UNDER DEVELOPMENT

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achandr@lumc.edu

This module is created to guide third year medical students on how to look at the imaging studies.

Arcot J. Chandrasekhar, M.D.

CXR

What are the views of chest taken in CXR?

• PA view and left lateral chest are the routine views.
• In these views the heart is closest to the cassette. As a result the heart is sharp and there is least distortion of its size.

What are the quality characteristics we should evaluate first?

• PA vs AP: In AP film the heart appears larger, mediastinum is widened, pleural effusion layers in the back of thorax, diaphragms are high and the vessel size is the same between upper and lower lung fields.
• Rotation: Mediastinal position changes based on to which side the film is rotated.
• Penetration: Small lesions and interstitial disease can be missed in over penetrated films. Lung fields will appear dark and can be mistaken for emphysema.
• Inspiration: Basal lungs can appear congested with incomplete inspiration. Mediastinum can appear wider.

What are the densities that you can recognize in CXR?

Increasing densities in the following order:

• Air: black. Lung fields are black with white branching vessels
• Fat: gray. You can see fat in neck, axilla and along the chest wall
• Liquid: white. Heart, mediastinum and pulmonary vasculature appear white
• Bone: dense white
• Contrast: dense white
• Metal: dense white

You can distinguish bone, contrast and metal easily.

Systematic reading of CXR, one option:

• A (airway) position of mediastinum
• B (bones)
• C (cardiac) Heart size and silhouette of heart
• D (diaphragm) position of diaphragm
• E (everything else) Breast, abdomen, axilla, neck, chest wall, tubes and lines when present.
• L (lungs)
• M (mediastinum)
• P (pleura) Costophrenic angle

Abdomen 4 views are done for evaluation of acute abdomen.

What are the four views of abdomen?

• Upright chest: best view to look for air under diaphragm. Basal lung disease can sometimes present with abdominal pain.
• Upright abdomen: air under diaphragm, air fluid levels
• Supine abdomen: look at organs, calcifications and location of dilated bowel, air in rectum.
• Left lateral decubitus: sick patients who cannot stand upright useful to look for air between liver and chest wall.

What are the items you should evaluate in the four views of abdomen?

• Air (bowel, peritoneum)
• Calcifications
• Soft tissues
• Bones

What are the characteristic of normal bowel gas?

• Stomach, Small bowel, and Colon can be seen normally.
• Small bowel is normal up to 3 cms in width, with conniventes, is centrally located with some air fluid levels.
• Large bowel is normal up to 6 cms in width, peripherally located in abdomen with haustra. You can recognize large bowel by the presence of feces.

How do you distinguish small bowel obstruction from large bowel obstruction?

There is always collapse of bowel beyond complete obstruction.

• Small bowel obstruction: Dilated small bowel (larger than 3 cms) is centrally located with air fluid levels. They tend to be stacked up in small bowel obstruction. There is collapse of large bowel.
• In large bowel obstruction, colon proximal to obstruction is dilated (larger than 6 cms) and colon beyond the obstruction is collapsed. There will be no air in the rectum. If the ileocecal valve is incompetent, small bowel will also be dilated.

How do you determine that it is ileus?

• Ileus can be localized, next to inflammatory mass or diffuse as in post-operative state.
• In diffuse ileus, stomach, small bowel and large bowel are dilated. None of the bowel is collapsed as in obstructive bowel. There is air in the rectum.

 How do you recognize air in the peritoneum?

• Air is best detected under the diaphragm in upright and left lateral decubitus films.
• Double wall sign.
• Air in the peritoneum is most commonly due to perforated bowel.

What are the calcifications that can be encountered in abdomen?

• GB: In RUQ anteriorly located.
• Kidney: over the renal area located posteriorly.
• Ureter: along the lateral margin of psoas.
• Bladder: in midline over supra pubic region
• Prostate
• Aorta: Midline anterior to vertebra
• Vessels:
• phleboliths: multiple small calcified lesions with central hole most common in pelvis.
• Pancreas: across left to right over L2-3 in upper abdomen.
• Liver: granulomas or masses
• Spleen: granulomas
• Uterus: calcified fibroid.
• Masses.

