Specialised Techniques in Oral Radiology


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  • Specialised Techniques in Oral Radiology

    1. 1. Specialized radiographic techniques By Dr. Hassan M. Abouelkheir BDS, MSc, PhD
    2. 2. Objectives By the end of this lecture students will be able to: 1- Recognize specialized radiographic techniques that help them in diagnosis and treatment plane. 2- They will be able to choose the right technique needed for patient evaluation. 3- They will be familiar with modern technology in diagnostic imaging that will be available in hospitals.
    3. 3. Specialized Radiographic Techniques 1.Computed Tomography (CT). 2.Cone Beam Computed Tomography. 3. Magnetic Resonance Imaging. 4. Nuclear Medicine. 5. Ultrasonography.
    4. 4. 4- Computer Tomography (CT) scan: • It is a a radiographic technique that blends the concept of thin layer radiography (tomography) with computer synthesis of the image. • In 1972, Godfrey Hounsfield , a researcher working for EMI limited in England developed a prototype scanner based on image reconstruction.
    5. 5. Computed Tomography x-ray source 360° rotation detectors
    6. 6. Computed Tomography x-ray tube Fan beam collimator detectors
    7. 7. Computed Tomography (CT)Cont. • 1st type CT scanner consists of x-ray tube and an array of scintillation detectors both move around patient . • 2nd type where detectors forming a continous ring round pt and x-ray tube may move in a circle within the detector ring (incremental scanner) due to overlapping layers.
    8. 8. Computed Tomography (CT)Cont. • A new CT scanners have aqcuire image data in spiral or helical fashion. • It reduces multiplanner image reconstruction time to 12 seconds versus 5 minutes . • It reduce radiation dose to 75%.
    9. 9. CT Equipment and Image Formation: It consists of: • 1- Donut shaped scanning gantry: which contains x-ray source, detectors and electronic measuring devices. • 2- Motorized table used to position patient within gantry. • 3- x-ray power supplies and controls. • 4- viewing devices such as video monitors.
    10. 10. Computer tomography (cont.) • . X-ray tube and detectors (scintillation crystals or xenon gas) are arranged in either a rotating arc opposite the x-ray generator or in a 360°aray around patient’s body so rotate once per slice (1.5mm6mm) so reduce the time of scanning from original 30 min to 1-2 sec per slice
    11. 11. Computer tomography (cont.) • The x-ray beam attenuation data are collected in a grid pattern called a matrix . • Each square in the matrix is made up of a pixel which represents the x-ray attenuation of small finite volume of tissue (Voxel) or volume element. • Typical matrix sizes in CT are 256*256 or 512*512 pixels. • Each pixel is assigned CT number representing the density after x-ray attenuation .
    12. 12. Computed tomography (cont.) • Each voxel has a CT number or Hounsfield unite between -1000 (air) to +1000 (dense bone) and Zero (water). • Head CT scanning slices are usually made with 3mm slices while 3D reformatting 1-1.5mm. • The image can be reconstructed or manipulated for 3D construction without further exposure to pt. • 3D reformatting requires each original voxel shaped as rectangular parallel piped or solid as dimensionally altered into multiple cuboidal voxels (cuberills) → Interpolation process.
    13. 13. Computer tomography (cont.) • At the video monitor one can select a window width or the range of CT numbers that represented by pure white to pure black. • Window level or CT number that represent the middle of grey level scale to differentiate between soft and hard tissue.
    14. 14. Indications in Dentistry 1. Evaluation & extent of any suspected pathology in the head & neck, including tumors, cysts and infection. 2. Determination of the location and displacement of facial fractures in RTA pt (Road traffic accident)
    15. 15. Indications in Dentistry (cont.) 3- 3D construction for plastic or maxillofacial surgeons for planning reconstruction after facial trauma. 4- radiographic presurgical evaluation of the size and width of the jaw before Osseo -integrated dental implants insertion.
    16. 16. Advantages of CT Scan 1-Overcome the superimposition of structure. 2- image acquisition in cross-sectional or other planes. 3- Soft tissue imaging. 4- adjustment of radiographic contrast. Disadvantages: 1- high cost. 2- high pt’s dose. 3- metallic filling produce star artifacts. Artifacts: 1- partial volume artifact at the junction of soft and hard tissue . 2- Beam –Hardening artifact . 3- Metal artifact.
