INTRODUCTION TO IMAGING PHYSICS CAPABILITIES AND LIMITATIONS. DAVID B. CHALPIN, MD. ASSISTANT PROFESSOR OF CLINICAL RADIOLOGY LSU HEALTH SCIENCES CENTER NEW ORLEANS, LA. GOALS. TO BECOME FAMILIAR WITH THE BASICS OF IMAGE GENERATION USING X-rays, CT, AND MRI
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ASSISTANT PROFESSOR OF
LSU HEALTH SCIENCES CENTER
NEW ORLEANS, LA
(denoted by a RED asterisk - *)
Electric current is passed through a filament, leading to e-emission, then striking target (W or Mb), leading to X-ray emission.
ASK YOUR PATIENTS TO
mAs compared with XR studies done w/o grids
Direction of emitted beam from the X-ray tube PatientCassette
DON’T MAKE GOOD CALLS FROM “BAD” FILMS !!
can mean Suboptimal QualityOR the study as ordered was NOT dedicated for evaluation of Region or Organ of Interest.
YOU CANNOT CALL WHAT YOU DON’T SEE!*
HOWEVER, IF YOU
GET ANOTHER VIEW!!*
IMAGES CAN BE MANIPULATED POST-ACQUISITION TO OPTIMIZE VIEWING OF ONE PART OF H&D Curve.
For monochromatic Photon energy –
log %T α 1/linear attenuation
The %Transmission of Photon energy received by detectors is recorded at multiple projections around the subject& the data is then reconstructed to create a cross-sectional image
*%Transmission of photon energyreceived by detectors is recorded at multiple projections around the subject
& the data is reconstructed to create
a cross-sectional image
µ - the intrinsic X-ray coefficient
a function of:
Hounsfield Units (H.U.)*
of sample S =
(μS - μH2O) x 1000
COMPARED WITH X-rays, U/S, & MRI
e.g. a Bony Sequestrum & Involucrum
SLIP RING TECHNOLOGY TO CREATE HELICAL ACQ’N!
→ MDCT !
Arterial; Hepatic Arterial;
Portal Venous; Renal Capillary;
Renal Excretion, etc.
But need mAs to compensate
MULTIPHASIC Imaging for assessing Contrast Enhancement over time within Organ(s) or Lesion(s) → Pt.Increased Radiation Dose if using CT
the Lowerthe S/N !!*
Processing of emitted RF signal yields SpatialInformationas
well as various forms of
PATIENTS MUST -
ILLUSTRATIONS COURTESY OF:
MRI in Practice, 3rd ed. Westbrook…
Clinical MRI Atlas, 2nd ed. Runge…
Radiologic Physics, 4th ed. Christenson…
Fundamentals of Radiology, LF Squire