The Principles of Diagnostic Imaging

Loading...

The Principles of Diagnostic Imaging Stephen J Mather Barts and the London School of Medicine and Dentistry, Queen Mary University of London. [email protected] Khuloud T Al-Jamal Institute of Pharmaceutical Sciences University College London [email protected] Imaging Principles

Objectives for this lecture • To teach the basic principles of diagnostic imaging with – – – –

X-rays (planar and CT) Magnetic Resonance Ultrasound Radionuclide (SPECT and PET)

Imaging Principles

Imaging employs electromagnetic radiation

Imaging Principles

Medical Imaging modalities X-ray CT – (X-ray computed tomography) uses ionising radiation, source is external to the body. In some cases, contrast agents are injected. Anatomical images MRI (Magnetic resonance imaging) – uses magnetic fields and radiofrequency pulses to produce anatomical images. In some cases, contrast agents are injected. Also, fMRI US (Ultrasound imaging) – uses high frequency sound waves and the pulse echo effect (which is the basis of radar) to give anatomical information. Nuclear medicine imaging – uses unsealed radioactivity to produce functional images

Imaging Principles

The beginnings of Radiology November 1895 - Roentgen discovered X-rays



when experimenting with cathode ray tubes in a darkened room, he noticed a faint fluorescent glow emanating from a plate he had left on the bench



when he moved to pick it up, he was amazed to see the image of the bones from his hand cast onto the plates



the prospects for x-ray diagnosis were immediately recognised but Roentgen refused to patent his discovery



Won first Nobel Prize in Physics for his discovery - 1901

Imaging Principles

Planar - X-ray Modern direct capture Radiography

Early X-ray apparatus ~ 1920’s

Imaging Principles

X-ray tube

Imaging Principles

Production of characteristic X-rays

Imaging Principles

Production of Bremsstrahlung X-rays

Imaging Principles

Process of Image Production • X-rays produced • X-ray photons are either: Attenuated, Absorbed, Scattered, Transmitted • air < fat < fluid < soft tissue < bone < metal • Transmitted X-ray photons (+some scatter) reaches the cassette and may interact with: Intensifying screens (produce light) or Film • Latent image (i.e. undeveloped) produced which is then processed. Imaging Principles

Producing a Radiograph

Imaging Principles

Digital images

Imaging Principles

Direct Capture Radiography • Direct capture Imaging System • No Cassettes • Amorphous Silicate used as detector material • Similar to digital simulator/ treatment setup

Imaging Principles

Factors affecting Radiograph • • • •

Scatter Distance Movement kVp and mAs settings

Imaging Principles

The normal CXR • First of all is the film technically adequate ?  Correct area imaged   Inspiratory effort   Penetration  Rotation  Annotation 

FUNGAL PNEUMONIA

TUMOUR

Aggressive- fibrosarcoma

Non- aggressive- aneurysmal bone cyst

Aggressive- Ewings tumour

Fluoroscopy

Imaging Principles

Computerised X-ray Tomography

Imaging Principles

Computerised X-ray Tomography

Imaging Principles

CT numbers Linear attenuation coefficient µ = Fraction of energy absorbed

Tissue

approx CT number

dense bone Muscle white matter grey matter Blood CSF Water Fat Lungs Air

1000 50 45 40 20 15 0 -100 - 200 - 1000

Imaging Principles

Radiation doses • • • •

CT head CT chest CT abdomen CT pelvis

2.5 mSv 8 mSv 10 mSv 10 mSv

• chest radiograph PA • abdomen radiograph AP • pelvis radiograph AP

Imaging Principles

0.02 mSv 0.7 mSv 0.7 mSv

X-ray Contrast Agents •

substances with high atomic numbers have high density which is useful for X-ray contrast. Appear bright white in X-ray exams



e.g. Barium (atomic number 56) causes considerable attenuation of X-rays compared with the soft tissues of the body (used for barium meals and barium enema’s for diagnosis in the gastrointestinal tract) (Barium sulfate - inert) used mainly for plain radiographs



Salts of iodine (atomic no. 53) are used as water soluble CT contrast agents. Can be injected intravascularly or into any cavity, sinus or tract. Can also give an indication of function e.g. filtration by the kidney. Can be toxic- allergic side effects.

