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Intracoronary injection of contrast media may cause significant disturbance of cardiac rhythm. Increased vagal activity may result in depression of the sinoatrial and atrio-ventricular nodes, causing bradycardia or asystole. The injection of a hypertonic contrast medium causes significant fluid and ion shifts. Immediately after injection there is a significant increase in serum osmolality.
This causes an influx of water from the interstitial space into the vascular compartment, an increase in blood volume, an increase in cardiac output and a brief increase of systemic blood pressure. Peripheral dilatation causes a more prolonged fall of blood pressure.
Injection into the right heart or pulmonary artery causes transitory pulmonary hypertension and systemic hypotension; injection into the left ventricle or aorta causes brief systemic hypertension followed by a more prolonged fall. In the presence of a high concentration of contrast medium, such as withdrawal of blood into a syringe of contrast medium, damage to red cell walls occurs and haemolysis follows.
Haemolysis and haemoglobinuria have been reported following angiocardiography. It is advisable not to re-inject blood that has been mixed with contrast medium.
Red cell aggregation and coagulation may occur in the presence of a high concentration of contrast medium, e. However, disaggregation occurs easily and this is not likely to be of any clinical significance. Contrast media impair blood clotting and platelet aggregation.
Low- and iso-osmolar contrast media have a minimal effect compared to HOCM. Contrast media have a potentiating effect on the action of heparin. Thrombus formation also occurs and is more common when blood is mixed with LOCM. However, the role of the syringe is also significant and thrombus formation is maximal when blood is slowly withdrawn into a syringe so that it layers on top of the contrast medium, against the wall of the syringe. Activation of coagulation by the tube material probably plays a significant role.
Contrast media have been shown to cause HbSS blood to sickle in vitro and sickle cell crisis has been provoked by contrast medium. Iso-osmolar contrast agents have a lesser effect and their use is indicated in this disease. When red blood cells are placed in a hypertonic contrast medium, water leaves the interior of the cells by osmosis and they become more rigid and less deformable. Isosmolar solutions may also have an effect on red cell deformability, indicating that there may also be a chemical effect.
Red cells that deform less easily are less able to pass through capillaries and may occlude them. This is the explanation for the transient rise in pulmonary arterial pressure during pulmonary arteriography and may also be a factor in contrast-induced nephropathy. Transient eosinophilia may occur 24ï¿½72 h after administration of contrast medium. In those affected, the serum creatinine concentration starts to rise within the first 24 h, reaches a peak by 2ï¿½3 days and usually returns to baseline by 3ï¿½7 days.
In rare cases patients may need temporary or permanent dialysis. There are a number of predisposing factors: 1. The most important risk factor is pre-existing impairment of renal function. Patients with normal renal function are at very low risk and those with GFR of mmol l-1 as an imperfect, but readily available, indicator of patients at increased risk of CIN. Dehydration is a risk factor. Age is also a factor because of the greater incidence of cardiovascular disease in the elderly.
Very large doses of contrast medium increase the risks. Multiple myeloma increases the risks. The presence of other nephrotoxic drugs is also a risk factor.
The mechanisms of CIN are summarized below 1. Impaired renal perfusion: a. Glomerular injury: a. Tubular injury: a. Obstructive nephropathy: a. However, clinical trials have so far yielded conflicting results. This is well recognized as a clinical problem with metformin, an oral hypoglycaemic drug which is exclusively excreted via the kidneys.
The resultant accumulation of metformin may result in the development of the potentially fatal complication lactic acidosis. See Table 2. Neurotoxicity is caused by both osmolality and chemotoxic effects and i. Thyroid function 1. Thyrotoxicosis may occur in patients with non-toxic goitres or be exacerbated in those with pre-existing thyrotoxic symptoms. Contrast media may interfere with thyroid function tests.
Major reactions, i. Intermediate reactions, i. Minor reactions, i. Minor and intermediate reactions are not uncommon; major adverse reactions are rare Table 2. Fatal reactions Deaths caused by iodinated contrast agents are very rare, occuring at a rate of 1.
Most are attributed to renal failure, anaphylaxis or allergic reaction. The fatal event may be preceded by trivial events, such as nausea and vomiting, or may occur without warning. The majority of deaths occur in those over 50 years of age.