    17. 17. 5- Cone Beam Computed Tomography. • The imaging source-detector and the method of data acquisition distinguish cone beam tomography from traditional CT imaging. Traditional CT uses a high-output rotating anode X-ray tube, while cone beam tomography utilizes a low-power, medical fluoroscopy tube that provides continuous imaging throughout the scan. • Traditional computerized tomography records data with a fan-shaped X-ray beam into image detectors arranged in an arc around the patient, producing a single slice image per scan..
    18. 18. Cone Beam CT 1. Cone-shaped x-ray beam 2. 360-degree rotation around head 3. Scan time around 20 seconds 4. 2D or 3D images 5. Patient exposure = ½ AFM
    19. 19. Cone Beam CT tubehead flat-panel detector
    20. 20. Cone Beam Computed Tomography (cont) • Each slice must overlap slightly in order to properly reconstruct the images. The advanced cone beam technology uses a coneshaped X-ray beam that transmits into a solid-state area sensor for image capture, producing the complete volume image in a single rotation. The sensor contains an image intensifier and a CCD camera, or an amorphous silicon flat panel detector
    21. 21. Cone Beam Computed Tomography (cont) • The single-turn motion image-capture used in cone beam tomography is quicker than traditional spiral motion, and can be accomplished at a lower radiation dose as a result of no overlap of slices. This type of imaging exposes a patient to less radiation than traditional CT scanners. • The next generation of CBCT is “Ultra Cone Beam CT Scanners.” • Ultra CBCT imaging provides important information about the three-dimensional structure of blood vessels, nerves, soft tissue, and bone
    22. 22. Cone Beam Computed Tomography (cont) • Three-dimensional visualization software can shade images to differentiate varying densities of facial structures. Grayscale shading provides the ability to view the relationships of common internal anatomy.
    23. 23. 6- Magnetic Resonance Image (MRI): • The simplest atom in the body is hydrogen atom where it’s nucleus contains one proton and one neutron. Each proton has it’s own magnetic field with N &S poles inherent magnetism is called magnetic moment the net result of this random magnetism is zero.
    24. 24. • If external magnetic field is applied so protons will align themselves like compass needle so dipoles aligns with direction of external magnetic field. • Each nucleus acts as small gyroscope as it wobbles in tinny circle called precession and it’s fastness called precession frequency as it is known as Larmor frequency . • Determination of Larmor frequency of precession is called resonance frequency of vibration.
    25. 25. Magnetic Resonance Able to image soft tissue without contrast agents 1. Magnetic field aligns atoms (Hydrogen) 2. Radiowaves alter alignment 3. Atoms realign, releasing energy 4. Computer produces image NO IONIZING RADIATION
    26. 26. Magnetic Resonance radiofrequency coils sliding table Magnet
    27. 27. • If we apply Radiofrequency (RF) equal to Larmor frequency the nuclei flip changing their direction and aligned opposite to the external magnetic field. when this RF energy is removed the nuclei return back to their previous orientation. • This way of returning to normal is called relaxation and required time is called relaxation time. • During relaxation RF signals is emitted. This is called free induction decay (FID) from which the MR image is formed . Then mathematical calculation is applied on FID to produce details of the sample.
    28. 28. • We apply 90°pulse or 180°pulse RF. • MRI depends on 3 factors: • 1- Spin Density (SD): the quantity proportional to the number of nuclei in tissue precessing at Larmor frequency and contributing to MR signal. • 2- T1: the time required for interaction between nuclear spin and the tissue lattice to return to normal following RF excitation (spin-lattice relaxation time). • 3- T2: the time required for interaction between nuclear spins and adjacent nuclear spin (spinspin) to return to normal following RF excitation (0.5-1-5 Tesla)
    29. 29. Indications: • Investigations of intra cranial tumors and lesions. • TMJ dysfunction for detection of internal disc derangement. Advantages: • 1- No ionizing radiation . • 2- Image manipulation & high resolution. • 3- Super differentiation between hard & soft tissues. Disadvantages: • 1-Bone cortex doesn’t give MR signals , only bone marrow. • 2- long scanning time. • 3- contra indicated in pt having metallic implants. • 4- expensive.
