Radiology Key Points
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| 1. Radiology Principles and Indications | There are four basic densities or appearances to observe on radiographs and CT images: air, which appears black; fat, which also appears black; soft tissues and organs, which appear gray; and metal, calcium, and bone, which appear white.
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| 1. Radiology Principles and Indications | Plain radiography images: produced by x-rays and radiographic film. CT images: x-rays, detectors, and computers. MR images: magnetic fields, radio-frequency waves, and computers. Ultrasound images: high-frequency sound waves, transducers, and computers.
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| 1. Radiology Principles and Indications | Sectional anatomy is the imaging of anatomy in multiple planes, including the axial plane (transverse or cross-sectional), the sagittal plane, and the coronal plane.
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| 1. Radiology Principles and Indications | A key to distinguishing an MRI from a CT image is that the fat in an MRI appears white.
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| 1. Radiology Principles and Indications | T1 MR images: excellent resolution -> best to obtain anatomic information. T2 MR images: better contrast than T1 images and cause water to light up -> best when looking for pathologies (they tend to contain a lot of water).
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| 1. Radiology Principles and Indications | The high resolution of CT makes it effective for imaging anatomy. MRI has high soft tissue contrast that makes it especially useful for soft tissue imaging.
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| 1. Radiology Principles and Indications | Type of contrast agents: barium sulfate, high and low osmolar iodinated compounds, ionic iodinated and nonionic (low osmolar) contrast media, air, gadolinium. Barium sulfate is better than water-soluble iodinated agents 2/2 less dense -> poorer contrast
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| 2. Chest | PA and lateral views are the routine standard chest radiographs.
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| 2. Chest | AP is the standard portable chest radiograph.
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| 2. Chest | If thoracic bone imaging is necessary, it is best to order the specific radiographs such as ribs, shoulders, or dorsal spine.
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| 2. Chest | Position chest radiographs on the viewbox with the patient’s labeled right side opposite the viewer’s left hand, and this generally applies to almost all other images.
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| 2. Chest | Develop a simple systematic approach for viewing chest radiographs to avoid errors of omission.
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| 2. Chest | The cardiac transverse diameter should not exceed 50% of thoracic cage transverse diameter. This is called the cardiothoracic ratio.
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| 2. Chest | Cardiac size estimation is most generally accomplished by gross eyeballing and becomes easier with experience.
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| 2. Chest | Cardiac size appears larger on the AP than the PA view because of magnification.
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| 2. Chest | The right atrium forms the convex right cardiac border, and the left ventricle forms the cardiac apex on AP or PA radiographs.
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| 2. Chest | On a chest radiograph, look for water densities as most chest radiographic pathology is water density.
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| 2. Chest | Excessive black density on a chest radiograph generally indicates too much air, and its location will help make the diagnosis.
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| 2. Chest | When two similar densities abut each other, it is virtually impossible to differentiate their borders on a radiograph. This is called the silhouette sign.
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| 3. Abdomen | Imaging evaluation of the abdomen usually begins with an AP supine abdominal radiograph. This is particularly helpful in evaluating the gas pattern.
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| 3. Abdomen | Small bowel obstruction is characterized by dilated small bowel proximally with collapsed colon and minimal rectal gas.
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| 3. Abdomen | In adynamic ileus, there is proportional dilatation of both small and large bowel with gas throughout the gut.
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| 3. Abdomen | If bowel perforation is suspected, it is critical to perform horizontal beam films (upright, decubitus, or cross-table lateral) inasmuch as 2 cc of free intraperitoneal air can be identified.
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| 3. Abdomen | Contrast studies of the gut remain a valuable method to detect intraluminal and mural diseases such as tumors, mucosal disease, and ulcerations. They are particularly useful in the small bowel, where endoscopy is technically difficult.
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| 3. Abdomen | Ultrasound is the primary imaging modality for obstetrics and useful for detecting gallstones, renal and gynecologic disease, and abdominal aortic abnormalities.
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| 3. Abdomen | Abdominal CT is the method of choice for detection, localization, and characterization of tumors.
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| 3. Abdomen | CT diagnosis of appendicitis is very reliable, with direct visualization of the inflamed appendix in most cases.
