duced MR sensitivity limit the applicability of parallel imaging. Conversely, Compressed Sensing (CS) is a tech- nique for accelerating the inherently slow data acquisition process, and is well suited for MRSI due to its intrinsic denoising effect . CS has been used to accelerate 1 H- [10,11], hyperpolarized 13 C- [12-14], 23 Na- , 31 P-MRSI , and multi-dimensional NMR experiments [17,18]. The scan time reductions ranged from 2- [15,13] to 18- fold . The application of CS to (pre-) clinical in vivo imaging necessitates thorough examination of the condi- tions under which it is robust. However, little systematic evaluation of the influence of SNR and spatial resolution on the achievable scan-time reductions and quantification of metabolite signals has been performed to date [7,13,19]. Whilst the work by Geethanath et al.  made an im- portant step forward in the use of CS-MRSI, it generated some debate regarding the reliability of its use in the clinic [20,21]. We present a detailed performance evaluation of the CS-reconstruction developed by Geethanath et al. in
Magneticresonance spectroscopy has been proposed as a complement to conventional imaging of brain tumors in order to improve the sensitivity and specificity of the diagnostic process. This technique operates by exciting and recording signals from a range of magneticresonance frequencies, allowing the identification and quantification of several biologically significant molecules containing proton groups that resonate in the appropriate frequency range. While initial in vivo applications of spectroscopy were limited to the acquisition of a single spectrum from one volume of tissue, recent developments have combined imaging and spectroscopy acquisition techniques to allow the simultaneous recording of spectra from a three- dimensional array of voxels. Magneticresonancespectroscopicimaging (MRSI) facilitates observation of the spatial distribution of metabolic patterns over a region of interest and surrounding tissue at a high spatial resolution (1.0 cc nominally). A number of spectroscopic studies of brain have reported the elevation of choline and reduction of N-acetyl aspartate (NAA) signals in neoplasm relative to normal cerebral tissue (Demaerel et al., 1991; Fulham et al., 1992; Negendank, 1992; Kinoshita et al., 1994; Vigneron et al., 1997), and have suggested use of the technique as a metabolic imaging complement to MRI. The use of MRSI in radiation therapy presents a clinically significant and technically challenging application of this technique. Radiation is commonly used as an adjunct or stand-alone treatment for neoplasms of the brain. However, the sensitivity and specificity of the imaging technique or techniques used to identify a target to treat with radiation limit the effectiveness of focal radiotherapy techniques, such as radiosurgery. Since it has already been shown to offer metabolic information unavailable from conventional MRI, MRSI offers an alternative target- selection method and may be able to refine and improve target selection for radiation therapy. This paper first briefly reviews conventional strategies for planning radiosurgical treatments based on MRI, as well as the fundamental aspects of the acquisition and reconstruction of MRSI data. We then outline a procedure for correlating MRSI findings with treatment planning imaging datasets, which will allow designation of a radiation target volume based on spectroscopic results. The differences in target delineation using imaging- and spectroscopy-based methodologies are then discussed, and the implications of these differences for clinical applications such as radiosurgery are examined. Finally, a novel treatment strategy incorporating MRSI for both the selection of
When MRI is not performed, no RF radiation is transmitted and the magnetic field is constant. Conversely, there is no fundamental change of state of the PET detector system between situations where imaging data is collected or not. A possible RF interference from the PET detector system to the 13 C-MRSI would depend on the PET gantry being powered on or off. However, no effect of power state is observed (Figs. 6, 7, and 8). The maximum 13 C-MRSI SNR error due to PET gantry power state is below −6 to +4 % (95 % CI) for all measurements. A tendency to temporal drift in the
MRS provided information about metabolic tis- sue composition, advanced spectroscopic me- thods had been used to quantify markers of brain tumor metabolism, (choline [Cho]), (cre- atine [Cr]), (N-acetyl-aspartate [NAA]), (lactate [Lac] or lipids) were the most commonly used parameters . Results were usually expre- ssed as ratios between brain metabolites. There were some studies have evaluated the diagnostic role of MRS for distinguishing glioma recurrence from radiation necrosis [14-16], nevertheless, the sensitivity and specificity of each research were different. Although many studies compared the effect between the DWI and MRS, but there were no uniform results [3-8]. Matsusue  reported that DWI had equivalent diagnostic efficiency with MRS and
The DCE technique is a more sensitive method of de- tecting synovitis than static contrast enhanced imaging. Axelsen et al. demonstrated in 17 RA patients that intra- operative knee synovial biopsies showed histological in- flammation which was highly correlated with changes in rates of synovial enhancement on pre-surgical T1 weighted MR images, especially the RER (spearman’s correlation co- efficient = 0.70, p = 0.001) . A review by Hodgson et al. was consistent with this; the RER was shown in multiple RA studies to correlate with histological, physiological and clinical disease activity changes . Synovitis assessed using DCE-MRI was more strongly associated with change in pain following steroid injection than static MRI imaging .
