Anatomy in Diagnostic Imaging (eBook)

Peter Fleckenstein, Jørgen Tranum-Jensen (Autoren)

eBook Download: EPUB

2014 | 3. Auflage
John Wiley & Sons (Verlag)
978-1-118-49955-9 (ISBN)

Infos

Now in its third edition, Anatomy in Diagnostic Imaging is an unrivalled atlas of anatomy applied to diagnostic imaging. The book covers the entire human body and employs all the imaging modalities used in clinical practice; x-ray, CT, MR, PET, ultrasound and scintigraphy. An introductory chapter explains succinctly the essentials of the imaging and examination techniques drawing on the latest technical developments.

In view of the great strides that have been made in this area recently, all chapters have been thoroughly revised in this third edition. The book's original and didactically convincing presentation has been enhanced with over 250 new images. There are now more than 900 images, all carefully selected in order to be user-friendly and easy-to-read, due to their high quality and the comprehensive anatomical interpretation directly placed alongside every one.

Both for medical students and practising doctors, Anatomy in Diagnostic Imaging will serve as the go-to all-round reference collection linking anatomy and modern diagnostic imaging.
Winner of the Radiology category at the BMA Book Awards 2015

Peter Fleckenstein MD, Emeritus Chief Radiologist and Lecturer of Radiological Anatomy, University of Copenhagen, Denmark

Jørgen Tranum-Jensen MD, Professor of Anatomy, Panuminstituttet, University of Copenhagen, Denmark

Co-author:
Peter Sand Myschetzky MD, Chief Physician, Radiology, University of Copenhagen, Denmark

Inhalt

Principles and Techniques in Diagnostic Imaging

Techniques based on X-rays

Techniques based on nuclear magnetic resonance

Techniques based on ultrasound reflection

Techniques based on radioisotope emissions

Principles of nomenclature and positioning

Upper Limb

Shoulder and arm

Elbow

Forearm

Wrist and hand

Arteries and veins

Lower Limb

Pelvis

Hip and thigh

Knee

Leg

Ankle and foot

Arteries and veins

Lymphatics

Spine

Cervical spine

Thoracic spine

Lumbar spine

Head

Skull

Ear

Orbit

Paranasal sinuses

Temporomandibular joint

Teeth

Salivary glands

Arteries

Brain

Arteries and veins

Newborn

Neck

Larynx

Pharynx

Axial CT series

Thyroid gland

Thorax

Thoracic cage

Axial CT series

Heart and great vessels

Esophagus

Breast

Thoracic duct

Abdomen

Axial CT series

Stomach

Small intestine

Colon and rectum

Liver and pancreas

Spleen

Arteries and veins

Lymphatics

Urogenital system

Kidney

Urinary bladder and urethra

Male genital organs

Female genital organs/embryo

Fetus

Short Dictionary of Examination Procedures and Concepts in Diagnostic Imaging

Index

Rezensionen

"There are now more than 900 images, all carefully
selected in order to be user-friendly and
easy-to-read, due to their high quality and the
comprehensive anatomical interpretation directly placed alongside
every one. Both for medical students and practising doctors,
Anatomy in Diagnostic Imaging , Third edition will serve as the
go-to all-round reference collection linking anatomy
and modern diagnostic imaging." (Kingbook73's
Medical Ebook and Video Collection, 28 November 2014)

Textauszug

Techniques Based on X-Rays

The Generation and Nature of X-Rays

X-rays occupy a range within the electromagnetic wave spectrum. For purposes of diagnostic imaging, useful wavelengths are between 0.06 and 0.006 nm. Unlike visible light, X-rays cannot be deflected by lenses or analogous devices. Diffraction and wave optics can therefore largely be ignored in diagnostic imaging with X-rays. It is useful to picture X-rays as linearly propagating streams of indivisible quanta of energy, photons. Accordingly, X-rays are commonly characterized by their photon energies rather than by their wavelengths or their wave frequency. Because X-rays are generated by conversion of the energy acquired by electrons accelerated through an electric field in the kilo-volt (kV) range, the convenient unit for X-ray photon energies is the kilo-electron-volt (keV); the diagnostic relevant range being 20–200 keV (Figure 1).

