General Overview of Radiology (TG05-CG13) (V2) PDF

General Overview of Radiology Module 01: Principles & Perspectives II Reza Koa-Sales, MD | August 24, 2023 TABLE OF CONTENTS I. OVERVIEW.........................................................................................1 II. CONVENTIONAL RADIOGRAPHY..............................................

General Overview of Radiology Module 01: Principles & Perspectives II Reza Koa-Sales, MD | August 24, 2023 TABLE OF CONTENTS I. OVERVIEW.........................................................................................1 II. CONVENTIONAL RADIOGRAPHY...................................................... 1 A. BASIC PRINCIPLES........................................................................ 1 B. PRINCIPLES OF INTERPRETATION................................................. 2 C. SAMPLE RADIOGRAPHS............................................................... 3 III. ULTRASONOGRAPHY...................................................................... 4 A. ULTRASOUND IMAGE PRODUCTION............................................4 B. PRINCIPLES OF INTERPRETATION................................................. 4 C. TYPICAL APPEARANCE OF TISSUES...............................................5 D. SAMPLE ULTRASOUND IMAGES................................................... 5 E. DOPPLER ULTRASOUND............................................................... 6 F. ULTRASOUND ADVANTAGES AND DISADVANTAGES..................... 6 IV. COMPUTED TOMOGRAPHY (CT)..................................................... 6 A. CT SCAN IMAGE PRODUCTION.................................................... 6 B. PRINCIPLES OF INTERPRETATION................................................. 6 C. CT ADVANTAGES AND DISADVANTAGES.......................................7 D. SAMPLE CT IMAGES..................................................................... 7 V. MAGNETIC RESONANCE IMAGING (MRI)......................................... 8 A. MRI IMAGE PRODUCTION............................................................8 B. MRI SIGNAL INTENSITIES..............................................................8 C. MRI ADVANTAGES AND DISADVANTAGES.................................... 8 VI. NUCLEAR IMAGING........................................................................ 8 A. BASIC PRINCIPLES........................................................................ 8 B. NUCLEAR IMAGING ADVANTAGES AND DISADVANTAGES........... 8 C. NUCLEAR IMAGING MODALITIES................................................. 8 VII. TERMINOLOGIES........................................................................... 9 A. CONVENTIONAL RADIOGRAPHY (DENSITY)................................. 9 B. ULTRASONOGRAPHY (ECHOES)....................................................9 C. CT SCAN (DENSITY).......................................................................9 D. MRI (INTENSITY).......................................................................... 9 E. NUCLEAR IMAGING (INTENSITY)................................................ 10 VIII. SAMPLE RADIOLOGIC IMAGES.................................................... 10 QUESTIONS............................................................................................ 12 ANSWER KEY..................................................................................... 13 RATIONALE..............................................................................................13 LEARNING OBJECTIVES 1. Understand the general concepts and imaging patterns in radiopathologic imaging 2. Recognize normal radiographic anatomy to help identify pathologic images 3. Enumerate the different imaging modalities available for radiopathologic imaging 4. Familiarize with terminologies used in describing radiographic findings ○ Magnetic Resonance Imaging (MRI) ○ Nuclear Imaging ● These imaging modalities are available in most hospitals ○ Other imaging modalities include electric imaging and scintigraphy, but they are not as available II. CONVENTIONAL RADIOGRAPHY ● Also known as x-ray ● Cornerstone imaging