Diagnostic Imaging: Introduction

Contents

1. Conventional Radiography 2. Computed Tomography3. Ultrasonography4. Magnetic Resonance Imaging5. Nuclear Medicine

Conventional Radiography

a. Fluoroscopy b. Mammography c. Contrast Studies

Contrast Studies Barium suspensions Intravenous urography (IVU) Hysterosalpingography Angiography myelography fistulography sialography galactography cholangiography

• discovery of x-rays by Roentgen.• The bones appear white on the developed

plate, in contrast to the surrounding darker appearing flesh.

• degree of transparency is based on the density of the material.

classification of radiologic subspecialties

a) Organ based include musculoskeletal, breast, neurologic, abdominal, gastrointestinal, thoracic, and genitourinary imaging. (Chest/Bones & Joints / Abdomen / Head and Spine)

b) Modality based include Ultrasound, PET, and MR imaging

c) Subspecialty fields include pediatric imaging and women's imaging.

Conventional Radiography

• Conventional radiography remains a fundamental tool in the detection and diagnosis of disease presenting in the chest , abdomen, pelvis, breasts, and bones.

Standard posteroanterior chest X-ray. A tumor (T) is seen at the left hilum.

Fluoroscopy• Procedure—after administration of the dye

continuous beam of x-rays to evaluate dynamic processes, such as bowel peristalsis and diaphragmatic excursion,

• Indicationsa. evaluation of the upper and lower gastrointestinal

tract (e.g., barium enema)b. spinal cord in the case of a lumbar puncture or

myelogram.c. Angiographyd. feeding tube or drainage catheter placement.

Mammography

• Used for optimal detection of breast lesions, particularly early breast carcinoma.

• Breast lesions +ve

US-guided core biopsy or fine-needle aspiration (FNAC)

Contrast Studies• Decreased natural contrast between adjacent

structures of roughly similar radiographic density mandates the use of contrast material.

• Contrast media are commonly utilized for the evaluation of

a. GIT , Urinary tract, vascular system;b. biliary tree for carcinoma or obstruction, c. spinal canal, fistulous tracts arising from abscesses, d. uterine cavity and fallopian tubes for uterine

anomalies and tubal patency, respectively (hysterosalpingography).

Iodinated contrast agents• are water soluble • classified in several ways, ionic/nonionic, monomeric/dimeric, or

hyperosmolar/hypo-osmolar. • Side effects, while uncommon, encompass a spectrum, ranging

from mild reactions (flushing, tachycardia, and metallic taste in the mouth) to life-threatening effects (hypotension, severe bronchospasm, cardiac arrest).

• use of low-osmolality contrast agents is advocated, because these agents have a significantly lower incidence of drug reactions.

• Uses of Water-soluble contrast agents—a. gastrointestinal tract for suspected perforation, b. prior to surgical procedures, c. for contraindications to barium suspensions.

Contrast Studies Barium suspensions Intravenous urography (IVU) Hysterosalpingography Angiography myelography fistulography sialography galactography cholangiography

Barium suspensions

• Used for the standard upper gastrointestinal (UGI) series and for evaluation of the small bowel and colon.

• Both single- and double-contrast techniques can be performed in an UGI series after oral administration of a barium suspension or during a barium enema, following rectally administered barium .

• In the single-contrast study, only a barium suspension is used, whereas double-contrast studies use both barium and air to delineate mucosal irregularities and superficially located lesions.

A single-contrast retrograde colonic enema demonstrates an annular lesion

representing a cecal carcinoma (arrows)

Intravenous urography (IVU)• most common contrast study of the urinary tract. • After injection of contrast material into a peripheral vein,

sequential filming of the kidneys is performed , typically 1–3 minutes postinjection, as well as during contrast excretion into the renal collecting system and ureters (pyelographic phase, typically 3–10 minutes).

• Primary indications for this study include hematuria, urinary tract calculi, ureteral obstruction, and evaluation of a suspected congenital anomaly.

• Nonenhanced helical CT is rapidly superceding the standard IVU examination in cases of stone disease and ureteral obstruction.

