CT image quality and image resolution.pptx

CT IMAGE QUALITY AND IMAGE RESOLUTION ARE DESCRIBED IN DETAILIN THIS PPT. CONTENT TAKEN FROM MUTIPLE BOOKS AND GENERALS.

1. CT image quality and image resolution MR. ROHIT BANSAL ASISTANT PROFESSOR MAMC (AGROHA)

2. Image quality refers to the visibility of diagnostically important structures in the CT image. CT image quality is influenced by many technical parameters. The image quality is influenced by five basic factors: Spatial Resolution. Image Contrast. Temporal Resolution. Image Noise. Image Artifacts.

3. Resolution is a term used to describe the ability to differentiate between structures. In diagnostic imaging, resolution refers to the number of pixels in an image. A high-resolution image has more pixels, which allows its to display more details. Resolution

4. It is the ability of the CT scanner to display separate images of two objects which are placed close together. In digital imaging, it depends on the size of the pixel used. A large pixel size will be unable to differentiate between two near-by objects as compared to a small pixel size. Spatial resolution is measured in line-pairs per millimeters. Spatial Resolution

5. Focal Spot- Smaller focal spots give a higher resolution. Thus, the Spatial Resolution improves. Detectors width- If the width of the detector is small, it gives a higher resolution. Thus Spatial Resolution improves. Number of Projections- A larger number of projections gives a finer resolution. Thus Spatial Resolution improves. Slice thickness- Thinner slices produce sharper images. If the slice is thinner, it gives a higher resolution. Thus Spatial Resolution improves. Kernels- Sharp kernels have better spatial resolution than soft kernels. Pitch- Lower pitch ratio improves spatial resolution. Pixel Size- Smaller Pixel Size gives more detail. Thus Spatial Resolution improves. FOV- Smaller FOV gives a finer resolution. Thus Spatial Resolution. Patient Motion- If the patient's motion decreases, thus the Spatial Resolution increases. Factors Affecting Spatial Resolution

6. It is the ability of the CT scanner to display the object with considerably different in density from its surrounding objects. In digital imaging, it depends on the bit-depth of the system. The 8-bit system shows less gray values - 256 gray values, and the 12-bit system that shows 4096 gray values. If the system can clearly show two near-by gray value intensities, the system will have a high contrast resolution. Contrast Resolution

7. Increases in mAs , improve contrast resolution. Decreases in pixel size decreases contrast resolution. Increases in Slice thickness improves contrast resolution. Increases in FOV improves contrast resolution. Factors Affecting Contrast Resolution

8. Temporal resolution is the duration of time for the acquisition of image. In cardiac CT, it is necessary to image the beating heart in milliseconds. In cardiac CT, the temporal resolution of 3 second means that a single image is acquired within 3 seconds of the cardiac cycle. In a fast MDCT scanner, the temporal resolution will be better and the motion artifacts will be lesser. Temporal Resolution

9. Noise is defined as the grainy appearance of cross-sectional imaging. Noise decreases in the picture quality and reduces the contrast resolution. Noise is caused by a low photon count in an image. Noise is measured by the signal to noise ratio (SNR). NOISE

10. The number of X-ray photons detected per pixel is also often referred to as signal-to-noise ratio (SNR). The higher the ratio, the less noise is present in the image. The noise is caused by many factors; the most common is quantum mottle. Quantum Mottle - Quantum mottle occurs when there is an insufficient number of photons detected by the detector. Signal to Noise Ratio (SNR)

11. Decreases in pixel size increase the noise. Increases in mAs , decreases the noise. Larger patients will absorb more radiation hence fewer photons will reach the detector, which will reduce the signal-to-noise ratio. Factors Affecting CT Noise

12. CT scanner generates a high dose of radiation. These radiations alter the tissue and produce free radicals, which can lead to cancer. Factors Affecting CT Dose Increases in mAs , increase the patient dose. Increases in kVp without a decrease in mAs , increase the patient dose. Increases in image quality, increase the patient dose. Decreases in slices thickness increase the patient dose. Patient Dose

13. The patient's dose in CT scan examination can be reduced by following steps By reducing the tube current ( mA ) By Increasing the table pitch. By adjusting the mA settings manually, according to patient weight. By reducing the number of multiple scans. Effective Radiation Dose in Adults for CT Scan Procedure • Computed Tomography Abdomen and Pelvis-10 mSv (Approximate) • Computed Tomography Chest-7 mSv (Approximate) • Computed Tomography Angiography- 12 mSv ( Approximate) ● Computed Tomography without contrast Head- 2 mSv (Approximate) Reduction of Patient dose in CT Procedure