technique ○ Frequently requested ○ 150 to 300 x-rays are requested each day A. BASIC PRINCIPLES RADIOGRAPH PRODUCTION ● The x-ray tube generates a beam of x-ray ● The x-ray beam is transmitted through the body (absorbed, avoided/scattered, pass through) ● X-rays that pass through are recorded in a detector producing an image (film/digital image) ○ Most hospitals use digital images Figure 1. Diagram of how an X-ray is produced RADIOGRAPH INDICATIONS ● Interns should know the the purpose for requesting an imaging study (also called the indication) ○ Ask the following questions: ▸ What are the usual reasons for requesting an imaging study? ⎻ What does the patient have? ⎻ It is not enough to say, “I was just tasked to get this patient’s x-ray” ▸ Why are we using this modality? ▸ What is the indication for the radiologic examination? I. OVERVIEW ● Imaging techniques ○ Conventional Radiography (x-ray) ○ Ultrasonography = Ultrasound = Sonography = Sonogram ○ Computed Tomography scan (CT scan) YL6:01.34 TG05: Artillaga, Avila, Cheng, Escalante, Lim, Marcos, Palencia, Quimson, Remitio, Salvador, Sandoval CG13: Abad Santos, Ahalajal, Alba, Bernardo, Binobo, Cai, Dy, Gamboa, Pacis, Rejuso, Tan 1 Figure 2. KUB plain x-ray ● An abdominal x-ray shows the diaphragm while a KUB x-ray does not ○ An abdominal x-ray usually assesses rupture of the bowels ○ This manifests as air outside the bowels ○ The air goes up under the diaphragm because of its lighter weight ○ Hence, it is important to see the diaphragm in an abdominal x-ray ● One sample indication for a KUB x-ray is a kidney stone Figure 4. Knee x-ray. Femur (blue), tibia (red), fibula (yellow) ● Fracture: common indication for knee x-ray ○ X-ray is the imaging of choice for fractures because it produces the fastest result ○ Only do CT scans for more complicated fractures such as facial fractures Figure 3. Chest x-ray. (a) PA view, (b) lateral view ● Chest x-ray is the most commonly requested x-ray ● Possible indications for chest x-ray include: ○ Cough ○ Cardiovascular diseases ● In a chest X-ray, it's similar to seeing the patient's chest from the front ○ PA view: the left side of the image is called the radiologic right (signifies the right side of the patient) ○ The cardiac shadow points to the patient’s left side ● Situs inversus: rare genetic condition in which the organs in your chest and abdomen are reversed ○ Can be detected by x-ray ▸ Especially important to detect this condition prior to surgery Nice to Know! ● If the patient can afford it, do diagnostic tests to help both the patient and the physician YL6:01.34 General Overview of Radiology Figure 5. Patella (sunrise view) with a lateral patellar dislocation ● Sunrise view: Best view to see where the patella is in reaction to the femur ○ The "sunrise view" is like taking a picture of the kneecap from below to above ○ The patient is in a semi-recumbent position (or sitting partly upright on the table) ○ This helps see the kneecap in a special way within its groove (Larose & Bui-Mansfeild, 2019) ● Pathology in Figure 5: Patella should be at the center, but is seen at the side B. PRINCIPLES OF INTERPRETATION ● Attenuation ○ The reduction of the force, effect, or value of something ▸ Decreasing the effect or the intensity ⎻ Of the beam (x-ray) ⎻ Of the sound waves (ultrasound) ▸ Similar to impedance ○ Attenuation is the result of several features of X-ray or sound wave interaction with tissue and tissue boundaries, including: ▸ Absorption ▸ Scatter 2 ▸ Reflection ▸ Refraction ▸ Divergence ○ Tissues exhibit different capacities to attenuate x-rays ▸ White structures: MOST attenuating (i.e., most dense) ▸ Blackstructures: LEAST attenuating (i.e., least dense, allows beam to pass) ○ Tissues exhibit varying shades of gray, depending on density and thickness ▸ The denser the tissue, the more x-rays are attenuated ⎻ Bone:↑density, absorbs well ⎻ Muscle:↓density, absorbs less ⎻ Air:↓density, absorbs the least Figure 6 ABNORMAL FINDINGS Figure 8. Abnormal Chest X-ray (Pleural Effusion) ● Pleural effusion ○ Has fluid accumulation that obscures