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In The Name of Allah The Most Beneficent The Most Merciful.

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Presentation on theme: "In The Name of Allah The Most Beneficent The Most Merciful."— Presentation transcript:

1 In The Name of Allah The Most Beneficent The Most Merciful

2 M.R.I Magnetic Resonance Imaging

3 Introduction In this presentation the topic under discussion will be MRI introduction Nuclear Spin Properties Block Diagram Applications Limitations

4 MRI  Magnetic resonance imaging (MRI) is a test that uses a magnetic field and pulses of radio wave energy to make pictures of organs and structures inside the body MRI introduction Intensity wise differentiation  Fathigh (whitish)  Muscleintermediate (gray)  Ligaments & Tendonslow (dark gray)  Immature Scarintermediate - low

5 History Background  In the 1950s, Herman Carr reported on the creation of a one-dimensional MRI image. Paul Lauterbur expanded on Carr's technique and developed a way to generate the first MRI images, in 2D and 3D, using gradients. In 1973, Lauterbur published the first nuclear magnetic resonance image. and the first cross-sectional image of a living mouse was published in January 1974 MRI introduction

6 Procedure Magnetic nuclei are abundant in the human body (H,C,Na,P,K) and spin randomly Since most of the body is H 2 O, the Hydrogen nucleus is especially prevalent Patient is placed in a static magnetic field Magnetized protons (spinning H nuclei) in the patient align in this field like compass needles Radio frequency (RF) pulses then bombard the magnetized nuclei causing them to flip around The nuclei absorb the RF energy and enter an excited state When the magnet is turned off, excited nuclei return to normal state & give off RF energy The energy given off reflect the number of protons in a “slice” of tissue Different tissues absorb & give off different amounts of RF energy (different resonances) The RF energy given off is picked up by the receiver coil & transformed into images MRI introduction


8 What kinds of nuclei can be used for ?  Nucleus needs to have 2 properties:  Spin  charge  Nuclei are made of protons and neutrons  Both have spin ½  Protons have charge  Pairs of spins tend to cancel, so only atoms with an odd number of protons or neutrons have spin  Good MR nuclei are 1 H, 13 C, 19 F, 23 Na, 31 P MRI introduction

9 Hydrogen atoms are best for MRI  Biological tissues are predominantly 12 C, 16 O, 1 H, and 14 N  Hydrogen atom is the only major species that is MR sensitive  Hydrogen is the most abundant atom in the body  The majority of hydrogen is in water (H 2 O)  Essentially all MRI is hydrogen (proton) imaging Nuclear Spin Properties

10 A Single Proton + + + There is electric charge on the surface of the proton, thus creating a small current loop and generating magnetic moment . The proton also has mass which generates an angular momentum J when it is spinning. J  Thus proton “magnet” differs from the magnetic bar in that it also possesses angular momentum caused by spinning. Nuclear Spin Properties

11 How do protons interact with a magnetic field ?  Moving (spinning) charged particle generates its own little magnetic field  Such particles will tend to line up with external magnetic field lines (think of iron filings around a magnet)  Spinning particles with mass have angular momentum  Angular momentum resists attempts to change the spin orientation (think of a gyroscope) Nuclear Spin Properties

12 Machine Working

13 Application  Clinical neurology – Segmentation and classification – Measuring volumes of brain structures – Multiple sclerosis, stroke, …  Cardiology – Either need to image fast, or deal with heart motion!  Cancer –colorectal, liver, prostate, …  Soft tissue damage – Cartilage, ligaments, …

14 Limitations of MRI  Some patients experience claustrophobia and have difficulty in cooperating with the study.  Some obese patients cannot be examined.  Some patients, particularly acutely ill patients, cannot cooperate and movement artifacts may result.  Patient throughput is slow compared with other imaging modalities.  Patients with pacemakers and certain ferromagnetic appliances cannot be studied.  Greater technological expertise is required for performance of MRI than for most other imaging modalities.  MRI equipment is expensive to purchase, maintain, and operate.



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