Causes of death include cardiac arrest, pulmonary oedema, respiratory arrest, consumption coagulopathy, bronchospasm, laryngeal oedema and angioneurotic oedema. Flushing, metallic taste in the mouth, nausea, sneezing, cough and tingling are common and related to dose and speed of injection. Perineal burning, a desire to empty the bladder or rectum and an erroneous feeling of having been incontinent of urine are more common in women. Angioneurotic oedema.
Most commonly affects the face. May persist for up to 3 days and its onset may be delayed. Necrotizing skin lesions.
Rare and mostly in patients with preexisting renal failure particularly those with systemic lupus erythematosus. In most patients the bronchospasm is subclinical. Mechanisms include: a. Non-cardiogenic pulmonary oedema.
During acute anaphylaxis or hypotensive collapse and possibly due to increased capillary permeability. Usually accompanied by tachycardia but in some patients there is vagal over-reaction with bradycardia. The latter is rapidly reversed by atropine 0. Hypotension is usually mild and is treatable by a change of posture. Rarely, it is severe and may be accompanied by pulmonary oedema. Abdominal pain. May be a symptom in anaphylactic reactions or vagal overactivity. Should be differentiated from the loin pain that may be precipitated in patients with upper urinary tract obstruction.
Delayed-onset reactions ï¿½ 1 hï¿½1 week after injection include rashes, headaches, itching and parotid gland swelling. Risk factors for delayed reaction are previous contrast medium reaction and therapy with interleukin This could provide a mechanism for the phenomena of flushing, urticaria, metallic taste, hypotension, collapse and angioneurotic oedema. While hyperosmolality is a factor, isosmolar concentrations of contrast media will also stimulate histamine release.
Bronchospasm may be due to the effect of contrast medium on pulmonary-bed mast cells and dysrrhythmias from the effect on cardiac mast cells. Complement activation Contrast medium may activate the complement system leading to the formation of anaphylatoxins which induce the release of histamine and other biological mediators from basophils and mast cells. Protein binding, enzyme inhibition and immune receptors Contrast media are weakly protein bound and the degree of protein binding correlates well with their ability to inhibit the enzyme acetylcholinesterase.
Contrast medium side-effects such as vasodilatation, bradycardia, hypotension, bronchospasm and urticaria are all recognized cholinergic effects. It was previously thought that they might be related more to cholinesterase inhibition than osmolality; however, this has not been conclusively proven. More recently, it has been postulated that weakly protein bound drugs, such as iodinated contrast, may directly activate T cells which bear immune receptors.
It is thought that these may interact with the drug and that contrast medium may have an effect on cytokine production by helper T cells21 to mediate the acute reaction.
Chemotoxicity In addition to the toxicity of both ionic and non-ionic contrast media, because of their intrinsic structure, the ionic contrast agents had an electrical charge on the particles. This was almost certainly the cause of the high incidence of severe adverse reactions during intracoronary and intrathecal use of these agents. The high autonomic nervous system activity in an anxious patient will be stimulated further when the patient experiences the administration of contrast medium.
Furthermore, contrast medium crossing the bloodï¿½brain barrier can stimulate the limbic area and hypothalamus to produce further autonomic activity. This autonomic activity is responsible for contrast medium reactions by the sequence of events illustrated in Figure 2. From Lalli. Intravascular contrast media Table 2. The referring clinician should identify patients with pre-existing renal impairment and inform the radiology department. Serum creatinine should be measured within 1 week before the administration of contrast in patients: a.
Consider an alternative imaging method, not using iodinated contrast media. This should be withheld for a further 48 h after the procedure and renal function re-assessed before restarting metformin treatment. Use the smallest possible dose of contrast medium. Use low- or iso-osmolar contrast medium. There is insufficient evidence to support the use of prophylactic administration of N-acetyl cysteine for patients at high risk of contrast nephropathy.
There is no definite evidence that haemodialysis or peritoneal dialysis protect patients with impaired renal function from contrast medium induced nephrotoxicity. Patients with normal renal function on treatment with metformin: 1.
If ml of contrast is to be used intravenously or the intra-arterial route is to be used, the metformin should be withheld for 48 h after the procedure. If asthma not currently well controlled and examination is non-emergency, the patient should be referred back for appropriate medical therapy.
Precautions for patients at increased risk of anaphylactoid contrast reaction: 1. Consider an alternative test not requiring iodinated contrast. If the injection is considered necessary: a. Use a non-ionic low or iso-osmolar contrast agent b. For previous reactors to iodinated contrast use a different non-ionic low- or iso-osmolar contrast to that used previously c.
