Factors for MRI Image Quality

Factors for magnetic resonance imaging form QualityTitle magnetic resonance imaging Image QualityTABLE OF table of contents1.0 INTRODUCTION2.0 designate TO intervention RATIO (SNR)Figure 13.0 line of products TO NOISE RATIO (CNR)4.0 RESOLUTION AND SCAN cartridge clip5.0 THE RELATIONSHIP surrounded by magnetic resonance imaging PARAMETERS AND IMAGE QUALITYTable 1 magnetic resonance imaging parameters trade-offs (Proprofs.com, 2015)6.0 refinementREFERENCES1.0 INTRODUCTIONImage quality is the most important element in imaging radiography. According to Courses Washington Education, (2015) catch quality must be assessed on the basis of just performance of some task of enkindle by some observer or decision maker. It was stated that image quality must be defined in terms of a task on what information to be retrieved from an image and the observer on how the information will be extracted from the image.Since MRI image is a digital image, it is greatly depends on image contrast and its spacial characteristics. Nevertheless, one of the disadvantages of this flexibleness is a greater difficulty in terms of the choice of see parameters. In general scan measures are not minimal and there is a certain tendency towards artefact. However, the most fundamental terminus ad quem in MRI is the point-to go ratio (SNR) which is dependent upon the hardware, mostly the briny empyrean strength and radiofrequency (RF) coils, upon the relaxation properties of tissue and upon the choice of sequence parameters. candid image quality depends upon making sizeable scanning parameter choices (McRobbie, 2007).2.0 SIGNAL TO NOISE RATIO (SNR)The signal to noise ratio can be defined as the ratio of the amplitude of the signal wind to the average amplitude of the noise whereas the signal is the voltage induced in the liquidator coil by the precession of the net magnetic vector in the transverse plane (Westbrook et al. 2011, pp.104).Noise can be defined as an undesirable backgro undinterferenceor disturbance that sees image quality (Mr-tip.com, 2015). According to Weber (2015), noise is caused by two agentive roles which are the electromagnetic noise in the carcass due to gesture of charged particles and small anomalies in the pass judgmentment electronics, which depends on the size of the RF coil and the bandwidth of the pulse sequence.In addition, noise occurs at all frequencies and is also random in time and space. On the otherwise hand, the signal is cumulative, and occurs at time TE, depends on many factors and it can be altered. The signal is therefore can be changed in relation to the noise. amplify the signal increases the SNR, while decreasing the signal decreases the SNR. Therefore, any factor that affects the signal amplitude in gives effect to the SNR. The factors that affect the SNR include magnetic field strength, the proton density, voxel volume, repetition time (TR), echo time (TE), flip angle, summate of excitations (NEX), receive b andwidth and coil type (Westbrook et al. 2011, pp.104).According to McRobbie in his book, MRI from Picture to Proton (2007), images with a poor SNR will appear fuzzy. An important aspect of image optimisation is to certify that there is a high enough SNR for the images to be diagnostically semiprecious yet low SNR whitethorn result in losing small inside information or the obscuring of subtle contrast changes. Therefore, contrast to noise ratio (CNR) is unendingly taken into consideration in the aspect of image quality.Figure 1 Increasing the basic announcement will increase the image quality. However, increase the occlusion much than the acceptable range will produce grains in the image due to low SNR and reducing it will produce a blurry image due to high SNR. Increasing basic dissolvent will result in prolonged time. (Image adapted from Mrimaster.com, 2015)3.0 CONTRAST TO NOISE RATIO (CNR)CNR can be defined as a measure to assess the ability of an imaging procedure to gene rate clinically utile image contrast. However, the image contrast itself is not precise enough to restrict an image, because in a noisy image it is uncertain where the contrast originates. It depends on two factors either due true tissue contrast, or it whitethorn be due to noise fluctuations. The human ability to distinguish in the midst of objects is proportional to contrast, and it decreases linearly with noise (KTH, 2015).By improving CNR the perception of the obvious differences between two clinical areas of interest will be increased. In a simple word, acontrasttonoiseratio is a summary ofSNRandcontrast. It is the difference inSNRbetween two relevant tissue types (Mr-tip.com, 2015).CNR is controlled by the same factors that affect SNR. However, it is considered as the most deprecative factor affecting image quality (scrsl.weebly.com, 2015).4.0 RESOLUTION AND SCAN TIMEIn MRI imaging, the scan time is advisable to be as trivial as possible. This is because the longer the u nhurried lies on the table the much likely it is that they will move. Moreover, if the patient has moved during the scan, the image produced will eat a great SNR (Westbrook et al. 2011).The minimum scan time in MRI imaging is affected by TR, matrix size and NEX while the spatial resolution is determined by matrix size, FOV and slice thickness. By change magnitude matrix size or decreasing FOV and slice thickness increases spatial