What are the soft tissues that you should evaluate?

• Liver
• Spleen
• Kidney: left kidney higher than right kidney
• Psoas: loss of psoas shadow alerts one to retroperitoneal disease.
• Bladder: in midline pelvis
• Fat: streaking, abscess

What are the bones that you should evaluate in the four views of abdomen?

• Ribs
• Spine
• Pelvis
• Head and neck of femur

Plain Film Spine

What are the views taken for evaluation of lumbar spine for back ache?

• AP
• Lateral views

What findings should we look for at the spinal column?

• Kyphosis
• Scoliosis
• Alignment of vertebra

What do you look for in each vertebra?

• Height, similarity with others
• Shape
• Displacement

What do you look for in the inter vertebral space / cartilage ?

• Narrowing or obliteration
• Shape

What do you look for in the retroperitoneum?

• Kidney
• Pancreas
• Aorta

MRI Head

What are the views taken with MR?

• Axial, Sagittal and coronal views: This is one of the advantages of MR over CT.

What are sequences in MR?

There are various protocols used to obtain MR images, based on what we are looking for.

• T1 wtd image
  • T1 wtd image with contrast
• T2 wtd image
  • Flair
  • Diffusion wtd image
  • Fat suppression
  • Perfusion wtd image

How do you identify tissues in MR?

They are expressed as intensities.

They vary based on whether it is T1 wtd image or T2 wtd image.

Look at CSF. It is bright in T2 wtd image and dark in T1 wtd image.

In T1 wtd image

• Air:     
• Clear fluid: hypo intense / Dark  / CSF
• Acute hemorrhage      
• Fat:     hyper intense / bright  / scalp fat    
• Tissues:      
• Bone:  
• Contrast:    

In T2 wtd image

• Air:   
• Clear fluid:   hyper intense / Bright / CSF
• Acute hemorrhage:   
• Fat:    hyper intense / bright / scalp fat    
• Tissues:      
• Bone:  hypo intense / Dark  / skull

Look at non contrast T1 wtd image  and with contrast  T1 wtd image as a pair.

• Normal brain does not enhance with contrast.
• Contrast enhancement is seen with all pathological lesions.
• It is the enhancement pattern most useful in the differential.
• No contrast with T2 wtd images

CT Head

What are the sequences with CT scan head

• Non contrast
• With contrast

What are the views?

• Only axial views unlike MRI
• You can obtain reconstructed images by request

How do tissues appear in CT?

They are recognized as densities similar to plain x-rays.

Density is expressed as Hounsfield units

In the order of increasing density

• Air:        HU, Black, Sinuses
• Clear fluid:       HU, Dark, CSF
• Fat:          HU, Dark gray
• Tissues:       HU, Gray, White and Gray matter
• Bone:       HU, White, Skull
• Contrast:       HU, Dense white, in vessels and tissues
• Metal:           HU, Dense white

Look at non contrast CT and with contrast CT as a pair.

• Normal brain does not enhance with contrast.
• Contrast enhancement is seen with all pathological lesions.
• It is the enhancement pattern most useful in the differential.

CT Sinuses

What is scout film?

• Scout film shows you the section, the film represents

What are the views of sinuses x-ray?

• Sagittal
• Coronal
• Axial

How to tell the sides?

• Imagine that you are looking at the face of the patient.

Name the sinuses?

• Maxillary sinus
• Ethmoid sinus
• Sphenoid sinus
• Frontal sinus

Describe a normal sinus.

• Sinuses are air filled and appear dark.
• It is lined by thin mucous membrane.
• The drainage site is open.

When is sinus abnormal?

• Mucosal thickening
• Filled with fluid, gray or white.
• Filled with mass
• Erosion of bones

What are the adjacent structures to which infection can spread to?