Maintain close supervision d. Leave the cannula in place and observe for 30 min e. Be ready to treat promptly any adverse reaction and ensure that emergency drugs and equipment are ready.
There are no conclusive data supporting the use of premedication in the prevention of severe reactions to contrast media in patients at increased risk and clinical opinion remains divided. Pre-treatment with antihistamines is of no benefit and is associated with an increased incidence of flushing. Pre-testing by applying contrast medium to the cornea or injecting a 1 ml test dose intravenously a few minutes prior to the full injection has also been abandoned. Other situations: Pregnancy ï¿½ In exceptional circumstances, iodinated contrast may be given.
Thyroid function of the neonate should be checked during the first week of life. Lactation ï¿½ No special precaution required. Breast feeding can continue normally. Thyrotoxicosis ï¿½ Intravascular contrast should not be given if the patient is hyperthyroid. Avoid thyroid radio-isotope tests and treatment for 2 months after iodinated contrast medium administration. Sickle cell anaemia ï¿½ There is risk of precipitating a sickle cell crisis. Iso-osmolar contrast should be used.
Myelomatosis ï¿½ Bence Jones protein may be precipitated in renal tubules. Risk diminished by ensuring good hydration. In patients at increased risk of reaction this should be increased to 30 min. Some aspects of synthesis of watersoluble contrast agents of low osmolality. Dawson, P. Katayama, H. Radiology 3 , ï¿½ Aspelin, P. Losco, P. Benko, A. Persson, P. Kidney Int. Liss, P. Brunette, J. Catheter Cardiovasc. Dillman, J. Palmer, F. Radiology , ï¿½ Wolf, G. Ionic contrast agents, ionic agents combined with steroids and nonionic agents.
Wysowski, D. Webb, J. Morcos, S. Lalli, A. Radiology 2 , ï¿½ BMJ , Intravascular contrast media Thomsen, H. In , Carr et al. To enhance the inherent contrast between tissues, MRI contrast agents must alter the rate of relaxation of protons within the tissues. The changes in relaxation vary and, therefore, different tissues produce differential enhancement of the signal see Figs 2. These figures show that, for a given time t, if the T1 relaxation is more rapid then a larger signal is obtained brighter images , but the opposite is true for T2 relaxation, where more rapid relaxation produces reduced signal intensity darker images.
There are different means by which these effects on protons can be produced using a range of MRI contrast agents.
MRI contrast agents must exert a large magnetic field density a property imparted by their unpaired electrons to interact with the magnetic moments of the protons in the tissues and so shorten their T1 relaxation time which will produce an increase in signal intensity see Fig. The electron magnetic moments also cause local changes in the magnetic field, which promotes more rapid proton dephasing and so shortens the T2 relaxation time. Agents with unpaired electron spins are potential contrast agents in MRI.
These retain magnetism even when the applied field is removed. This may cause particle aggregation and interfere with cell function, making them unsafe for clinical use as MRI contrast agents. Intravascular contrast media 2. Paramagnetic ï¿½ e. These contrast agents have magnetic moments which align to the applied field, but once the gradient field is turned off, thermal energy within the tissue is enough to overcome the alignment. Gadolinium compounds may be made soluble by chelation and can, therefore, either be injected intravenously or used as an oral preparation.
Their maximum effect is on protons in the water molecule, shortening the T1 relaxation time and hence producing increased signal intensity white on T1 images Fig. Superparamagnetic ï¿½ e. These cause abrupt changes in the local magnetic field which results in rapid proton dephasing and reduction in the T2 relaxation time, and hence producing decreased signal intensity black on T2 images Fig.
Superparamagnetic compounds were initially produced only as large particles in a colloid suspension for gastrointestinal contrast. Extracellular fluid ECF agents: by far the most commonly used form of gadolinium. They all contain gadolinium, an 8-coordinate ligand binding to gadolinium and a single water molecule coordination site to gadolinium and all have a molecular weight similar to iodinated contrast agents.
After intravenous injection they circulate within the vascular system and are excreted unchanged by the kidneys. The ECF agents do not cross the normal bloodï¿½brain barrier but do cross the abnormal bloodï¿½brain barrier. ECF agents are used for angiography but rapidly leak out of the vascular space into the interstitial space so are used only for dynamic arterial studies. There is a wide range of indications for these contrast media including improved detection rates and more accurate delineation and characterization of tumours.