resolution at the expense of either decreased signal-to-noise or increased scan time. In order to obtain images of high resolution with high signal-to-noise requires longer scan times. All of the scan parameters affect signal-to-noise ratio. However, the signal within an image can be raise either by increasing TR, FOV, slice thickness and NEX or by decreasing TE and matrix size. The most direct way to increase signal is by increasing NEX, but increasing NEX from two to cardinal which doubles the scan time, increases the signal by only the square first of two. Lastly, TE does not affect scan time however, it does determine the utmost number of slices in multi-slice mode. Increasing the TE or shortening TR decreases the number of slices that can be obtained with one pulse sequence (Spinwarp.ucsd.edu, 2015).5.0 THE RELATIONSHIP among MRI PARAMETERS AND IMAGE QUALITYAn image that is obtained in a short scan time, with a good spatial resolution and high SNR is favorite(a) yet is hardly to achieve as increasing one factor certainly trends one or both of the other two (Westbrook et. al, 2011).Trade-offsexists when changing imaging parameters to obtain the best images possible. For instance, the SNR, resolution, and erudition time, are all interconnected. changing one will affect the others. It is important to decide what factors are more important for an examination of a particular body part, patient and surmise abnormality.For example, when looking at the pituitary or cranial nerves, some SNR may need to be less considered or use longer acquisition time to improve the spatial resolution. However, in a claustrophobic of patient in pain who may be moving around, both resolution and SNR for the shortest possible examination time need to be considered to produce correct image quality and preventing motion artefact (Ballinger, 2015). Thetable below summarizes the trade-offs in MRI between SNR, resolution, time, maximum number of slices and distance covered.Table 1 MRI parameters trade-offs (Proprofs.com, 2015)6.0CONCLUSIONIn conclusion, the quality of an MR image depends on several factors which include the spatial resolution and image contrast, SNR and CNR and also artefacts. An MR examination is cooperation between scan time and image quality and its sequence parameters will have to be optimized in function of the organs and pathology.Moreover, the signal intensities and contrast are determined by the timing parameters TR and TE and also the flip angle. Besides, to produce a good image in MRI the scan time should always be as short as possible to avoid patient movement by using the shortest TR possible, select the coarse matrix possible and reduce the NEX to a minimum.REFERENCESBallinger, J. (2015).Trade offs Radiology Reference Article Radiopaedia.org. online Radiopaedia.org. on hand(predicate) at http//radiopaedia.org/articles/trade-offs Accessed 3 whitethorn 2015.Barrett, H. and Myers, K. (2004).Foundations of image science. Hoboken, NJ Wiley-Interscience.Courses Washington Education, (2015).Image Quality. online accessible at http//courses.washington.edu/bioen508/Lecture1_partC.pdf Accessed 30 Apr. 2015.KTH, (2015).Point Spread Function. online Available at http//medim.sth.kth.se/6l2872/F/F9.pdf Accessed 30 Apr. 2015.McRobbie, D. (2007).MRI from picture to proton. Cambridge, UK Cambridge University Press.Mrimaster.com, (2015). MRI resolution and image quality how to manipulate mri scan parameters. online Available at https//mrimaster.com/index.4.html Accessed 4 May 2015.Mr-t ip.com, (2015).MRI Database Contrast to Noise Ratio. online Available at http//www.mr-tip.com/serv1.php?type=db1dbs=Contrast+to+Noise+Ratio Accessed 30 Apr. 2015.Mr-tip.com, (2015).MRI Database Magnetic plangency imagination MRI. online Available at http//www.mr-tip.com/serv1.php?type=db1dbs=Magnetic Resonance Imaging MRI Accessed 28 Apr. 2015.Mr-tip.com, (2015).MRI Database Noise. online Available at http//www.mr-tip.com/serv1.php?type=db1dbs=Noise Accessed 30 Apr. 2015.Nde-ed.org, (2015).Image Considerations. online Available at https//www.nde-ed.org/EducationResources/CommunityCollege/Radiography/TechCalibrations/imageconsiderations.htm Accessed 30 Apr. 2015.Proprofs.com, (2015).Flashcards Table on MRIImaging Parameters. online Available at http//www.proprofs.com/flashcards/tableview.php?title=mriimaging-parameters Accessed 3 May 2015.scrsl.weebly.com, (2015).Parameters and Trade-offs. online Available at http//scrsl.weebly.com/uploads/5/1/3/0/5130772/magnetic_resonance_imag ing_6parameters__trade_offs.ppt Accessed 30 Apr. 2015.Spinwarp.ucsd.edu, (2015). online Available at http//spinwarp.ucsd.edu/neuroweb/ schoolbook/br-100.htm Accessed 3 May 2015.Spinwarp.ucsd.edu, (2015). online Available at http//spinwarp.ucsd.edu/neuroweb/Text/br-100.htm Accessed 3 May 2015.UChicago, (2015).How does MRI work?. online Available at http//wiki.ci.uchicago.edu/pub/HNL/DifficultQuestion/howdoesmriwork.pdf Accessed 30 Apr. 2015.University of Bergen, (2015).Contrast (CNR) in MRI. online Available at https//wikihost.uib.no/mriwiki/images/5/5c/MRCourseLectures_Oct2011_ContrastTheory.pdf Accessed 30 Apr. 2015.Weber, D. (2015).MRI Quality. online Psdlw.users.sourceforge.net. Available at http//psdlw.users.sourceforge.net/ locomote/dweber_docs/mri_quality.html Accessed 30 Apr. 2015.Westbrook, C. and Kaut-Roth, C. (2011).MRI in practice. Oxford Blackwell Science.1