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MEDICAL SCANS. How they work, what they measure, and how to read them Hosted by MEDSOC – January 17, 2007. Computerized Tomography. Overview. Simply a series of 2-D X-Rays taken to create a 3-D picture Because of many X-Rays, dangerous exposure to radiation

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medical scans


How they work, what they measure, and how to read them

Hosted by MEDSOC – January 17, 2007

  • Simply a series of 2-D X-Rays taken to create a 3-D picture
  • Because of many X-Rays, dangerous exposure to radiation
  • CT scan measures differences in density of the tissues
  • 3-D nature extremely effective
how to read a ct scan
How to Read a CT Scan
  • Lighter areas have a higher density
when are ct scans used
When are CT Scans Used?
  • CT Scans are most commonly used with the skeletal system
  • Broad-spectrum analysis of anatomical changes/insults
  • 3-D nature allows analysis of breaks or other trauma from more than one perspective
the chem 7 test
The CHEM-7 Test
  • Analysis of 7 different chemicals in the blood
  • Determines chemical level and concentration
  • Indicates abnormalities in tissues
blood urea nitrogen bun
Blood Urea Nitrogen (BUN)
  • Urea Nitrogen: present when amino acids break down and NH4+ (ammonium) combines with other substances
  • Usually indicates kidney and liver function
  • Normal levels: 7 to 20 mg/dl
  • Too low: liver failure, malnutrition, over-hydration
  • Too high: starvation, low protein, kidney disease/failure, heart attack, urinary track obstruction
serum chloride
Serum Chloride
  • Chloride maintains electric neutrality by counter-ion to sodium
  • Normal Range: 101 to 111 mmol/L
  • Too low: blood is acidic (acidosis), low bicarbonate levels, malfunctioning kidney
  • Too high: hormone deficiency (Addison’s disease, respiratory acidosis)
carbon dioxide
Carbon Dioxide
  • Measures CO2 and HCO3 (bicarbonate)
  • Kidney and Respiratory function
  • Normal: 20 to 29 mmol/L
  • Too low: problem with kidney
  • Too high: liver dysfunction
  • Breakdown product of creatine, an important part of muscle
  • Evaluates kidney function
  • Normal value: 0.8 to 1.4 mg/dl
  • Too low: muscular dystrophy
  • Too high: kidney disease/failure
  • Blood sugar levels
  • Can be used to diagnose diabetes
  • Normal level: 100 mg/dL
  • Too high: most likely at risk of diabetes (greater than 100 mg/dL), diabetes diagnosed if greater than 100 mg/dL
  • Too low: too much insulin (rare)
  • Positive ion in maintaining electric charge
  • Normal range: 3.7 to 5.2 mEq/L
  • Too high: kidney failure, respiratory acidosis
  • Too low: improper diet, narrowing of major blood vessels to kidney
  • Sodium content in blood
  • Normal level: 135 to 145 mEq/L
  • Too high: Excessive sweating, too much aldosterone or cortisol
  • Too low: dehydration, heart failure, kidney disease, cirrhosis of liver, improper hormone levels (too high or low)
blood pressure
Blood Pressure
  • Stethoscope and sphygmomanometer
  • Measures pressure blood exerts on arteries
  • Highest pressure: systolic
  • Lowest pressure: diastolic
  • Typical adult blood pressure: 120 mmHg (systolic) and 80 mmHg (diastolic)
  • High blood pressure may lead to heart attacks, stroke
  • Low blood pressure needs urgent medical attention
  • Basic Design: a giant cube
  • Horizontal Tube Magnet- bore
  • Body part to be examined must be at the isocenter
  • Used for diagnosing various medical problems because of its flexibility in producing data.
the physics
The Physics
  • Rating unit: tesla or gauss
  • 3 Types of magnets in the MRI system:
    • Resistive Magnets
    • Permanent Magnets
    • Superconducting Magnets
the physics21
The Physics
  • Resistive Magnets
    • Windings/coils of wire wrapped around a bore through which a current is passed
    • Require huge amounts of electricity
the physics22
The Physics
  • Permanent Magnets
    • Magnet that suits its name- magnetic field is always present
    • Extremely heavy (drawback)
the physics23
The Physics
  • Superconducting Magnets
    • Most commonly used in MRIs
    • Similar to the resistive magnet but… wire is continually bathed in liquid helium at -425.4oC.
    • Electricity required is substantially less
the physics24
The Physics
  • Magnetic Fields
    • Homogenous- stable magnetic field; good for high quality imaging
    • Gradient Magnet- Three of these in every MRI machine; low strength
    • Main Magnet(resistive, etc.) -stable magnetic field
    • Gradient magnets- variable magnetic field
the physics25
The Physics
  • Machine adds radio frequency pulse to area tested
  • Pulse causes protons in the area to spin
  • Pulse is transmitted through a coil that is specific to the body part tested
  • Gradient magnets alter magnetic field at local level
the physics26
The Physics
  • As protons return to natural alignment, the coil picks the signals from the protons, and then sends the info to a computer system which then converts it the info into a picture using the fourier system.
how to read an mri
How to Read an MRI
  • Black areas- where there is lesser hydrogen atoms in the tissue
  • White/Brighter areas- where there are many protons in the tissue- e.g.: fatty tissue
  • Tumors and “Diseases” are detected when they differ from the standard and when usually a conspicuous white “blob” is observed
when are mri scans used
When are MRI Scans Used?
  • Hydrogen atoms v. Hydrogen ions
  • May be used to differentiate between water and fatty tissue
  • Anatomical abnormalities
  • PET Scans involve radioactive isotopes
  • Radioactive isotopes are injected into bloodstream
  • Machine measures radioactivity
  • Constructs 2-D or 3-D image of body
the physics32
The Physics
  • Radioactive isotopes are chemically incorporated into metabolically active molecule
  • Host cells uptake radioactivity based on metabolic rate
  • Water, glucose
  • Radioactivity generates a positron
  • Annihilates with electron
the physics33
The Physics
  • Annihilation produces a pair of gamma photons
  • Measured by machine
  • Delay measured to remove data from random photons
  • Millions of these data points are collected and analyzed
how to read a pet scan
How to Read a PET Scan
  • Areas of high intensity (red) indicate high metabolic rate
  • This may correlate to high water uptake or glucose uptake, depending on which radioactive material you use
  • Usually used in conjunction with CT or MRI
when are pet scans used
When are PET Scans Used?
  • PET scans may be sensitive to changes in chemical compositions or metabolic rates even before physiological marker is present
  • CT, MRI for anatomical signal
  • Cancers almost always have different metabolic rates