NUCLEAR MEDICINE FOR MEDICAL STUDENTS AND JUNIOR DOCTORS Dr JOHN W FRANK M.Sc, FRCP, FRCR, FBIR PAST PRESIDENT, BRITISH NUCLEAR MEDICINE SOCIETY DEPARTMENT OF NUCLEAR MEDICINE, 1ST MEDICAL FACULTY, CHARLES UNIVERSITY, PRAGUE 2009 [1] ACKNOWLEDGEMENTS I would very much like to thank Prof Martin Šámal, Head of Department, for proposing this project, and the following colleagues for generously providing images and illustrations. Dr Sally Barrington, Dept of Nuclear Medicine, St Thomas’s Hospital, London Professor Otakar Bělohlávek, PET Centre, Na Homolce Hospital, Prague Dr Gary Cook, Dept of Nuclear Medicine, Royal Marsden Hospital, London Professor Greg Daniel, formerly at Dept of Veterinary Medicine, University of Tennessee, currently at Virginia Polytechnic Institute and State University (Virginia Tech), Past President, American College of Veterinary Radiology Dr Andrew Hilson, Dept of Nuclear Medicine, Royal Free Hospital, London, Past President, British Nuclear Medicine Society Dr Iva Kantorová, PET Centre, Na Homolce Hospital, Prague Dr Paul Kemp, Dept of Nuclear Medicine, Southampton University Hospital Dr Jozef Kubinyi, Institute of Nuclear Medicine, 1st Medical Faculty, Charles University Dr Tom Nunan, Dept of Nuclear Medicine, St Thomas’s Hospital, London Dr Kathelijne Peremans, Dept of Veterinary Medicine, University of Ghent Dr Teresa Szyszko, Dept of Nuclear Medicine, St Thomas’s Hospital, London Ms Wendy Wallis, Dept of Nuclear Medicine, Charing Cross Hospital, London Copyright notice The complete text and illustrations are copyright to the author, and this will be strictly enforced. Students, both undergraduate and postgraduate, may print one copy only for personal use. Any quotations from the text must be fully acknowledged. It is forbidden to incorporate any of the illustrations or diagrams into any other work, whether printed, electronic or for oral presentation. [2] CONTENTS Introduction p 5 History p11 Clinical studies p19 Bone, soft tissue and infection p19 Breast p32 Sentinel node p37 Lymphatics p38 Cardiac p40 Endocrine p47 Pituitary p47 Thyroid p48 Parathyroid p52 Pancreas p54 Adrenals p57 Ovaries/testes p64 Neuroendocrine p64 Gastro-intestinal p67 Gastric emptying p67 Oesophageal transit p68 Inflammatory disease p70 Bleeding p73 Meckel’s p74 Hepato-biliary p75 Head and neck p82 Vocal cord p83 ‘lumps’ p84 Epiphora p86 [3] Brain p87 Tumour p87 Infection p88 Movement disorders p89 Dementias p92 Cerebral blood flow p94 Epilepsy p95 Lung and Chest p98 Paediatric p113 Renal p122 Static p123 Dynamic p128 Reflux p136 Vascular p139 Radionuclide therapy p142 The Future p149 Statistics p152 Legal requirements p153 Patient information p154 Quiz p156 Suggested reading and websites p178 [4] INTRODUCTION Principles There are four basic methods of imaging the body, using x-rays, gamma rays, sound waves and magnetism. Each has its own place, and they are complementary, not exclusive. X-rays, whether as conventional images or as CT, provide anatomical information. X-rays (first discovered by Röntgen in 1895) are produced when electrons from the cathode in the x-ray tube hit the anode, usually made of tungsten mounted on steel, which is angled so that the x-rays leave the tube and can be collimated into a beam. The energy of the x-rays is a measure of their penetrating power – the higher the energy, the more penetrating. The beam is then collimated, and passes through the area of the body under investigation. The x-rays are absorbed by the tissues through which they pass, and the denser the tissue, the more are absorbed. Thus, at an x-ray energy of 85kV which is normal for diagnostic imaging, air absorbs none and bone absorbs all, with other tissues absorbing a variable amount. Thus a ‘shadowgraph’ emerges and it is this that is imaged on the x-ray film. In CT there is no film, rather an array of detectors, which pick up the attenuated beam and process it. X-RAY ADULT PELVIS – SEX OF PATIENT? [5] CT SCAN UPPER ABDOMEN In both the conventional image and the CT image, the differential attenuation allows visualisation of the tissues. In Nuclear Medicine studies, a carrier molecule is labelled with a radio-active tracer, usually 99mTc, and this is injected into the patient. Thus in this case it is the patient who is the source of the radiation, which are gamma rays, and they are emitted all around the patient. Another major difference is that x-rays are only produced from the tube when the machine is activated and the current flows through the x-ray tube, and the duration of current flow is set by the radiographer. When there is no current, there are no x-rays emitted. However, the gamma rays are emitted continuously, but decaying all the time. Isotopes have a half life (t1/2) which varies from isotope to isotope. This is the time required for the activity to 99m fall to 50%. Tc has a t1/2 of 6 hours. Nuclear Medicine studies, using gamma rays, provide physiological information. Conventional