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| 3. Abdomen | CT without intravenous contrast material initially is the preferred method for evaluating suspected renal and ureteral stones.
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| 3. Abdomen | CT is the study of choice in evaluating the trauma patient.
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| 3. Abdomen | MRI is useful in a variety of special situations in the abdomen.
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| 4. Pediatric Imaging, Chest | In some babies, in utero lung fluid takes more than a few minutes to clear, resulting in transient tachypnea of the newborn. This appears on radiographs as pleural effusions and streaky densities. TTN should resolve within the first 24 hours after birth.
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| 4. Pediatric Imaging, Chest | TTN is indistinguishable on radiographs from early neonatal pneumonia.
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| 4. Pediatric Imaging, Chest | Best clue to diagnosing congestive heart failure in babies is a radiograph displaying a streaky density pattern in the lungs and cardiomegaly. Heart protrudes significantly beyond the visible airway on a lateral radiograph = enlarged of the heart
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| 4. Pediatric Imaging, Chest | Hyaline membrane disease displays four characteristic radiographic features: diffuse granularity, uniform disease, air bronchograms, and a relatively small lung volume.
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| 4. Pediatric Imaging, Chest | Generally, surgical conditions are unilateral amd will displace the mediastinum away from the more abnormal side.
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| 4. Pediatric Imaging, Chest | Radiographic features of cystic fibrosis include hyperexpanded lungs, mucoid impactions, very prominent hili, and peribronchial cuffing.
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| 4. Pediatric Imaging, Abdomen | In summary, the rules for evaluating an infant’s abdomen are different from those used for adults.
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| 4. Pediatric Imaging, Abdomen | The younger the child, the more discrepant the rules.
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| 4. Pediatric Imaging, Abdomen | Babies have a lot of air, and it is difficult to differentiate large from small bowel by plain film.
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| 4. Pediatric Imaging, Abdomen | Young children usually have congenital anomalies or atresias; slightly older children have manifestations of either congenital anomalies or heritable anomalies such as pyloric stenosis and malrotation.
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| 4. Pediatric Imaging, Abdomen | In children beyond 6 months, intussusception and appendicitis are the major clinical entities.
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| 4. Pediatric Imaging, Abdomen | In looking at abdominal films of children, remember that your odds are much better in diagnosing an unusual manifestation of a common disease (such as appendicitis) than in diagnosing a common manifestation of a rare disease.
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| 4. Pediatric Imaging, Abdomen | If you stick with the diagnosis and rules from this chapter, you will be right more often than you will be wrong.
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| 5. Musculoskeletal System | It is important to recognize sesamoid bones and ossicles as normal variants. Sesamoids are bones within a tendon. Ossicles are extra or supernumerary bones next to the skeleton and usually named after the neighboring bone.
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| 5. Musculoskeletal System | MRI is useful for injuries to the shoulder rotator cuff, knee ligaments and menisci, ankle ligaments, and Achilles tendon. CT is good for bone detail, fracture diagnosis, locating fracture fragments, and evaluating matrix formation in bone tumors.
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| 5. Musculoskeletal System | The Salter-Harris classification describes fractures around the physis, which is considered the weakest point in a growing bone.
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| 5. Musculoskeletal System | Because fractures and other abnormalities may not be visualized on all radiographic views, always insist on at least two views of an injured or diseased area that are 90 degrees to each other.
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| 5. Musculoskeletal System | Fractures may not be visible on the first radiographs but may become visible after time (7 days) because of bone resorption at the ends of the fracture fragments.
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| 5. Musculoskeletal System | A transverse lucent line at the base of the fifth metatarsal always represents a fracture, whereas the normal apophysis in this area is lateral and parallel to the long axis of the metatarsal.
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| 5. Musculoskeletal System | Osteoarthritis is the most common form of arthritis and often results from asymmetric cartilage wear.
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| 5. Musculoskeletal System | The radiographic features of osteoarthritis include irregular joint narrowing, sclerosis, absence of osteoporosis, and osteophyte formation.
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| 5. Musculoskeletal System | The radiographic features of rheumatoid arthritis include periarticular thickening, symmetric joint narrowing, marginal erosions, periarticular osteoporosis, and joint deformity.