    30. 30. 7- Radioisotope image: • Radionuclide imaging relies upon altering the pt by making the tissues radioactive and pt becoming the source of ionizing radiation. • Radioactive isotopes (radio nuclides) are used to visualize specific tissues from diagnostic images produced by Gamma camera or rectilinear scintillation detectors. • Radionuclides are conjugated with chemical material to be injected I.V. to accumulate in certain tissues (target tissue) so after preparation it is called radiopharmaceuticals. e.g. radiopharmaceuticals Tc+MPD →bone scan. • - Tc+ RBCS → blood. 99m 99m
    31. 31. Scintigraphy (Radionuclide Scan) 1. Radioactive pharmaceutical agent 2. Tissue specificity 3. Gamma rays emitted 4. Gamma camera
    32. 32. • Technetium 99m is commonly used in salivary gland and bone scanning. • It has 6.03hs half life, emit 140.5 Kev Gamma photons • The detected radiation is computer processed to eliminate unwanted background noise and reconstruction of image for both anatomical and functional aspects. • Abnormality can be detected by local increase (hot spot) or decrease (cold spot) in concentration of radionuclide. • Single photon emission computed tomography (SPECT) which rotate 360°,multiple detectors allows acquistion of data from a number of contiguous transaxial slices.
    33. 33. • Positron emission computed tomography (PET) 100 time sensitive than Gamma camera. • Pt is injected with positron-emitting radionulides generated in cyclotronwhich emit of two 551 Kev photons at 180°to each others. Advantages: 1- target tissue function. 2- computer analysis and enhancement. Disadvantages: 1- poor resolution. 2- Expensive. 3-Time consuming. 4-Contraindicated in pregnancy.
    34. 34. Advances in radionuclide imaging: Single photon emission computed tomography(SPECT): • Cross sectional image or SPECT scan enabling the exact anatomical site of the source of emission to be determined. Positron emission Tomography(PET): • Some isotopes decay by the emission of positively charged electron (Positron) from nucleus which interact with high energy Gamma rays to produce annihilation radiation that can be detected by PET . • It is used to investigate disease at molecular level and cross sectional slice is displayed even if there is no anatomical abnormalities appeared on CT or MRI scans.
    35. 35. 8- Ultrasound • Ultrasonography is medical imaging technique that uses high frequency sound waves and their echoes. • Ultrasound machine transmits high frequency (1-5 mega Hertz) sound pulses into the body using transducer probe. • These waves hit boundaries between tissues (fluid/softtissue/ bone). • Most of them are reflected back to be received by the same probe & relayed to machine.
    36. 36. Ultrasound 1. High-frequency ultrasonic vibrations 2. Echoes at tissue density differences 3. Varying echo intensities image NO IONIZING RADIATION
    37. 37. Ultrasound echoes
    38. 38. • The machine calculates the distance from the probe to tissue or boundaries using the speed of sound in tissue (1,540m/s) and time of each echo’s return (in millionths of second)
    39. 39. Transducer probe • • • • • Makes the sound waves and receives the echoes using principle called piezoelectric (pressure electricity) effect discovered by Pierre & Jacques curie in 1880. In probe there are one or more quartz crystals called piezoelectric crystals when electric current is applied , they vibrate producing sound waves that travel outside . At the same time when echo returned back to crystals causing vibration as a result of that they emit electric current . Therefore they used for sending & receiving sound waves. Cpu transfer electric impulses into a n image of topographic or cross sectional picture that represent the depth of tissue interfaces.
    40. 40. • Recently doppler effect can be used to measure a change of frequency of sound reflected from a moving source e.g. arterial, venous blood flow. • 3D doppler allow: • 1-early detection of cancerous and benign tumors. • 2- masses in colon & rectum. • 3- breast lesions for possible biopsy.
    41. 41. Indications: • 1- swelling in the neck. • 2- salivary gland & duct calculi. • 3- ass. Of ventricular system in babies. • 4- Obstetrics and Gynecology .
    42. 42. Disadvantages: • 1- Restricted use in head & neck as sound waves are absorbed by bone. • 2- Very operator dependant. • 3- Image is very difficult to interpret form inexperienced operator. • 4- Real time image.