radiography, CT, US and MRI all provide anatomical information. The isotope and carrier used depend on the organ or system to be studied, and will be detailed later. This means that the Nuclear Medicine image will not necessarily be anatomically recognisable, although in the case of bone scans it often is. [6] NORMAL ADULT BONE SCAN – FAIRLY ANATOMICAL TOXIC THYROID NODULE – NOT ANATOMICAL AT ALL [7] A patient who has been injected with a radio-active tracer is slightly radio-active, but the activity is constantly falling, both due to the physical t1/2 of the isotope, but also due to breakdown and excretion of the carrier molecules (the biological t1/2). The effective t1/2 can be defined thus: 1/ t1/2 eff = 1/ t1/2phys + 1/ t1/2biol Nuclear Medicine can be used to image most parts of the body, but some organs are imaged much more than others. Risks For short t1/2 isotopes administered in normal diagnostic doses, there is no risk to either the patient or anyone else. It is important to inform the patients of this because they may otherwise worry needlessly, especially as a lot of people equate radiation with atom bombs, Chernobyl, and so on. With most straightforward diagnostic scans, as opposed to therapeutic administration of isotopes, radiation levels are well within the normal variation of background radiation, e.g. watching TV. Patients who have had a diagnostic scan can go near pregnant women or children without causing them any harm, and the same applies after treatment for benign diseases with isotopes such as 131I for thyrotoxicosis. Obviously, the patient cannot ask every woman they stand next to if she is pregnant! Whilst theoretically non-ionising radiation is safe for use during pregnancy, in practice only Ultrasound is used. In all other imaging situations, it is crucial to ask female patients between the ages of 12 – 55 about sexual activity, contraception and the likelihood of pregnancy. In minors, such questioning must be done tactfully, with a female chaperone on hand, and without the patient’s parents. Some isotopes are excreted via the kidneys and bladder, so in patients suffering from urinary incontinence, care must be taken not to contaminate their bedding, chairs and so on, even with short t1/2 isotopes. This is more important when 131 patients are treated with longer t1/2 isotopes such as I. X-rays and gamma rays are both examples of ionising radiation, in comparison with Ultrasound and MRI which are non-ionising and so do not (theoretically) cause any cellular damage, and are thus safer. The most widely used non-ionising radiation imaging is Ultrasound, in which sound waves are emitted from a transducer and reflected back in varying amounts from every anatomical interface, detected, and an image produced. Ultrasound waves are totally reflected by bone or calcium-containing structures such as gall stones, which appear white and cast an acoustic shadow behind them, and pass totally through liquid such as urine in the bladder, causing acoustic enhancement behind the structure. [8] The investigation takes place in real time, making the interpretation much easier for the operator. UPPER ABDOMINAL ULTRASOUND SHOWING LIVER AND KIDNEY MRI does not use ionising radiation, but rather a strong magnetic field to align all the hydrogen protons. The alignment is then disrupted by properly tuned RF pulses. As the protons recover their alignment, they emit radio signals and these can be measured and converted by Fourier transforms in a computer to produce an image. The machine is large with a long central tunnel, in which the patient is placed. The walls are very near the patient to ensure an even magnetic field. MRI BRAIN SHOWING ALTERED SIGNAL IN RIGHT PARIETAL AREA – STROKE [9] LATERAL MRI OF LUMBAR SPINE Both US and MRI show anatomical information, but recent advances in MR imaging (fMRI) allow physiological information to be obtained, particularly in the brain. Due to the intense magnetic field, care must be taken that no magnetic objects are in the room, and the patients have to complete a questionnaire prior to imaging. Such a check list is reproduced here. MRI PATIENT CHECKLIST Some items can interfere with the examination, some can be hazardous to your health. Please check the following list carefully. Answer all questions. Please do not hesitate to ask staff for help if you have any queries. NAME: ......................... ,............................................. DATE OF BIRTH: ....................................... WEIGHT: ..................................................... 1. Do you have a pacemaker, artificial heart valve or coronary stent? 2. Do you have aneurysm clips in your head (from a surgical procedure)? 3. Do you have any metal implants e.g. joint replacements, pins, wires? 4. Do you have a cochlear implant? 5. Do you have an artificial limb, calliper or surgical corset? 6. Do you have any shrapnel or metal fragments in your body? 7.