structures (diaphragm, costophrenic sulcus) Figure 6. The 5 X-ray Densities ● Black:↓density material ● White:↑density material C. SAMPLE RADIOGRAPHS NORMAL FINDINGS Figure 9. Abnormal Chest X-ray (Large Pulmonary Mass and Interstitial Disease) ● Large pulmonary mass and interstitial disease in right lung ○ Interstitial disease can be seen as a bright structure at the periphery PLAIN ABDOMINAL RADIOGRAPH Figure 7. Chest X-ray, PA view ● Radiographic anatomy: ○ Lung ○ Heart ○ Trachea ○ Diaphragm (seen in chest x-ray but not in KUB) ○ Costophrenic sulci (always check for fluid or pathologies in the pleura) ○ Soft tissues ○ Bones ● Expected findings: ○ Air in the lungs appears dark or black ○ Blood in the heart appears white ○ Bone (rib cage) appears bright or white Figure 10. Plain Abdominal Radiograph of a Patient with Pneumoperitoneum ● Air in the GIT (ascending colon) appears dark or black ● Bone (thoracolumbar spine) attenuates x-ray and appears bright or white ● Diaphragm must be included KUB X-RAY ● KUB: kidney, ureter, and bladder ● Similar to abdominal x-ray ○ Difference: diaphragm is included in an abdominal x-ray YL6:01.34 General Overview of Radiology 3 Active Recall Box 1. T/F: Conventional radiology is a cornerstone imaging technique because it is frequently requested. 2. Which view should you use to assess a lateral patellar dislocation? 3. T/F: A KUB X-ray can be done to best visualize the diaphragm? 4. T/F: Fat only appears as dark structures in ultrasound. Answers: 1T, 2 Sunrise view, 3F, 4F III. ULTRASONOGRAPHY Figure 11. KUB X-ray of Staghorn Calculi ● KUB x-ray shows radiopaque stones conforming to the kidney’s calyces ● Case of bilateral nephritis SKULL X-RAY ● Uses high-frequency sound waves ● Image created depends on the reflecting and absorbing properties of the different tissues ● Sound waves propagate better through fluid and soft tissues ● Sound transmission is blocked or scattered by air and calcium ○ Ultrasound is not used for air-containing structures or bones (for fractures, etc.) A. ULTRASOUND IMAGE PRODUCTION Figure 12. Skull X-ray ● Lucent abnormality in the frontal area of the skull ○ Lytic lesion of the skull: lysis of the bone ○ Lucent structure is less dense than the surrounding bone and is likely to be a mass/tumor PELVIS X-RAY Figure 14. Diagram of how an ultrasound image is produced 1. High-frequency sound waves goes through the body a. Created by the thickening of the piezoelectric crystals in the transducer due to short voltage spikes (1.27, 2026) b. The sound waves go through the processes of: i. Diffusion ii. Reflection iii. Refraction iv. Absorption 2. Once the sound waves reach the organ, each organ/structure has a very specific capability to attenuate sound waves a. This gives different signals, which return back to the transducer 3. From the transducer, the signals will be converted into an ultrasonic image B. PRINCIPLES OF INTERPRETATION Figure 13. Foreign Body Shown in a Pelvis X-Ray ● Tissues exhibit different capacities to attenuate sound waves ● Tissues appear as varying shades of gray, depending on density and thickness ● Male patient with a foreign body in the pelvis: ○ Visible penis ○ Narrow subpubic angle ○ Android shape pelvis YL6:01.34 General Overview of Radiology 4 C. TYPICAL APPEARANCE OF TISSUES Figure 15. Sample ultrasound image showing subcutaneous fat (F) and muscle (M) ● Skin appears smooth and bright ● Fat can be bright or dark ○ In the breast, the fat is usually darker ● Muscle is also dark ● Fluid is generally black Figure 18. Gallbladder with stone (displayed as a gray scale on a monitor) ● Take note of the posterior shadowing ○ Can indicate the structure is calcium-containing (lithiasis or stone) ● Bright: if object is highly reflective ○ E.g., gallstones ● Dark: if sound passes through freely ○ E.g., Fluids, such as bile Figure 16. Sample ultrasound image ● Tendons are typically bright ● Nerves are not normally seen, unless pathologic ● Bone appears as a bright line D. SAMPLE ULTRASOUND IMAGES Figure 19. Kidney X-ray and ultrasound ● In Figure 19, the patient