Imaging Principles

Applications of Imaging in Cancer

• • • •

Diagnosis Staging Monitoring response Detection of recurrence

Imaging Principles

Diagnosis

Imaging Principles

Staging – local spread

Staging – local spread

Imaging Principles

Staging – lymph nodes

Imaging Principles

Staging – distant spread

Imaging Principles

Magnetic Resonance Imaging • The newest imaging modality • Principle used in spectroscopy since 1950s • First human scan 1977 • Adopted for clinical use ~ 1988 • Approximately 300 in the UK (compared with approximately 500 CT scanners which have been around since 1971!) Imaging Principles

Magnetic Resonance Imaging • MRI gives superior soft tissue discrimination compared with CT: large differences in signals emitted from different soft tissues

Imaging Principles

Principle of MRI

The spinning single proton in a hydrogen atom creates a magnetic field and each hydrogen atom acts like a tiny magnet

Imaging Principles

Principle of MRI In the absence of an external magnetic field Hydrogen nuclei magnetic moments are randomly oriented and have a net magnetization of zero. In the presence of an external magnetic field hydrogen protons align themselves in one of two directions, parallel or anti-parallel to the net magnetic field producing a net magnetic field (Mo) Imaging Principles

Precession

The hydrogen atoms are not still but ‘wobble’ or ‘precess’ like a spinning top in the direction of the external magnetic field Larmor (or precessional) frequency (wO) = B0 x l Where B0 is the magnetic field and l is the ‘gyromagnetic ratio’

Imaging Principles

Resonance If an RF pulse at the Larmor frequency is applied to the nucleus of an atom, the protons will absorb some energy and alter their alignment away from the direction of the main magnetic field .

As well as changing direction the protons also begin to precess ‘in phase’ resulting in a net magnetic moment transverse to the external field which induces a current and is detected in the transiever coil Imaging Principles

Principles of MRI When the RF is switched off, the protons: 1. Give up the energy they have absorbed and start to return to their previous direction 2. Start to precess out of frequency With the result that • Longitudinal magnetization gradually increases called T1 recovery • Transverse magnetization gradually decreases called T2 decay

Imaging Principles

T1 and T2 The rate at which these processes occur vary from tissue to tissue

Imaging Principles

Imaging Parameters The duration, repetition, timing and amplitude of RF pulse sequences are varied to produce signals which can be analysed in different ways in order to ‘weight’ the image.

T1 weighted

Proton density weighted Imaging Principles

T2 weighted

Signal intensities on T1

High: Fat, bone marrow, contrast agents Intermediate: Soft Tissues Low: Water (urine, CSF)

Imaging Principles

Signal intensities on T2

High: Fat, Water Intermediate: Soft tissue Low: Tendons

Imaging Principles

MR contrast agents The most common contrast agents are Gadolinium chelates (DOTA, DTPA, DO3A etc) which interact with the water molecules in its vicinity to produce white areas in T1 weighted images

T2

T1 +Gd

Imaging Principles

Ovarian Cancer within endometrial cyst

Pre -Gd

Post Gd

Imaging Principles

Iron-oxide particles-darken on T2

Malignant Benign Imaging Principles

Mn-DPDP – brightens liver on T1

T1 + ‘Teslascan’

T1

Manganese(II)-dipyridoxal diphosphate (Mn-DPDP) Imaging Principles

Magnetic resonance spectroscopy • allows examination of individual molecules within a sample • MRS can be used to study the biochemical nature of disease • looks at concentrations of different substances in tissue to identify disease • e.g. brain spectra can give concentrations of N-acetyl aspartate (NAA), creatine/phosphocreatine and choline. In patients with temporal lobe epilepsy, the levels of NAA are reduced and the levels of creatine/phosphocreatine and choline are increased in the diseased lobe • e.g. lipid concentration can be used to grade tumours Imaging Principles

Ultrasound imaging • Ultrasound imaging is based on the pulseecho principle, which is also the basis of radar • It only came into use as a medical imaging technique after WW2 during which fast electronic pulse technology was developed • first 2-D ultrasound scan in a living subject (of a myoblastoma in the leg) was carried out in 1951 • 1961 - first scan of pregnant abdomen

Imaging Principles

Diagnostic ultrasound • Ultrasound imaging uses ultra-high-frequency sound waves (3-10 MHz). Human hearing - 20 to 20 000 Hz • a Piezoelectric transducer ( a "crystalline" material such as quartz that changes shape when an electric current is applied creating sound waves and when struck by sound waves creates electrical currents) • ultrasonic waves are emitted by the transducer and travel through human tissues at a velocity of 1540 m s-1. When the wave reaches an object or surface with a different texture or acoustic nature, a wave is reflected back • these echoes are received by the apparatus, changed into electric current and a 2-D image is produced • more than 20 frames can be generated per second, giving a smooth, realtime image Imaging Principles