• However, IVU remains the procedure of choice for evaluation of suspected uroepithelial neoplasms, such as transitional cell carcinoma, because it more sensitively detects subtle mucosal irregularities.

• Retrograde studies of the renal collecting system (retrograde pyelography), ureter (retrograde ureterography), and bladder (cystography)

• performed by direct instillation of water-soluble contrast material into the urinary bladder.

• These studies are typically performed for evaluation of vesicoureteral reflux, calculi, or tumor.

An AP film from an intravenous urogram taken at 10 minutes in a pt. with a proximal Lt ureteral calculus (arrow) and associated

left collecting system dilatation. The right collecting system is normal, and the right ureter (arrowheads),bladder are seen.

Hysterosalpingography• radiographic method for evaluation of the

endometrial cavity and the fallopian tubes.• Procedure-- direct instillation of water-soluble

contrast material into the cervical canal. • Indications: a. primary or secondary infertility work-up, b. detection of suspected uterine anomalies, c. assessment of tubal patency d. determination of the location of a uterine

leiomyoma within the endometrial cavity.

Angiography• the study of the vascular system• Procedure --injection of water-soluble contrast media intra-

arterially (or intravenously, for venous studies) through a percutaneously placed catheter under fluoroscopic guidance.

• Types: peripheral angiography, coronary angiography, thoracic/abdominal aortography, pulmonary angiography, cerebral angiography, and superior/inferior venocavography.

• Common applications include i. assessment of vascular disease (atherosclerosis, aneurysm,

vasculitis), ii. prior to therapeutic interventions (stent placement), iii. evaluation for pulmonary embolus.

Thoracic aortography

• is typically performed for the evaluation of suspected traumatic injury, dissection, aneurysm, vasculitis, thromboembolic disease, tumors, arteriovenous malformations (AVMs).

• CT angiography and MR angiography replaced conventional angiographic studies .

• Coronary angiographic studies identify areas of stenosis or occlusion involving the coronary arteries.

An aortogram demonstrates transection (arrow) of the aortic arch at the aortic isthmus extending about 4 cm below.

• In patients suspected of having a pulmonary embolus, pulmonary angiography may be performed.

• This procedure is generally used i. when the results of a ventilation-perfusion (V/Q)

scan or pulmonary CT angiography are equivocal ii. when a low-probability V/Q scan is obtained in

the presence of continued high clinical suspicion.

• myelography for evaluation of spinal cord compression.

• fistulography for detection of epithelialized tracts arising from an inflammatory, infectious, or neoplastic process.

• sialography for the assessment of ductal obstruction or tumor involving the salivary glands.

• galactography for detection of masses within large breast ducts .

• cholangiography for detection of biliary ductal masses or strictures.

Computed Tomography

Computed Tomography

• high-resolution CT• commonly used for evaluation of diffuse

interstitial lung disease or detection of pulmonary nodules.

• contrast resolution of vascular structures, organs, or hypervascular neoplasms can be enhanced following intravenous infusion of water-soluble contrast media.

Contrast-enhanced CT image of the upper abdomen demonstrates two low-attenuation

areas (M) confirmed as multiple hepatic metastases from gastrointestinal stromal tumor.

CT Angiography• Procedure-- intravenous administration of iodinated

contrast material. Using a MDCT scanner, images are acquired.

• CT angiography has become an important tool for i. assessment of the abdominal and iliac arteries,ii. the thoracic aorta, the pulmonary arteries, iii.and the extra- and intracranial carotid circulation.• Exquisite anatomic detail of both intra- and

extraluminal structures is revealed using this technique, including detection of intimal calcification and mural thrombosis.

CT Colonography

• CT colonography (virtual colonoscopy)• used primarily in the detection and

characterization of colonic polyps• These images display the mucosal surface of

the colon and internal density of the detected lesions;

• They also directly demonstrate the bowel wall and extracolonic abdominal and pelvic structures.

Ultrasonography

• noninvasive imaging technique that uses high-frequency sound waves.