• Maxillary sinus: to teeth, to orbit
• Ethmoid sinus: to orbit
• Sphenoid sinus: base of skull and brain
• Frontal sinus: brain

CT and MR Spine

What views are taken with CT?

• Axial view

What views are taken with MR?

• Sagittal view
• Axial view

What is CT good for?

• Good for evaluation of vertebra.

What is MR good for?

• evaluation of spinal cord
• evaluation of disc
• evaluation of tumors

CT Chest

What are the sequences taken with CT chest

• Non contrast CT
• With GI contrast
• With IV contrast

What are the views taken in CT?

• Scout film
• Axial sections
• You can obtain reconstructed images on request.

How do tissues appear in CT?

Tissue appear similarly in plain x-ray and CT.

Hounsfield units apply to CT.

Air -1000 H.U, Fat -10-100 H.U, Clear fluid 0 H.U, Bone + 1000 H.U

Hounsfield Units: Increasing densities representing tissues

1. Air: -1000
2. Lung: -700
3. Soft Tissue: -300 to -100
4. Fat: -50
5. Water: 0
6. CSF: +15
7. Blood: +30 to +45
8. Muscle: +40
9. Calculus: +100 to +400
10. Bone: +1000 (up to +3000 for dense bone)

Air is dark and bone is bright, with the rest of the tissues in between (shades of gray) in appearance in that order.

They are recognized as densities similar to plain x-rays.

Density is expressed as Hounsfield units

In the order of increasing density

• Air:        HU, / Black /  Lungs
• Fluid:       HU, / hyper dense / White./ blood vessels
• Fat:          HU/ hypo dense / Dark gray / neck, axilla, chest wall
• Tissues:       HU / Gray white / Heart, mediastinum
• Bone:       HU / hyper dense / White / Ribs, sternum, spine
• Contrast:       HU / hyper dense /  white / Vessels, GI tract
• Metal:           HU, / hyper dense / white

CT Abdomen

What are the sequences taken with CT abdomen?

• Non contrast CT
• With GI contrast
• With IV contrast

What are the views taken in CT abdomen?

• Scout film
• Axial sections
• You can obtain reconstructed images on request.

How do tissues appear in CT abdomen?

They are recognized as densities similar to plain x-rays.

Density is expressed as Hounsfield units

In the order of increasing density

• Air:        HU, / Black /  Bowel
• Fluid:       HU, / hyper dense / White./ gall bladder, urinary bladder
• Fat:          HU/ hypo dense / Dark gray / omental fat
• Tissues:       HU / Gray white / liver, spleen, kidney
• Bone:       HU / hyper dense / White / Ribs, spine, pelvis
• Contrast:       HU / hyper dense /  white / Vessels, GI tract
• Metal:           HU, / hyper dense / white

Mammogram

What is the difference between diagnostic and screening mammogram?

• Diagnostic mammogram takes specific views of suspected lesions in the screening mammogram.
• They are also done for biopsy of suspected lesions.

What are the views taken in mammogram study

• LAO
• RAO

What is the difference between young woman's breast and older women's breast in mammogram?

•  Young women have abundant mammary glands. Mammary gland is dense.
• As women age, mammary glands gets replaced with fat. Fat is dark. Cancer is recognized better in fat, as dark fat provides good contrast.

What are the structures you evaluate in reading a mammogram? Systematic evaluation.

• Symmetry. Some asymmetry is normal.
• Normal mammary gland is dense. Young women have abundant mammary glands.
• Fat: As women age mammary glands gets replaced with fat. Cancer is recognized better in fat, as dark fat provides contrast.
• Nodes: Small axillary lymph nodes can be seen normally. If they are larger than 3 cms we should be concerned.
• Calcification is commonly seen in normal breast. Cluster of micro calcification is concern for malignancy.
• Nipple: Retracted nipple is one of the findings of cancer breast.
• Skin: Edema and retraction are abnormal.
• Skin Markers are placed when the technician notes a skin lesion, to ensure that they are not mistaken for a lesion in the breast.