Diagnostic Ultrasound • The stronger the returning signal, the more white it will be on the grey-scale image (hyperechoic = white or light grey e.g. fat containing tissues) • hypoechoic = dark grey (e.g. lymphoma, fibroadenoma of the breast) • pure fluid gives no echoes, appearing black (anechoic) leading to acoustic enhancement of tissues distal to e.g. gallbladder and urinary bladder • acoustic shadow is the opposite effect where tissues distal to e.g. gas containing areas, gallstones, renal stones receive little sound and thus appear as black Imaging Principles

Imaging Principles

Ultrasound - disadvantages • interactive modality, operator dependent • ultrasound waves are greatly reflected by air-soft tissue and bone-soft tissue interfaces, thus limiting its use in the head, chest and musculoskeletal system

Ultrasound image of gallstone (G) causing accoustic shadow (S). L = liver Imaging Principles

Doppler Ultrasound • Doppler effect: the influence of a moving object on sound waves • object travelling towards listener causes compression of sound waves (higher frequency) • object travelling away from listener gives lower frequency • flowing blood causes an alteration to the frequency of the sound waves returning to the ultrasound probe, allowing quantitation of blood flow •

Colour Doppler shows blood flowing towards the transducer as red, blood flowing away as blue - particularly useful in echocardiography and identifying very small blood vessels Imaging Principles

Nuclear Medicine GG.the clinical application of ‘unsealed’ radioisotopes or ‘radiopharmaceuticals’

Imaging Principles

The discovery of Radioactivity

• In 1896, Henri Becquerel discovered that uranium (and its salts) emitted radiation • 2 years later, Pierre and Marie Curie showed that uranium rays were an atomic phenomenon characteristic of the element, and not related to its chemical or physical state. • They called this phenomenon “radioactivity” • Becquerel and the Curies shared the Nobel Prize for Physics - 1903

Imaging Principles



In 1931, Ernest Lawrence invented the cyclotron and it became possible to produce artificial radioisotopes



99mTc



the first nuclear medicine scan (131Ithyroid) was carried out in 1948 (point by point)

was first produced by a 37 inch cyclotron in 1938

Ernest Lawrence Imaging Principles

•planar imaging using an Anger camera - 1957 •1967 SPET with Anger camera (rotating the patient on a chair in front of the camera) •1978 - first commercial gammacamera-based SPECT systems •The beginnings of PET (the technique of counting gammas from positron annhilation) had come about in 1951 and images were produced in 1953 Imaging Principles

Hal Anger with his invention, the scintillation camera

Nuclear Medicine Imaging

• Three types of emissions from radioactive isotopes: α particles, β particles and γ-rays (also some associated X-rays) • only γ-rays are useful for radioisotope imaging (high energy photons) • In radioisotope imaging, source is inside the body (X-ray CT – source is external).

Imaging Principles

Nuclear Medicine • Radiolabelled tracer (Radiopharmaceutical) is administered • γ-rays (high energy photons) emitted by the radioisotope are detected outside the body on a ‘Gamma camera’ • Lead ‘collimators’ are used to absorb scattered γ-rays • γ-rays impinge on sodium iodide crystals (dense enough to stop the photons) and converted into light which is detected by photomultipliers.

Imaging Principles

Photomultiplier tubes NaI crystal Lead collimator

Object

Photon Detection • photon is converted by scintillation crystal to flash of light • Crystal is coupled to Photomultiplier Tube • Photocathode converts light to electron. • Electron avalanche leads to electronic pulse

Imaging Principles

HV

PM tube

Crystal

Gamma-camera Principle Patient Gamma radiation Crystal

Collimator Photomultiplier Acquisition module Image processor Imaging Principles

Functional Imaging

Normal distribution of bone function Imaging Principles

Abnormal distribution

Quantitative Dynamic acquisition

Imaging Principles

Renogram with absent Left kidney function Imaging Principles

Dynamic MAG-3 kidney transplant study

Imaging Principles

Tomographic acquisition (SPECT)

Imaging Principles

Myocardial perfusion

Imaging Principles

3-D Rendering

SYSTOLE

DIASTOLE Imaging Principles

Beating mouse heart

Imaging Principles

Positron Emission Tomography (PET)