is lying down ● Bright echoes: essential echo complex, which are the collecting structures ○ Calyces are filled with calcium ○ Casting a posterior shadow Figure 20. Ultrasound of the gallbladder showing biliary ascariasis Figure 17. Scrotal ultrasound, showing abnormalities (yellow arrow) ● Fat → usually white (omentum) ● Fluid → dark (hydrocele) ● Solid tissues → speckled pattern of tissue texture with blood vessels (testis) ● Lesions → displacement of vessels, mass effect, change in contour (hernia) YL6:01.34 General Overview of Radiology 5 E. DOPPLER ULTRASOUND ● Useful in obstetrics (pregnant women), children and vascular evaluation ● Limited by body habitus ○ Poor visualization of deep structures in obese individuals IV. COMPUTED TOMOGRAPHY (CT) ● Also known as computerized axial tomography (CAT) ● Uses the same technology as X-rays A. CT SCAN IMAGE PRODUCTION Figure 21. Doppler ultrasound procedure ● Rotating x-rays pass through the body ● Detectors collect the x-ray profiles ○ At the bottom ● Image is sent to computer for processing ● CT Image ○ CT Scan takes images axially ○ It can be reconstructed into a 3D view (i.e., sagittal, coronal) Figure 23. CT Scan Image Production Figure 22. Sample Doppler ultrasound images ● Useful adjunct ● Vascular applications: for blood vessels ● Estimates velocity of moving objects in the body, such as blood F. ULTRASOUND ADVANTAGES AND DISADVANTAGES Table 1. Advantages vs disadvantages of ultrasound Advantages Disadvantages ● No ionizing radiation ● Operator-dependent ○ Lesions can be left undetected depending on the operator’s skill with the probe ● Portable and can image in any plane ● Cannot image air-containing structures ● Real time ○ Good for mobile structures, guiding drainage or biopsy procedures ● Cannot penetrate through bone YL6:01.34 General Overview of Radiology Figure 24. CT Scan Image Production (Abdominal, Axial) B. PRINCIPLES OF INTERPRETATION ● Tissues exhibit different capacities to attenuate x-rays ● Dense structures in the body block the transmission of x-rays ○ Dense structures: metal and bone → white ▸ Metal is more dense than bone ○ Less dense: various structures of gray ○ Least dense: air → black 6 C. CT ADVANTAGES AND DISADVANTAGES Table 2. Advantages vs disadvantages of CT scan Advantages Figure 25. CT Scan with Attenuation differences (arrow points to mastoid air cells) Disadvantages Good contrast between tissues High-dose procedure (= 100 500 CXR) → Higher radiation than x-ray More sensitive to differences in density than plain films Recent barium studies obscure images of the abdomen and pelvis Not degraded by bowel gas Artifact caused by high-density metal in teeth and joint replacements may limit the diagnostic accuracy of neck and pelvic examinations D. SAMPLE CT IMAGES Figure 26. Cranial CT Scan ● Displayed on gray scale ○ More dense matter: white (bone) ○ Less dense matter: black (air, fat) ○ Soft tissues: varying shades of gray THE HOUNSFIELD UNIT Figure 28. Lower Abdominal CT Scan. Left (Axial). Right (Sagittal) ● Hounsfield unit (H): assigned CT numbers in the image to measure the relative density of a region of interest (ROI) ○ Tells us the nature of a particular structure ○ Higher number, higher density ● Relative radiodensity unit ○ Air: - 1000 HU (low density) ○ Fat: -60 to - 100 HU ○ Water: 0 HU ○ Soft tissue: +40 to +80 ○ Bone: +400 to +1000 (high density) ● Radiodensity assigned at standard temperature and pressure Figure 29. CT scan of the brain (Axial) Figure 27. CT Scan Attenuation, Density YL6:01.34 General Overview of Radiology Figure 30. Normal vs. Abnormal CT of the brain (Axial). Lesion is a glioblastoma 7 V. MAGNETIC RESONANCE IMAGING (MRI) A. MRI IMAGE PRODUCTION ● Produces images by means of magnetic fields and radio waves ● Tissues are differentiated by characteristic T1 and T2 relaxation times ● Use of contrast media is not essential to visualize vascular structure ● Problems with claustrophobia ● Contraindicated in patients with metallic implants CT SCAN VS. MRI ● Superior to MRI for evaluating calcified or ossified abnormalities