The propagation velocity (c) of electromagnetic waves is constant (in vacuo): 3 × 1017 nm × sec−1, and relates to wavelength (λ) and frequency (ν) by: c = λ × ν.

Electromagnetic waves are emitted as discrete quanta of energy (photons). The energy (E) of a photon relates to its frequency (ν) by: , where h is Planck's constant. If energy is expressed in keV and wavelength (λ) in nanometers, the relation becomes: .

One electron volt (eV) is the energy acquired by an electron accelerated through a gradient of one volt. 1000 eV = 1 keV.

Figure 1  The electromagnetic wave spectrum, given by wavelength, frequency and photon energy.

The X-Ray Tube

The source of X-rays for diagnostic imaging is the X-ray tube (Figure 2) in which a narrow beam of electrons, emitted from an electrically heated tungsten filament (the cathode), is accelerated in vacuo and focused electrostatically to impinge the target anode that emits a small fraction (0.2–2%) of the incident electron energy as X-rays. The rest of the energy dissipates as heat in the anode, which usually is made from a tungsten alloy with high thermal stability, shaped as a disc and rotating at high speed to spread the thermal load evenly over a large area.

Figure 2  Diagrammatic presentation of the basic elements of a diagnostic X-ray tube.
Details of circuitry are not given.

1. 1: Cathode filament
2. 2: Electron beam
3. 3: Rotating anode
4. 4: Anode motor drive
5. 5: Vacuum tube
6. 6: Lead shield
7. 7: Window
8. 8: Central ray

The energy (wavelength) of the X-rays generated by the tube is primarily controlled by adjustment of the electrical potential difference between the cathode and the anode, the accelerating voltage. The high voltage is generated by rectification and high voltage transformation of common 50–60 Hz alternating current (AC) which has been converted up to some 50,000 Hz AC. Evening-out is incomplete and the high voltage is rippled. The ripple is expressed as the difference between the peak and the minimum voltage in per cent of the peak voltage and mounts to 5–10% in most high voltage generators. The high voltage setting of an X-ray unit usually refers to the peak voltage and is denoted kVp to indicate this fact.

The intensity of X-rays produced by the tube at a given voltage setting is determined by the number of electrons hitting the anode, that is, the current carried by the electrons through the vacuum from the cathode to the anode, termed the beam (or tube) current and expressed in milliamperes (mA). For accelerating voltages above some 40 kV (the saturation voltage), the beam current is largely determined by the cathode filament temperature only and can be regulated by the filament heating current supply.

The quantity (dose) of X-rays delivered by the tube is proportional to the time the beam current flows and is conveniently expressed as milliampere seconds (mAs).

The X-ray photons emitted by the anode distribute with varying intensity over a spectrum with a maximum set by the peak accelerating voltage of the tube. Thus, the X-ray beam is polychromatic. Even if the accelerating voltage is constant (not rippled) the beam is still highly polychro­­matic due to the nature of the process by which X-rays are generated at the anode (“bremsstrahlung”), not to be elaborated here.

Photons with energies below some 20 keV are useless for most radiography purposes because they cannot penetrate the body parts examined. Still they are harmful because their energy is absorbed superficially in the irradiated tissue, especially the skin. Insertion of thin aluminum or copper plates, filters, in the path of the X-ray beam removes these unwanted low energy photons (Figure 3). The mean photon energy thereby increases; the beam is said to be hardened. Mammography employs the lowest photon energies in diagnostic X-ray imaging, around 25–30 keV, in order to optimize detection of the very small differences in X-ray absorption between normal and cancerous tissue.

Figure 3  The effect of filtering on the distribution of photon energies in the X-ray beam from a 100 kVp tube.
Even the unfiltered beam has been “filtered” by passage through the wall of the X-ray tube whereby the lowest energies have been rejected. Additional filtering lowers the overall intensity, but increases the mean photon energy.