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| 5. Musculoskeletal System | Metastatic cancer is the most common malignant bone tumor. The majority of metastatic lesions are osteolytic or radiolucent. Osteoblastic metastatic lesions most commonly are secondary to prostate and breast neoplasms.
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| 5. Musculoskeletal System | Multiple myeloma is the most common primary malignant bone tumor, and it originates in the bone marrow.
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| 5. Musculoskeletal System | Ewing’s sarcoma usually occurs in children and young adults. They may have a permeative type of lesion and an onion-skin-like periosteal reaction.
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| 5. Musculoskeletal System | Osteomyelitis and septic joints typically present with localized pain and fever. The radiographic features include bone and joint destruction, periosteal reaction, and occasionally, a soft tissue component.
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| 6. Spine and Pelvis | Basic observations on spine radiographs should include spinal alignment, the heights of the vertebral bodies and the intervertebral disc spaces, osseous density, presence of the pars interarticularis in the lumbar spine and the pedicles of each vertebra.
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| 6. Spine and Pelvis | An absent pedicle is abnormal and should make you suspicious of a destructive process such as primary and secondary bone neoplasms.
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| 6. Spine and Pelvis | Spine CT is good for bone detail, localization of fracture fragments and their relationship to the spinal canal and cord, and diagnosis of herniated intervertebral disc disease.
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| 6. Spine and Pelvis | Spine MRI is good for imaging disease processes that involve the bone marrow fat such as tumor and infection. MRI is also valuable for diagnosis and staging of herniated intervertebral disc disease and evaluating the spinal cord.
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| 6. Spine and Pelvis | Most congenital anomalies of the spine are asymptomatic.
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| 6. Spine and Pelvis | Hyperflexion injuries include teardrop fractures, posterior ligament injury, and facet locking. Locked facets commonly have associated spinal cord injury.
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| 6. Spine and Pelvis | Odontoid process fractures are frequent in the elderly and result from both hyperflexion and hyperextension injuries.
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| 6. Spine and Pelvis | Open-mouth AP radiographs and CT are useful tools for diagnosing odontoid fractures.
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| 6. Spine and Pelvis | A ring is rarely broken in only one location. At least two fractures are usually present in the pelvis.
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| 6. Spine and Pelvis | Acetabular fractures are evaluated by AP and oblique (Judet) views of the pelvis.
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| 6. Spine and Pelvis | Following an acetabular fracture, subsequent studies should closely evaluate for the presence of avascular necrosis in the femoral head.
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| 7. Brain | Computerized axial tomography (CAT), or computed tomography (CT), is the most commonly performed neuroimaging study in the United States. CT scans can depict the brain in horizontal planes that can be viewed at different levels.
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| 7. Brain | When assessing a CT scan for potential trauma, begin by looking for blood in the head outside the vascular system. Blood appears on CT initially as a white blob.
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| 7. Brain | Mass effect is a clue that pressure is impinging on an area of the brain. The best way to find significant mass effect is to look for asymmetry with displacement of the midline structures.
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| 7. Brain | Obliteration of the distinction between gray and white matter in the brain represents profound edema. Edema profound -> “bad black brain” -> poor outcome and is almost always caused by a limitation of oxygen in the brain.
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| 7. Brain | CT: acute strokes = dark edematous blotch obliterating the normal tissue density. MRI with inversion recovery or T2 weighting: damaged tissues = white (due to leakage of water from ischemic cells). Diffusion MRI = most sensitive imaging for acute stroke
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| 7. Brain | Tumors that are entirely enveloped in the brain tissues are usually of glial cell origin, with astrocytoma being the most common primary tumor.
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| 7. Brain | Complex anatomy in developmental brain anomalies is best shown with MRI.
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| 7. Brain | Physical abnormalities most often associated with congenital brain abnormalities include macrocephaly (big head), abnormal appearance of the face (particularly with midline abnormalities such as cleft palate), and meningocele.
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| 8. Head and Neck | CT is the imaging modality of choice in the evaluation of sinusitis and facial bone fractures.
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| 8. Head and Neck | Imaging features of sinusitis include (a) acute fluid collection of the sinus cavity, (b) mucosal thickening and (c) erosion of the bony wall of the sinus.