of the musculoskeletal system ● Less expensive ● Faster study ● No problems with claustrophobia VI. NUCLEAR IMAGING A. BASIC PRINCIPLES Figure 31. Principles and components of MRI B. MRI SIGNAL INTENSITIES MRI Signal Intensities: WW2 Water is White on T2 ● Detection of the biodistribution of radiotracers that have been administered to the patient ○ Radiotracers are injected, swallowed or inhaled ○ There are specific radiotracers for specific organs ▸ Radiotracers will go to the organ of interest depending on their characteristics ● Provides physiologic and functional information on the presence or absence of disease B. NUCLEAR IMAGING ADVANTAGES AND DISADVANTAGES Table 3. MRI T1 vs MRI T2 Table 5. Advantages vs disadvantages of nuclear imaging T1 T2 ● Appears bright: ○ Fat (less bright on T2) ○ Blood (methemoglobin) ○ Proteinaceous material ○ Melanin ○ Gadolinium (MR contrast agent) ● Appears dark: ○ Calcium ○ Gas ○ Chronic hemorrhage (hemosiderin) ○ Mature fibrous tissue ● Appear dark: ○ Water ○ CSF ● Appear bright: ○ Water ○ CSF ● Good for delineating the normal anatomy ● Good for finding lesions ○ Appear brighter C. MRI ADVANTAGES AND DISADVANTAGES Advantages ● Provides functional information such as: ○ Rates of metabolism ○ Levels of various other chemical activity ● Poor anatomical resolution ○ Depicts physiologic processes, instead of showing anatomy and structure ● Less expensive than exploratory surgery ● Higher dose (15 to 200 CXR) ● May detect the early onset of disease before it is evident on other imaging tests such as CT or MRI ● Limited by availability of radionuclides Table 4. Advantages vs disadvantages of MRI Advantages ● Limited in demonstrating dense bone detail or calcifications ● Multiplanar imaging capability ● Long imaging times ○ May take ≥ 30 minutes ● Better anatomic detail ● Limited availability in some areas ● No ionizing radiation ● Expensive YL6:01.34 ● Patient needs to lie relatively still for long periods Disadvantages ● Outstanding soft tissue contrast General Overview of Radiology Disadvantages ● Time-consuming C. NUCLEAR IMAGING MODALITIES ● ● ● ● Bone scan or bone scintigraphy SPECT PET PET-CT SPECT ● Single Photon Emission Computed Tomography ● Shows how blood flows to tissues and organs 8 PET ● Positron Emission Tomography ● Measures important body functions ○ Blood flow ○ Oxygen use ○ Sugar (glucose) metabolism ● Help doctors evaluate how well organs and tissues are functioning ● Uptake of radiotracers are indicated by different colors US Echogenic, hyperechoic, high attenuation Hypoechoic, anechoic, low attenuation MRI Hyperintense Hypointense A. CONVENTIONAL RADIOGRAPHY (DENSITY) ● Opaque / dense / hazy: white ● Lucent: dark Figure 32. PET scan of patient with seizure Figure 34. CXR with (+) lucent density (left) and (+) opacity (right) SPECT vs. PET ● SPECT ○ Tracer stays in blood ○ Tracer is not absorbed by surrounding tissues ○ Limits images to areas where blood flow occurs ○ Cheaper ○ More readily available than PET scans B. ULTRASONOGRAPHY (ECHOES) ● Anechoic: no internal echoes (black) ● Hyperechoic/echogenic: bright echoes (white) ● Hypoechoic: dark echoes (gray to black) PET/CT ● Powerful in determining metastasis ● Combines anatomy and function knowledge ● Combined PET/CT scans ○ Pinpoint anatomic location of abnormal metabolic activity Figure 35. Ultrasonography: anechoic (left), hyperechoic (middle), hypoechoic (right) C. CT SCAN (DENSITY) ● Isodense (same as surrounding tissue) ● Hyperdense (bright) ● Hypodense (dark) Figure 36. Cranial CT showing different densities D. MRI (INTENSITY) ● Hyperintense (bright/white) ● Hypointense (dark) ● Isointense (same as surrounding tissue) Figure 33. PET/CT scan VII. TERMINOLOGIES ● Refers to signals of pathologic process relative to surrounding tissues Table 6. Terms used in each modality Modality White or Bright Black, Gray, or Dark X-ray Dense, opaque, bright, hazy Lucent, hypodense CT Dense, Hyperdense Hypodense YL6:01.34 General Overview of Radiology Figure 37. Cranial MRI (coronal section) showing different intensities 9 E. NUCLEAR