Imaging Principles

Imaging Principles

PET coincidence detection bismuth germanate (BGO) or Lutetium Oxyorthoscilicate (LSO) crystals • No collimators • High sensitivity • Picomolar concentrations • Absolute quantification (moles per microlitre)

Imaging Principles

Fluorodeoxyglucose -FDG

• Substrate for glucose transporters • undergoes phosphorylation • No further metabolism

Imaging Principles

FDG shows increased tumour uptake Head and Neck

Lung cancer

Imaging Principles

FDG-whole body PET showed increased glucose metabolism, highly suspicious for metastatic breast carcinoma. Fine-needle aspiration revealed metastatic adenocarcinoma. NOTE: MRI is negative Imaging Principles

Gd contrast MRI

FDG-PET

Image overlay

Glucose metabolism is very low on the first PET study

Imaging Principles

Gd contrast MRI

FDG-PET

Image overlay

FDG-PET uptake has increased three months later. This suggests tumor recurrence, and effectively rules out radiation necrosis.

Imaging Principles

Biologically relevant radionuclides From Kaschten et al., JNM, 39 (1998), 778

CH3 S

C-11 methionine

HO O

O HO

11

C

OH

OH

NH2 Imaging Principles

HO

18

F

FDG

Imaging Principles

Comparison of PET and SPECT Biological isotopes can be used for PET High sensitivity (arising from coincidence detection) and better image resolution Collimators essential for SPECT (much of signal is lost) Attenuation correction in PET is simple - in SPECT it is v.complex PET can be quantitative Fast - detector ring in PET collects much more of the signal and no need for gantry rotation However SPECT is much more commonplace and is cheaper than PET Access to a local cyclotron essential in PET Imaging Principles

Imaging Principles

PET-CT - The best of both worlds Combines functional information from PET with anatomical location provided by CT

Imaging Principles

PET-CT

Imaging Principles

PET/CT shows an area of increased uptake in the left nasopharynx and physiologic increased uptake inferior oral cavity and tongue.

Imaging Principles

Loading...

The Principles of Diagnostic Imaging

The Principles of Diagnostic Imaging Stephen J Mather Barts and the London School of Medicine and Dentistry, Queen Mary University of London. s.j.math...

3MB Sizes 6 Downloads 0 Views

Recommend Documents

Diagnostic Imaging - Buch.de
Diagnostic imaging. — 7th ed. / Andrea G. Rockall ... [et al.]. p. ; cm. Rev. ed. of: Diagnostic imaging / Peter Armst

Diagnostic Imaging Utilization Management - BCBSNC
Aug 16, 2010 - Refers to non-traumatic, non-CVA and non-tumor-related intra-cranial bleed. Examples include hypertensive

Meningitis (Suspected) - Diagnostic Imaging Pathways
Diagnostic Imaging Pathways - Meningitis (Suspected). Printed from ... SYMBOL. RRL. EFFECTIVE DOSE RANGE. None. 0. Minim

WHO Manual of Diagnostic Imaging (The). Radiographic Anatomy and
18 • THE WHO MANUAL OF DIAGNOSTIC IMAGING. 3.11 Arm. Figure 3.29. Arm, AP projection. Figure 3.30. Arm, lateral projec

WHO Manual of Diagnostic Imaging (The). Radiographic Anatomy and
Jan 10, 2010 - and omissions excepted, the names of proprietary products are distinguished by initial capital letters. .

Abdominal Pain (Chronic) - Diagnostic Imaging Pathways
File Formats. Some documents for download on this website are in a Portable Document Format (PDF). To read these files y

Paediatric, Hydronephrosis (Antenatal) - Diagnostic Imaging Pathways
This pathway provides guidance for imaging newborn and paediatric patients with antenatally detected hydronephrosis.

RATES FOR DIAGNOSTIC LABS & IMAGING CENTRES
RATES FOR DIAGNOSTIC LABS & IMAGING. CENTRES HYDERABAD. NAME OF INVESTIGATION. NABL /. Imaging. Non NABL. DENTAL. Dental

Paediatric, Pneumonia (Recurrent or Persistent) - Diagnostic Imaging
This pathway provides guidance on the imaging of paediatric patients with recurrent pneumonia. ... SYMBOL. RRL. EFFECTIV

Spinal Cord Compression (Suspected) - Diagnostic Imaging Pathways
points. Clicking on the PINK text box will bring up the full text. The relative radiation level (RRL) of each imaging in