• Limitations: a. operator-dependent nature, b.variable visualization of midline abdominal

organs (pancreas) or vasculature when obscured by overlying bowel gas

c. inability of sound waves to penetrate gas or bone.

Ultrasonography-Applications

• abdomen [liver, gallbladder, pancreas, kidneys], • pelvis (female reproductive organs), • fetus (routine fetal surveys for detection of anomalies), • vascular system (aneurysms, arteriovenous

communications, deep-venous thrombosis), • testicles (tumor, torsion, infection), • pediatric brain (hemorrhage, congenital

malformations), • breast, and • chest (size and location of pleural fluid collections).

• ultrasound-guided interventions –used fora. lesion biopsy, b.abscess drainage, and c. radiofrequency ablation.

A transverse ultrasound image of the gallbladder demonstrates a gallstone (arrow)

with the characteristic distal acoustic shadowing (S) because sound waves cannot penetrate the

gallstone.

Doppler ultrasound

• It is used to calculate the corresponding flow velocities, which reflects the flow pattern within the vessel.

• Color flow Doppler assigns colors (blue and red) to structures according to their motion toward or away from transducers.

• This information can be superimposed on a gray-scale image.

• Endoluminal sonography is used to image structures beyond the lumen of the hollow viscus.

• It is accurate in local staging of cancer and in detecting small lesions that may not be visualized with other imaging modalities.

• Applications:a. GI applications include quantification of the size and wall thickness

of esophageal carcinoma or varices. Eg. Upper GI endoscopy and colonoscopy.

b. Transrectal USG is performed for evaluation of the prostate. c. Genitourinary (GU) applications include examination of the severity

and length of ureteral strictures, diagnosis of upper tract neoplasms and urethral diverticula, identification of submucosal calculi.

d. The uterus, adnexa, and routine fetal examinations by using a transvaginal probe in the presence of an empty bladder.

e. Sonohysterography, an ultrasound-guided procedure, requires instillation of a sterile saline solution into the uterine cavity following cannulation for evaluation of endometrial masses or other abnormalities.

f. Transesophageal echocardiography is used for evaluating cardiovascular abnormalities after placement of a probe into the esophagus.

g. Three-dimensional ultrasound (3D-US) is widely used in obstetrics and vascular imaging.

i. 3D-US is used to quantify the volume of organs and pathology. ii. It has been used predominantly in obstetrics for studying normal

embryonic and/or fetal development and iii. for detecting specific congenital anomalies in a fetus at risk given a

known family history.

Magnetic Resonance Imaging

• In MR imaging, a pulsed radio-frequency (rf) beam is used in the presence of a strong main magnetic field to generate high-quality images of the body.

• Images can be acquired in virtually any plane, although sagittal, coronal, and axial images are commonly obtained.

• The most commonly used, clinically approved contrast for MR imaging is a paramagnetic agent (atoms with unpaired electrons in their outer shells) containing gadolinium, termed gadolinium dimeglumine.

MR imaging--Indications

• neurologic indications, including brain tumors , acute ischemia, infection, and congenital abnormalities.

• non-neurologic indications, namely, spine, musculoskeletal, cardiac, hepatic, biliary, pancreatic, adrenal, renal, breast, and female pelvis applications.

• Spine MR studies are useful for evaluating degenerative changes, disk herniation, infection, metastatic disease, or congenital abnormalities.

• Cardiac studies are performed to identify congenital anomalies and complex malformations (malpositioning of great vessels and/or cardiac chambers).

MR imaging--Indications

• Common musculoskeletal applications involve the knee, shoulder, and hip.

• The primary indication for the knee is the assessment of the menisci and ligaments following internal derangement.

• Rotator cuff tear is the most typical shoulder indication.

MR imaging--Indications• Abdomen -- hepatic MR imaging studies are often used to

diagnose atypical presentations of liver lesions, metastatic diseases, or hepatocellular carcinoma.

• Adrenal studies are performed primarily to distinguish adrenal adenomas from metastatic disease.

• Atypical renal masses, found incidentally on USG or CT, can often be better characterized on MR imaging.