The X-ray tube is surrounded by a lead shield with a window that permits passage of the X-rays. The size and shape of the window, the aperture, can be varied by means of adjustable diaphragms (Figure 2). The X-rays radiate from the tube as a diverging bundle originating from the area on the anode hit by the electron beam, the “focus”, and limited by the tube exit aperture. The axis of the bundle is called the central ray, and the focus viewed along this axis is called the effective focal spot. The smaller this spot, the better the resolution in the radiograph. They are mostly in the order of 1 mm2 or less; in mammography down to 0.1 mm2 which allows detection of the tiny calcium deposits often found in malignant mammary tumors.

The X-ray beam should always be restricted by the diaphragms to illuminate the minimally required area of the body to minimize radiation exposure. This adjustment is called collimation.

Interactions of X-Rays with Matter

At the X-ray energies applied in diagnostic imaging, three types of interaction are to be considered: elastic scatter, the photoelectric effect, and inelastic (Compton) scatter.

Elastic scatter is an interaction whereby photons undergo a change of direction without loss of energy. This type of scatter takes place at all diagnostically relevant photon energies, but accounts for only a few per cent of the total scatter.

The photoelectric effect (Figure 4) is an interaction in which the incident X-ray photon delivers all of its energy to an atom which in turn releases this energy in the form of an electron, a photoelectron, which is ejected from one of the inner electron shells of the atom at high speed. An electron from one of the outer shells soon “falls in” to fill the vacancy, and energy is concomitantly released in the form of a new X-ray photon, emitted in a random direction and with an energy that is characteristic for the particular element. This secondary photon is of lower energy than the exiting photon. It may emerge as secondary radiation from the object, but is mostly absorbed by new interactions. The atom is left ionized, and the released electron collides with other atoms and causes a large number of secondary ionizations. The photoelectric effect is strong when the incident photon energy is just moderately higher than the binding energy of an inner shell electron. Only the two electrons in the innermost shell, the K-shell, have binding energies sufficiently high to engage in photoelectric interactions within the diagnostically relevant X-ray energy range. The photon energy, just sufficient to release a photoelectron from the K-shell, is denoted a K-edge, because the X-ray attenuation increases steeply as a threshold phenomenon at this energy level (Figure 5). The K-edges have characteristic values for different elements (Table 1). In soft tissues composed of lighter elements (C, N, O), photoelectric attenuation becomes quantitatively unimportant at photon energies above some 35 keV. Because the binding energy of K-shell electrons is higher for higher elements (such as calcium), the photoelectric effect remains quantitatively important for bone imaging up to some 50 keV. Barium and iodine have their K-edges at 37 keV and 33 keV, respectively. It is these high K-edges that are utilized when barium and iodine are used in contrast media.

Figure 4  The photoelectric interaction. Figure 5  The K-edge effect.
X-ray absorption increases steeply at photon energies equal to the binding energy of the K-shell electrons of an element, a so-called K-edge.

Table 1

  

Element	K-edge...

Produkt-Details

• Erscheint lt. Verlag: 25.7.2014
• Sprache: englisch
• Themenwelt: Medizinische Fachgebiete ► Radiologie / Bildgebende Verfahren ► Radiologie
• Themenwelt: Studium ► 1. Studienabschnitt (Vorklinik) ► Anatomie / Neuroanatomie
• Themenwelt: Studium ► 2. Studienabschnitt (Klinik) ► Anamnese / Körperliche Untersuchung
• Schlagworte: Anatomie • Anatomie u. Physiologie • anatomy • Anatomy & Physiology • area • Atlas • Biowissenschaften • Body • Book • Chapters • Clinical • Developments • Diagnostic • Edition • entire • Essentials • Examination • explains • Great • introductory • Latest • Life Sciences • Medical Science • Medizin • Modalities • Practice • Radiologie • Radiologie u. Bildgebende Verfahren • Radiology & Imaging • recently • strides • technical • techniques • Third • unrivalled • View
• ISBN-10: 1-118-49955-7 / 1118499557
• ISBN-13: 978-1-118-49955-9 / 9781118499559