Medical Imaging
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Patrizio Capasso, MD, is Professor and Division Chief of Vascular & Interventional Radiology in the Departments of Diagnostic Radiology and Surgery at the University of Kentucky Chandler Medical Center Lexington, Kentucky, USA.
Andrew R. Wyant, MD, is Assistant Professor for Physician Assistant Studies at the University of Kentucky Chandler Medical Center Lexington, Kentucky, USA. Among many other courses that he teaches is a popular clinical skills seminar in in Radiographic Interpretation.
Content
Preface x
Acknowledgments xiii
Introduction: Dr. Doe's Headaches: An Imaging Case Study xiv
Computed tomography xiv
Picture archiving and communication system xv
T1, T2, and FLAIR MRI xvi
MR spectroscopy and a virtual biopsy xvii
Functional MRI xviii
Diffusion tensor MR imaging xviii
MR guided biopsy xx
Pathology xxi
Positron emission tomography? xxi
Treatment and follow-up xxii
1 Sketches of the Standard Imaging Modalities: Different Ways of Creating Visible Contrast Among Tissues 1
"Roentgen has surely gone crazy!" 2
Different imaging probes interact with different tissues in different ways and yield different kinds of medical information 4
Twentieth-century (analog) radiography and fluoroscopy: contrast from differential attenuation of X-rays by tissues 7
Twenty-first century (digital) images and digital planar imaging: computer-based images and solid-state image receptors 16
Computed tomography: three-dimensional mapping of X-ray attenuation by tissues 17
Nuclear medicine, including SPECT and PET: contrast from the differential uptake of a radiopharmaceutical by tissues 20
Diagnostic ultrasound: contrast from differences in tissue elasticity or density 26
Magnetic resonance imaging: mapping the spatial distribution of spin-relaxation times of hydrogen nuclei in tissue water and lipids 28
Appendix: selection of imaging modalities to assist in medical diagnosis 30
References 36
2 Image Quality and Dose: What Constitutes a "Good" Medical Image? 37
A brief history of magnetism 37
About those probes and their interactions with matter . . . 39
The image quality quartet: contrast, resolution, stochastic (random) noise, artifacts - and always dose 47
Quality assurance 57
Known medical benefits versus potential radiation risks 61
3 Creating Subject Contrast in the Primary X-ray Image: Projection Maps of the Body from Differential Attenuation of X-rays by Tissues 67
Creating a (nearly) uniform beam of penetrating X-rays 69
Interaction of X-ray and gamma-ray photons with tissues or an image receptor 75
What a body does to the beam: subject contrast in the pattern of X-rays emerging from the patient 83
What the beam does to a body: dose and risk 87
4 Twentieth-century (Analog) Radiography and Fluoroscopy: Capturing the X-ray Shadow with a Film Cassette or an Image Intensifier Tube plus Electronic Optical Camera Combination 91
Recording the X-ray pattern emerging from the patient with a screen-film image receptor 92
Prime determinants/measures of image quality: contrast, resolution, random noise, artifacts, . . . and, always, patient dose 98
Special requirements for mammography 114
Image intensifier-tube fluoroscopy: viewing in real time 122
Conclusion: bringing radiography and fluoroscopy into the twenty-first century with solid-state digital X-ray image receptors 125
Reference 126
5 Radiation Dose and Radiogenic Risk: Ionization-Induced Damage to DNA can cause Stochastic, Deterministic, and Teratogenic Health Effects - And How To Protect Against Them 127
Our exposure to ionizing radiation has doubled over the past few decades 127
Radiation health effects are caused by damage to DNA 129
Stochastic health effects: cancer may arise from mutations in a single cell 132
Deterministic health effects at high doses: radiation killing of a large number of tissue cells 139
The Four Quartets of radiation safety 146
References 151
6 Twenty-first Century (Digital) Imaging: Computer-Based Representation, Acquisition, Processing, Storage, Transmission, and Analysis of Images 152
Digital computers 153
Digital acquisition and representation of an image 157
Digital image processing: enhancing tissue contrast, SNR, edge sharpness, etc. 166
Computer networks: PACS, RIS, and the Internet 168
Image analysis and interpretation: computer-assisted detection 170
Computer and computer-network security 172
Liquid crystal displays and other digital displays 173
The joy of digital 174
7 Digital Planar Imaging: Replacing Film and Image Intensifiers with Solid State, Electronic Image Receptors 176
Digital planar imaging modalities 176
Indirect detection with a fluorescent screen and a CCD 178
Computed radiography 178
Digital radiography with an active matrix flat panel imager 179
Digital mammography 184
Digital fluoroscopy and digital subtraction angiography 186
Digital tomosynthesis: planar imaging in three dimensions 189
References 190
8 Computed Tomography: Superior Contrast in Three-Dimensional X-Ray Attenuation Maps 191
Computed tomography maps out X-ray attenuation in two and three dimensions 192
Image reconstruction 198
Seven generations of CT scanners 204
Technology and image quality 208
Patient- and machine-caused artifacts 219
Dose and QA 221
Appendix: mathematical basis of filtered back-projection 229
References 233
9 Nuclear Medicine: Contrast from Differential Uptake of a Radiopharmaceutical by Tissues 234
Unstable atomic nuclei: radioactivity 235
Radiopharmaceuticals: gamma- or positron-emitting radionuclei attached to organ-specific agents 245
Imaging radiopharmaceutical concentration with a gamma camera 248
Static and dynamic studies 254
Tomographic nuclear imaging: SPECT and PET 260
Quality assurance and radiation safety 270
References 273
10 Diagnostic Ultrasound: Contrast from Differences in Tissue Elasticity or Density Across Boundaries 274
Medical ultrasound 274
The US beam: MHz compressional waves in tissues 277
Production of an ultrasound beam and detection of echoes with a transducer 280
Piezoelectric transducer elements 281
Transmission and attenuation of the beam within a homogeneous material 285
Reflection of the beam at an interface between materials with different acoustic impedances 288
Imaging in 1 and 1 × 1 dimensions: A- and M-modes 291
Imaging in two, three, and four dimensions: B-mode 294
Doppler imaging of blood flow 300
Elastography 302
Safety and QA 303
11 MRI in One Dimension and with No Relaxation: A Gentle Introduction to a Challenging Subject 307
Prologue to MRI 308
"Quantum" approach to proton nuclear magnetic resonance 310
Magnetic resonance imaging in one dimension 316
"Classical" approach to NMR 321
Free induction decay imaging (but without the decay) 331
Spin-echo imaging (still without T1 or T2 relaxation) 338
MRI instrumentation 343
Reference 351
12 Mapping T1 and T2 Relaxation in Three Dimensions 352
Longitudinal spin relaxation and T1 353
Transverse spin relaxation and T2-w images 364
T2* and the gradient-echo (G-E) pulse sequence 372
Into two and three dimensions 374
MR imaging of fluid movement/motion 382
13 Evolving and Experimental Modalities 387
Optical and near-infrared imaging 388
Molecular imaging and nanotechnology 390
Thermography 392
Terahertz (T-ray) imaging of epithelial tissues 393
Microwave and electron spin resonance imaging 393
Electroencephalography, magnetocardiography, and impedance imaging 394
Photo-acoustic imaging 396
Computer technology: the constant revolution 397
Imaging with a crystal ball 399
References 399
Suggested Further Reading 400
Index 403