• Breast MR imaging is predominantly utilized for detection and evaluation of ruptured implants, and to detect the breast cancers.

• Female pelvis --diagnosis and characterization of cervical and endometrial carcinomas, as well as adnexal lesions.

A midline sagittal T1-weighted contrast-enhanced MR image depicts a large tumor

(T) in the region of the pineal gland.

MR imaging--contraindications

• patients with metal implants or foreign bodies eg. intracranial aneurysm clips, intraorbital metallic foci, cardiac pacemakers, or specific types of cardiac valves.

• MR imaging may also be contraindicated for claustrophobic or uncooperative patients who may not respond to conscious sedation protocols.

Diffusion-weighted MRI

• It is exquisitely sensitive to the microscopic molecular motion of water, demonstrating areas of limited (restricted) intracellular diffusion following an acute ischemic event.

• This sequence is routinely utilized in clinical neuroimaging protocols, but is nonspecific for pathology.

• diffusion changes similar to that seen with acute ischemia can be observed with infection and some tumors.

3D contrast-enhanced magnetic resonance angiography (MR angiography)

• It is used for noninvasive assessment of many vascular abnormalities, including aneurysms, dissection, vessel anomalies, and coarctation.

Magnetic resonance cholangiopancreatography (MRCP)

• It is used to evaluate choledocholithiasis, retained gallstones, pancreatobiliary neoplasms, strictures, primary sclerosing cholangitis, and chronic pancreatitis.

• ERCP is generally reserved for therapeutic purposes, such as stent placement, stone extraction, or stricture dilatation.

Nuclear Medicine

• Nuclear medicine studies are performed by administering a radiopharmaceutical to the patient and subsequently recording its distribution in the body over a defined period of time.

• In general, these studies are very sensitive, but relatively nonspecific, in the detection of pathophysiology.

• Correlation with pertinent clinical history, physical findings, laboratory data, and other diagnostic imaging procedures is, therefore, essential to render an accurate interpretation and for maximizing clinical benefits to both the patient and ordering physician.

• radiopharmaceuticals typically consist of two components:

(1)the main component, which is the compound distributed to various organs by a number of physiologic mechanisms, and

(2)the radionuclide tagged to this component, which emits gamma rays, permitting detection of the compound in the body.

Types of Nuclear studies

• Single photon emission computed tomography (SPECT)

• Positron emission tomography• new developments in PET technology include

the use of combined PET/CT imaging devices

• Advantages of both SPECT and PET include i. ability to map the distribution of the

radiopharmaceutical in three dimensions, ii. quantifying uptakeiii.ability to generate cinematic displays of the

organ imaged.

Common nuclear medicine procedures include

A. cardiac studies for evaluation of myocardial perfusion and/or ventricular function;

B. skeletal studies for detection of early bone metastases and primary bone neoplasms;

C. renograms and renal scans for assessment of renal function and morphologic defects (e.g., pyelonephritis);

D. ventilation–perfusion studies for identification of suspected pulmonary emboli; and

E. PET studies for tumor diagnosis and staging (e.g., lung, colorectal, breast, lymphoma, melanoma), as well as for evaluation of neurodegenerative disorders (dementia), brain tumor recurrence, and myocardial viability.

• less commonly performed nuclear medicine studies include

a. diagnostic thyroid studies for evaluation of nodules and following iodine-131 therapy for hyperthyroidism and thyroid cancer,

b. hepatobiliary studies for determination of acute cholecystitis and bile duct patency,

c. brain imaging for assessment of brain death and dementia,

d. white blood cell studies for detection of infectious or inflammatory processes,

e.gastrointestinal bleeding studies for detection and localization of small bleeds,

f. lymphoscintigraphy to identify sentinel lymph nodes for surgery, and

g. parathyroid scans to identify adenomas and hyperplasia.

A 99mTc-MDP bone scan in the anterior and posterior projections demonstrates multiple foci of increased radiopharmaceutical

accumulation (spine, ribs, pelvis, and left clavicle) with the typical appearance of bone metastases.