IMAGING (INTENSITY) ● Hot spots ○ Areas of greater intensity ○ Large amounts of radiotracer accumulate ○ High level of chemical and metabolic activity ● Cold spots ○ Less intense areas ○ Indicate smaller concentration of radiotracer ○ Less chemical activity Figure 40. Plain skull x-ray with lucent/hypodense lesion Figure 38. Spinal column scan showing hot spots Active Recall Box 5. T/F: An advantage of CT Scan is that it is not degraded by bowel gas. 6. T/F: Cerebrospinal fluid appears bright on T1-weighted MRI. 7. T/F: A dark looking lesion on an MRI of the brain is classified as hypodense. Figure 41. Acoustic enhanced ultrasound of the breast with anechoic abnormality (simple breast cyst) Answers: 5T, 6F, 7F VIII. SAMPLE RADIOLOGIC IMAGES Figure 42. Ultrasound of the testis with anechoic cyst on left testicle Figure 39. X-ray of abdomen with an opaque/dense coin in ileocecal junction YL6:01.34 General Overview of Radiology Figure 43. Ultrasound of the gallbladder with hyperechoic gallstone (lower white arrow) 10 Figure 44. Ultrasound of thyroid with hypoechoic lesion (green arrow) and hyperechoic calcification (center of lesion) Figure 48. MRI of the brain with hyperintense lesion Figure 45. CT Scan of abdomen with isodense/hypodense structures on liver (pointed by white arrows) Figure 49. MRI of the brain with hypointense lesion Figure 50. Mammogram of the breast with abnormal left breast (equal density/high density of glandular tissues) Figure 46. CT Scan of chest with hyperdense mass in lungs (green arrow). Potentially an adenocarcinoma or carcinoma Figure 47. CT Scan of liver with contrast with hypodense structures (red arrows) Figure 51. PET-CT Scan YL6:01.34 General Overview of Radiology 11 7. 8. 9. 10. Figure 52. Bone scintigraphy of patient with prostate cancer (dark areas on pelvis) QUICK REVIEW QUESTIONS 1. 2. 3. 4. 5. 6. What is the most dense among the following? A. Pelvis B. Pacemaker C. Omentum D. Liver What part of the abdominal x-ray is excluded from the KUB? A. Pelvis B. Heart C. Diaphragm D. All of the above What is the main reason to see the diaphragm in an abdominal X-ray? A. To assess the condition of the kidneys in relation to the diaphragm B. To evaluate the patient's breathing rate C. To detect air outside the bowels D. To check for fractures in the ribs What does the term "radiologic right" mean in a chest X-ray? A. It refers to the patient's actual right side B. It signifies the left side of the patient C. It's the direction the X-ray machine is facing D. It points to the patient's back T/F: Air in the intestines is hyperintense when viewed in an x-ray. Bone attenuates x-ray, therefore it appears white. Air has low density. A. Only statement 1 is true B. Only statement 2 is true C. Both statements are true D. Both statements are false YL6:01.34 General Overview of Radiology 11. 12. 13. Doppler ultrasound studies are appropriate for evaluating and visualizing vascular structures, such as blood vessels. If a structure is highly reflective on an ultrasonic image, it usually indicates a structure filled with fluids. A. Only statement 1 is true B. Only statement 2 is true C. Both statements are true D. Both statements are false Among the following, what is a disadvantage of using ultrasound? A. It is considered safe for pregnant women and young children because it does not utilize ionizing radiation. B. It can show bone structures as well as radiographs and CT scans. C. It can take images in multiple planes. D. It can be used real time and can be used in biopsy and drainage procedures. What is the purpose of the Hounsfield unit (HU) in computed tomography (CT) imaging? A. To measure the size of a region of interest (ROI) B. To determine the temperature of a structure C. To assess the relative density of a region of interest D. To calculate the speed of sound in different tissues Which material has the highest relative radiodensity, as indicated by the Hounsfield unit (HU), in the given scale? A. Air B. Fat C. Water D. Soft tissue E. Bone T/F: Combined PET and SPECT modalities pinpoints the anatomic location