The use of breast MRI is increasing rapidly as this exciting technology improves and as data continue to become available supporting the value of this tool in select patient populations. Breast MRI is highly sensitive, with an acceptable specificity compared with other imaging modalities. Although MRI clearly detects cancers occult to mammography, ultrasound, and clinical breast exam, the impact of MRI on breast cancer recurrence or mortality has not been studied. Analyses of cost-effectiveness of MRI in distinct patient populations need to be performed. There is significant work to be done to optimize the application and performance of breast MRI. Research to clarify optimal acquisition protocols is needed. Recent work in breast MRI in 3 T magnets is very exciting and holds promise for even higher spatial and temporal resolution by providing a better signal : noise ratio. MRI spectroscopy, reviewed in another article in this series , may improve the specificity of MRI and might possibly predict the response to therapy and/or evaluate the very early response to chemotherapy. Novel contrast agents are being developed that may provide more sensitive and more specific discrimination of benign from malignant lesions. These rapidly advancing areas of research Table 1 Comparative sensitivity of screening methods in women at increased risk for breast cancer
Higher magnetic field strengths improve the SNR of MRI images, allowing images with higher spatial and/or temporal resolution to be acquired. However, the tissues imaged are exposed to greater specific absorption rates in higher magnetic field strengths, since the specific absorption rate scales approximately with the square of the static magnetic field. In a study performed on over 500 human subjects, it was shown that measured vital sign changes related to a sitting or supine position are larger than those associated with exposure to a static magnetic field of up to 8 T . Increase in the magnetic field strength dramatically increases magnetic susceptibility effects and related artifacts, such as errors in the correct attribution of tissue location, shape distortion, and signal intensity loss within the tissues. To minimize these effects and to avoid artifacts, MRI systems need to be carefully set up and the imaging protocols have to be tested on adequate phantoms before clinical MRI. Good shimming of the magnetic field together with the appropriate selection of the imaging protocol, the acquisition parameters, and the imaged geometry are, consequently, important in high-field clinical MRI. Other drawbacks of high-field MRI include acoustic noise and dielectric resonance . These problems have largely been resolved by improvements in hardware and software in MRI scanners . Higher magnetic field strengths also affect the relaxation properties and chemical shift in the region imaged . At higher field strengths, T 1 contrast tends to be minimized and T 2 contrast tends to be
Advances in magneticresonanceimaging (MRI) have enabled the non-invasive measurement of microvascu- lar blood flow without the need for gadolinium con- trast. One such method, called diffusion-weighted MRI (DW-MRI), measures the movement of water mole- cules in tissues, and is routinely used to identify micro- vascular perfusion deficits in the setting of acute brain ischemia . When combined with a mathematical post-acquisition technique called intravoxel incoherent motion (IVIM), microvascular perfusion can be quanti- fied as the perfusion (“f”) fraction . Consistent with the known perfusion impairment that occurs following ischemia-reperfusion injury , DW-MRI scanning has demonstrated reduced microvascular flow in transplant kidneys with DGF as compared to those with initial graft function [11 – 15]. To our knowledge, however, the natural history of changes in water mobility has never
Previous studies have attempted to quantify myocar- dial torsion using tissue Doppler imaging , or speckle tracing echocardiography . However, Doppler imaging cannot measure velocity in three dimensions and for all cardiac segments. Speckle tracking, while overcoming the previous limitations, is highly dependent on the acoustic window. Cardiovascular magneticresonance (CMR) is a powerful alternative for analyzing local myo- cardial deformation. Based on MR-Tagging [10, 11], the rapid and complex rotational motion pattern and the endo- versus epicardial differences of the heart muscle are difficult to quantify due to the low spatial resolution. Displacement-encoded image using stimulated echoes (DENSE)  and Tissue Phase Mapping (TPM)  can measure local motion with higher temporal (DENSE) and spatial (TPM) resolution respectively. Moreover, TPM directly measures myocardial velocities and allows for their quantitative assessment along all three principal motion directions of the heart (radial, long-axis, circumferential). Acceleration plays an import- ant role to make high resolution TPM acquisition pos- sible during breath hold. Existing methods employ spatio-temporal imaging acceleration k-t GRAPPA  (required breath hold: 25 heartbeats) and non-Cartesian SENSE implemented on the GPU  (required breath hold: 13–17 heartbeats).