14. ICRP EFFECTIVE RADIATION DOSE IN ADULTS ABDOMINAL REGION Procedure Approximate effective radiation dose Comparable to natural background radiation for: Computed Tomography (CT)–Abdomen and Pelvis 7.7 mSv 2.6 years Computed Tomography (CT)–Abdomen and Pelvis, repeated with and without contrast material 15.4 mSv 5.1 years Computed Tomography (CT)–Colonography 6 mSv 2 years Intravenous Urography (IVU)  3 mSv 1 year Barium Enema (Lower GI X-ray) 6 mSv 2 years Upper GI Study with Barium 6 mSv 2 years

15. BONE   Procedure Approximate effective radiation dose Comparable to natural background radiation for: Lumbar Spine 1.4 mSv 6 months Extremity (hand, foot, etc.) X-ray Less than 0.001 mSv Less than 3 hours CENTRAL NERVOUS SYSTEM Procedure Approximate effective radiation dose Comparable to natural background radiation for: Computed Tomography (CT)–Brain 1.6 mSv 7 months Computed Tomography (CT)–Brain, repeated with and without contrast material 3.2 mSv 13 months Computed Tomography (CT)–Head and Neck 1.2 mSv 5 Months Computed Tomography (CT)–Spine 8.8 mSv 3 years

16. CHEST Procedure Approximate effective radiation dose Comparable to natural background radiation for: Computed Tomography (CT)–Chest 6.1 mSv 2 years Computed Tomography (CT)–Lung Cancer Screening 1.5 mSv 6 months Chest X-ray 0.1 mSv 10 days DENTAL Procedure Approximate effective radiation dose Comparable to natural background radiation for: Dental X-ray 0.005 mSv 1 day Panoramic X-ray 0.025 mSv 3 days Cone Beam CT 0.18 mSv 22 days

17. HEART Procedure Approximate effective radiation dose Comparable to natural background radiation for: Coronary Computed Tomography Angiography (CTA) 8.7 mSv 3 years Cardiac CT for Calcium Scoring 1.7 mSv 6 months Non-Cardiac Computed Tomography Angiography (CTA) 5.1 mSv Less than 2 years MEN'S IMAGING   Procedure Approximate effective radiation dose Comparable to natural background radiation for: Bone Densitometry (DEXA) 0.001 mSv 3 hours

18. NUCLEAR MEDICINE   Procedure Approximate effective radiation dose Comparable to natural background radiation for: Positron Emission Tomography–Computed Tomography (PET/CT) Whole body protocol 22.7 mSv 6 years WOMEN'S IMAGING Procedure Approximate effective radiation dose Comparable to natural background radiation for: Bone Densitometry (DEXA) 0.001 mSv 3 hours Screening Digital Mammography 0.21 mSv 26 days Screening Digital Breast Tomosynthesis (3D Mammogram) 0.27 mSv 33 days

19. ACR EFFECTIVE RADIATION DOSE IN ADULTS Single Radiograph Effective Dose, mrem (mSv) Skull (PA or AP) 1 3 (0.03) Skull (lateral) 1 1 (0.01) Chest (PA) 1 2 (0.02) Chest (lateral) 1 4 (0.04) Chest (PA and lateral) 2 6 (0.06) Thoracic spine (AP) 1 40 (0.4) Thoracic spine (lateral) 1 30 (0.3) Lumbar spine (AP) 1 70 (0.7) Lumbar spine (lateral) 1 30 (0.3) Abdomen (AP) 1 70 (0.7) Abdomen 3 53 (0.53) Pelvis (AP) 1 70 (0.7) Pelvis or hips 3 83 (0.83) Bitewing dental film 3 0.4 (0.004) Limbs and joints 3 6 (0.06)

20. Complete Exams Effective Dose, mrem (mSv) Intravenous pyelogram (kidneys, 6 films) 1 250 (2.5) Barium swallow (24 images, 106 sec fluoroscopy) 1 150 (1.5) Barium meal (11 images, 121 sec fluoroscopy) 1 300 (3.0) Barium follow‐up (4 images, 78 sec fluoroscopy) 1 300 (3.0) Barium enema (10 images, 137 sec fluoroscopy) 1 700 (7.0) CT head 1 200 (2.0) CT chest 1 800 (8.0) CT abdomen 1 1,000 (10) CT pelvis 1 1,000 (10) CT (head or chest) 2 1,110 (11.1) PTCA (heart study) 3 750–5,700 (7.5–57) Coronary angiogram 3 460–1,580 (4.6–15.8) Mammogram 3 13 (0.13) Lumbar spine series 3 180 (1.8) Thoracic spine series 3 140 (1.4) Cervical spine series 3 27 (0.27)