HIDA Scan

A HIDA scan is a nuclear medicine procedure and stands for hepatobiliary iminodiacetic acid scan. HIDA scan is conducted after an ultrasound examination of the abdomen for right upper quadrant pain. If the ultrasound examination fails to demonstrate gall stones or obstruction to biliary tree, to establish a cause of right upper quadrant pain, HIDA scan can be performed. HIDA scans are not the first imaging study for this purpose due to their increased cost, use of radioactive tracer and the duration required for the test.

The injected radioactive tracer is taken up by the bile-producing cells (reticulo-endothelial system)  and travels with the bile from liver into gallbladder through cystic duct and through common bile duct to small intestine. A gamma camera takes pictures of the tracer as it moves through body. Each picture takes about a minute. The HIDA scan is stopped when the radioactive tracer enters small intestine. This typically takes about an hour. The gamma camera creates pictures of liver, gallbladder, bile ducts and small intestine. In addition we measure the rate at which bile is released by gallbladder (gallbladder ejection fraction) after a fatty meal.

What is the purpose of doing HIDA scan?

Object of the scan is to follow the isotope secreted by liver along the biliary pathway to bowel.

What is the normal duration of performing HIDA scan?

Each image is timed in minutes since the injection of the isotope. Duration of the study can range from 30 minutes 4 hours. If completed in 60 to 90 minutes, most likely the study is normal.

What is the sequence of isotope uptake in biliary path?

• Liver uptake is promptly seen in few minutes.
• GB stores the bile with the isotope and  empties into the common bile duct through the cystic duct.
• You can recognize the common hepatic duct joining the cystic duct to form the common bile duct.
• Duodenum: The isotope is dumped into the second part of duodenum from the common bile duct. You can recognize duodenum by its U shape.

How do you interpret HIDA Scan?

A normal result means that the gallbladder is visualized within 1 hour of the injection and the tracer is in the small intestine.  

GB not visualized:  If the gallbladder is not visualized within 4 hours after the injection it indicates that there is either cholecystitis or cystic duct obstruction.  HIDA scan for acute cholecystitis has a sensitivity of 97%, Specificity of 94%.

Tracer not visualized in intestines means common bile duct obstruction. If the radioactive tracer moves through bile ducts very slowly, this may indicate a blockage or obstruction. Or it may indicate a problem in liver. .

If the radioactive tracer is found outside of biliary system it indicates a leak.

Bone Scan

Bone Mineral Density (BMD)

A DXA test measures bone mineral density and compares it to that of an established norm or standard to give a score. BMD test is the best way to identify patients with osteoporosis, determine risk factors for fractures and measure response to osteoporosis treatment.

What is a T-score?

T-SCORE = the number of standard deviations the bone mineral density measurement is above or below the YOUNG (30 year old)-NORMAL MEAN bone mineral density.Patients BMD - Young adult  Mean BMD / Standard deviation of young adult BMD.

What is a Z-score?

Z-SCORE = the number of standard deviations the measurement is above or below the AGE -MATCHED MEAN bone mineral density.Patients BMD -  Peer age group Mean BMD  / Standard deviation of peer age group BMD

Which bones do you measure the mineral density?

• Spine and Neck of femur (hip)

How do you use T in clinical decision? What are the ranges for normal, osteoporosis and osteomalacia?

A bone mineral density more than 2.5 standard deviations below the mean for a young healthy adult white woman identifies 30 percent of all postmenopausal women as having osteoporosis; half of these women will already have had a fracture.

• -1 to +1 is normal range
• -1 to -2.5 is osteopenia
• -2.5 is osteoporosis

The hip T-score is the site used in clinical decisions.  It is used in pre menopausal women.

How do you use Z scores?

Z-score is less commonly used but may be helpful in identifying persons who should undergo a work-up for secondary causes of osteoporosis. Z-score is is useful in post menopausal women.

How to interpret improvement of BMD?

Always look at the sequential data. If there is improvement it could be either due to therapy or due to onset of osteoarthritis.

Date created: 12/17/2013