of abnormal metabolic activity. T/F: Nuclear imaging is able to detect early onset of disease before it is evident on CT scan or MRI. Which of the following is true given the image below? A. This is an ultrasound of the thyroid with a hypoechoic lesion and hyperechoic calcification B. This is an ultrasound of the thyroid with a hyperechoic lesion and hypoechoic calcification C. This is an ultrasound of the breast with a hypoechoic lesion and hyperechoic calcification D. This is an ultrasound of the breast with a hyperechoic lesion and hypoechoic calcification 14. Which of the following is paired correctly? A. X-ray: Hyperechoic/Hypoechoic B. CT Scan: Opaque/Lucent C. MRI: Hyperintense/Hypointense D. None of the above 12 ANSWER KEY REFERENCES 1B, 2C, 3C, 4B, 5F, 6C, 7A, 8B, 9C, 10E, 11F, 12T, 13A, 14C RATIONALE 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. B. Pacemaker. From least dense to most dense: air, fat (e.g., omentum), soft tissue (e.g., liver), bone (e.g., pelvis), metal (e.g., pacemaker). C. Diaphragm. The KUB is similar to abdominal x-ray, but the diaphragm is included in an abdominal x-ray C. To detect air outside the bowels. In an abdominal X-ray, the presence of air outside the bowels, which can move up under the diaphragm, is a sign of potential bowel rupture. This is why it's important to see the diaphragm in abdominal X-rays. B. It signifies the left side of the patient. In a chest X-ray, the term "radiologic right" is used to avoid confusion because the X-ray image is like looking at the patient from the front. So, the side that's normally the patient's left becomes the "radiologic right." False. Air in the intestines is lucent or hypodense when viewed in an x-ray. C. Both statements are true. Bone has a higher density than air, so it attenuates more x-rays than air making bone appear white or hyperdense. The opposite is true for air. A. Only statement 1 is true. Statement 2 is false because bright echoes seen on ultrasonic images usually indicate structures that are filled with calcium, not bile. These bright structures are seen in gallstones, lithiasis, etc. B. It can show bone structures as well as radiographs and CT scans. Ultrasounds cannot show bone structures as well as x-rays and CT scans. Bones only show as straight white lines and ultrasound is not the modality of choice for bone fractures. C. To assess the relative density of a region of interest. The Hounsfield unit (HU) is a scale used in computed tomography (CT) imaging to measure the relative density of different tissues or structures within the body. The HU scale assigns specific CT numbers to various materials, which allows for the differentiation of tissues based on their density. E. Bone. Bone has the highest positive HU value range (+400 to +1000 HU), indicating its high relative density compared to the other materials listed. Therefore, bone has the highest relative radiodensity in this scale. False. It is the combination of PET and CT that pinpoints the anatomic location of abnormal metabolic activity. True. Nuclear imaging is able to detect early onset of disease before it is evident on CT scan or MRI. A. This is an ultrasound of the thyroid with a hypoechoic lesion and hyperechoic calcification. The image shows an ultrasound of the thyroid with a hypoechoic lesion (dark area) and a hyperechoic calcification (bright spot in the middle of lesion) C. MRI: Hyperintense/Hypointense. The correct pairing for the other modalities are X-ray: opaque/lucent and CT Scan: hyperdense/hypodense. YL6:01.34 General Overview of Radiology REQUIRED ● 💻 Koa-Sales, R. (2023, August 24). General Overview of Radiology [Lecture slides]. ● 📄 ASMPH 2026. 01.27: General Overview of Radiology by Koa-Sales, R., MD. SUPPLEMENTARY Concerns and Feedback form: http://bit.ly/YL6CFF2027 How’s My Transing? form: https://bit.ly/2027YL6HMT Mid-Semester Evaluation form: https://bit.ly/2027YL6MidSem End-of-Semester Evaluation form: https://bit.ly/2027YL6EndofSem Errata Points Trackers: https://bit.ly/YL62027EPT YL6 TransMap: https://bit.ly/2027YL6TransMap FREEDOM SPACE 13