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| 8. Head and Neck | Tripod fractures involve the (a) lateral orbital wall, (b) maxillozygomatic suture and (c) zygomatic arch.
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| 8. Head and Neck | In Le Fort fractures, the facial bones are detached from the cranium by the fracture of the pterygoid plates.
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| 8. Head and Neck | In orbital blowout fractures, the inferior rectus muscle may be trapped by the fracture fragments of the orbital floor, requiring surgical release.
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| 8. Head and Neck | MR is the imaging modality of choice in evaluating head and neck tumors. A skullbase extension of the tumor requires MR imaging.
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| 8. Head and Neck | In adults, malignant mass lesions are common. In children, benign masses are more common.
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| 9. Nuclear Imaging | Nuclear imaging is performed using radiolabeled molecules injected into the body to create images of organ physiology.
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| 9. Nuclear Imaging | Ventilation-perfusion lung imaging plays an important role in the workup of patients with suspected PTE.
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| 9. Nuclear Imaging | Normal pulmonary perfusion essentially rules out the diagnosis of PTE.
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| 9. Nuclear Imaging | Visualization of the gallbladder with hepatobiliary scintigraphy almost always rules out the diagnosis of acute cholecystis.
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| 9. Nuclear Imaging | Bone pathology (e.g., metastases) causes increased bone hydroxyapatite formation, leading to increased uptake of the bone scan radiopharmaceutical.
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| 9. Nuclear Imaging | Bone scintigraphy is a sensitive test for detecting skeletal metastases, osteomyelitis, and fractures.
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| 9. Nuclear Imaging | Captopril renal imaging accurately detects hemodynamically significant renal artery stenosis in patients with renovascular hypertension.
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| 9. Nuclear Imaging | Myocardial stress perfusion imaging is an accurate technique for detecting coronary artery disease.
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| 9. Nuclear Imaging | PET imaging with FDG can detect many types of malignant tumors.
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| 10. Mammography | Approximately one in eight females in the United States will develop carcinoma of the breast at some time.
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| 10. Mammography | Mammograms must be interpreted by qualified radiologists. Mammograms of high quality are imperative.
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| 10. Mammography | A routine mammogram consists of mediolateral oblique and craniocaudal views.
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| 10. Mammography | Screening mammography, monthly breast self-examination, and annual breast examinations by a physician can improve the survival rate of breast cancer.
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| 10. Mammography | Mammographic findings suspect for malignancy include an irregularly outlined mass, skin retraction or thickening, architectural distortion (asymmetric compared to opposite breast), and/or a hypoechoic mass on ultrasonography.
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| 10. Mammography | Calcifications that are suspicious for malignancy include new calcifications, irregular punctate calcifications, pleomorphic calcifications, and small branching calcifications.
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| 10. Mammography | Ultrasonography is often useful in differentiating solid from cystic breast masses.
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| 11. Interventional Radiology | Interventional radiology is a specialty of medicine that provides patients diagnostic and therapeutic minimally invasive procedures using imaging guidance.
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| 11. Interventional Radiology | Written informed consent is necessary for most angiographic and interventional procedures. The benefits, risks, and possible complications must be discussed with the patient.
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| 11. Interventional Radiology | The Seldinger technique is a method for gaining vascular or visceral access using a needle, a guidewire, and a catheter.
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| 11. Interventional Radiology | Most arteriograms are performed via the common femoral artery, which should be punctured over the femoral head.
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| 11. Interventional Radiology | Iodinated contrast is nephrotoxic, particularly in diabetics and patients with preexisting renal impairment.
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| 11. Interventional Radiology | Computed tomography angiography (CTA) has superseded pulmonary angiography and ventilation/perfusion scintigraphy in the diagnosis of pulmonary embolism.
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| 11. Interventional Radiology | Most currently available IVC filters are permanent and are placed below the renal veins.
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| 11. Interventional Radiology | A positive nuclear medicine scan is helpful in patients with GI bleeding because it not only confirms the diagnosis but also directs the angiographer to the site of bleeding.
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| 11. Interventional Radiology | Arterial embolization is an important therapy for traumatic vascular injury, gastrointestinal bleeding, uterine fibroids, and certain oncology tumors.
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