Abstract: “Thoracic outlet syndrome” is a term that covers a range of conditions and abnormalities causing a variety of presentations and symptoms. In order to assess and treat this group of conditions, careful consideration needs to be given to individual presentations to tailor appropriate clinical and imaging tests. There is no single test available for the definitive diagnosis and assessment of this group of conditions. This article aims to present an up-to-date review with particular focus on the diagnosis and relevance of the different imaging modalities. Chest radiography allows identification of bony abnormalities and apical lung tumors. Ultrasonography is useful in cases of suspected acute thrombosis of the upper limb. Computed tomography com- bined with computed tomography angiography provides a useful overview of the anatomical and vascular structures. Magneticresonanceimaging and magneticresonance angiography are now widely used methods of assessment for vascular thoracic outlet syndrome, allowing dynamic assessment of the thoracic outlet, with good soft tissue contrast allowing for visualization of a wider range of pathologies than other imaging methods.
whereas partial weight bearing was recommended for 6 weeks after surgery on her right knee. Return to sports with full contact sports was allowed 4-6 months after refixation and 12 months after reconstruction with the AMIC technique. The rehabilitation did not proceed as fast as it did with her left knee. During the 12 months follow-up she still complained about recurrent instability during daily activities as well as temporary pain. She reported that both rehabilitation and pain reduction were significantly delayed in comparison to her contra- lateral knee joint. The 12-month Lysholm score for her left knee (95) documented a higher satisfaction in the follow-up examination in comparison to her right knee (78; see Table 1). Her magneticresonance obser- vation of cartilage repair tissue (MOCART) score was used to evaluate the articular cartilage repair tissue 12 months postoperatively (see Table 2). The MRIs of both knees preoperative and postoperative are shown in Figs. 1 and 2.
Figure 1-1: Abdominal opposed phase MRI image of a patient with NAFLD. Visible non- uniform distribution of fat content shows the possible sampling error when performing conventional liver biopsy. Arrow ‘a’ points to normal tissue, while arrow ‘b’ points to a region of steatosis. Steatotic regions appear dark because the water and fat signals have opposite phase and therefore the signal from fat partly cancels out the signal from water. ..... 4 Figure 1-2: For a collection of a large number of protons at thermal equilibrium, individual magnetization orients randomly, resulting in zero net magnetization. ..................................... 8 Figure 1-3: In the presence of a B 0 external magnetic field, there are only two orientations for
Computed tomography (CT) and magneticresonanceimaging (MRI) are the most commonly used non-invasive evaluation tools in the diagnosis and treatment of HCC and can provide useful pathological information. 6–8 Some studies have already reported evaluating tumor histological grade using diffusion-weighted imaging (DWI), but this functional MR imaging technique only reveals the Gaussian water diffusivity. 9,10 The recently developed dif- fusion kurtosis imaging (DKI) technique is based on the localized in vivo non-Gaussian diffusion of water mole- cules resulting from the structural and morphological com- plexity of the tissues (e.g., the intrinsic biochemical properties of different types of cells and tissues), which was ﬁ rst proposed by Jensen in 2005. 11,12 Compared to normal diffusion in the tissue, non-Gaussian diffusion has higher peak values. DKI can quantify the actual diffusion of water molecules and the degree of displacement from an ideal Gaussian distribution. In other words, DKI is mainly employed to detect the properties of non- Gaussian water molecules diffusion in tissues, and the results re ﬂ ect the microstructural complexity of the tissue. 9,13,14 The most representative parameter of DKI is mean kurtosis (MK), which is considered an indicator of the complexity of the tissue microstructure; MK is a dimensionless parameter that re ﬂ ects the restriction of the degree of diffusion. The intensity of MK depends on the complexity of the tissue structure with signi ﬁ cantly more restricted non-Gaussian diffusion in tumors. Mean diffusion diffusivity (MD) represents the non-Gaussian distribution corrected by the average apparent diffusion coef ﬁ cient (ADC); this value re ﬂ ects only the diffusion of water molecules. Currently, DKI has been used in the evaluation of many diseases, such as kidney and prostate malignancies, 15 – 17 and has shown a better performance for characterizing and grading tumors than conventional DWI. 18 Additionally, DKI typically can accurately describe the diffusion information and re ﬂ ect the