These agents are used to improve detection of liver lesions which do not contain hepatocytes therefore do not take up the contrast , such as liver metastases, and to characterize lesions which do take up the contrast, such as hepatocellular carcinoma. They can also be used to provide positive contrast T1 weighted of the hepato-biliary system. Blood pool agents: the blood pool agents remain longer in the vascular space than ECF agents and allow a wider range of vascular imaging.
The first of these contrast agents approved for clinical use in Europe, gadofosveset trisodium Vasovist, Bayer Schering ,2 has recently been introduced. Dose For ECF gadolinium agents, usually 0.
Adverse reactions Gadolinium contrast agents are very safe and well tolerated; they have a much lower incidence of adverse reactions than iodinated contrast agents. Adverse reactions to gadolinium are mostly mild and self-limiting and can be divided into acute and delayed reactions.
The incidence is shown in Table 2. Acute adverse reactions These are rare, but the following have been described: 1. Table 2. Renal impairment ï¿½ when used at the standard doses given above, gadolinium contrast agents do not cause significant impairment of renal function. It was initially thought that gadolinium agents might be used as a replacement for iodinated contrast for those at increased risk of contrast nephrotoxicity.
However, when used at the high doses required to give equivalent X-ray attenuation, gadolinium-based contrast media have more nephrotoxic potential than iodinated contrast. Nephrogenic systemic fibrosis NSF ï¿½ this systemic disorder, first described in , is characterized by increased deposition of collagen with thickening and hardening of the skin, contractures and, in some patients, clinical involvement of other tissues.
The mechanism by which renal failure and gadolinium-based contrast agents trigger NSF is not known. The overwhelming majority of reported cases of NSF represent patients who had previously been given gadodiamide Omniscan, GE Healthcare ,10 but there are some reports of NSF associated with other gadolinium contrast agents.
Acute adverse reactions 1. Identify patients at increased risk of reaction because of previous gadolinium reaction, asthma, allergies or previous adverse reaction to iodinated contrast.
For those at increased risk consider an alternative test not requiring a gadolinium agent. If proceeding with i. Delayed adverse reaction: 1. End holes: 1 Side holes: 0. Heart Figure 8. End holes: 0 Side holes: 4 or 6. Figure 8. End holes: 1 Side holes: Right-sided cardiac structures and pulmonary arteries are examined by introducing a catheter into a peripheral vein.
In babies the femoral vein may be the only vein large enough to take the catheter. If an atrial septal defect is suspected, the femoral vein approach offers the best chance of passing the catheter into the left atrium through the defect.
In adults the right antecubital or basilic vein may be used. The cephalic vein should not be used because it can be difficult to pass the catheter past the site where the vein pierces the clavipectoral fascia to join the axillary vein. The catheter, or introducer, is introduced using the Seldinger technique. The NIH catheter must be introduced via an introducer as there is no end hole for a guidewire.
In children it is usually possible to examine the left heart and occasionally the aorta by manipulating a venous catheter through a patent foramen ovale. In adults the aorta and left ventricle are studied via a catheter passed retrogradely from the femoral artery. The catheter is manipulated into the appropriate positions for recording pressures and sampling blood for oxygen saturation. Following this, angiography is performed.
Alignment of the heart perpendicular to the X-ray beam. Further rotation of the direction of the X-ray beam is used to profile those areas of the heart under examination. Useful views are: 1. Diagnosis of the presence and extent of ischaemic heart disease After revascularization procedures Congenital heart lesions Therapeutic percutaneous coronary intervention ï¿½ balloon angioplasty and stenting. Heart Diagnostic arteriography can be supplemented by intravascular ultrasound US to determine the nature and extent of plaque within the vessel wall or angioscopy in some centres.
Contrast medium LOCM , 8ï¿½10 ml given as a hand injection for each projection. Equipment 1. Digital angiography with C-arm 2. Pressure recording device and ECG monitor 3. Judkins Fig. Patient preparation As for routine arteriography. Preliminary image Chest X-ray.
End holes: 1 Side holes: 0 Left Right Figure 8. With femoral puncture: as above. Left coronary artery 1. With femoral puncture: additional lateral projection possible. Complications In addition to the general complications discussed in Chapter 9, patients undergoing coronary arteriography may be liable to: 1. Arrhythmias ï¿½ such as non-sustained atrial fibrillation with right heart catheterization or non-sustained ventricular arrhythmia with left ventriculography 2.
Ostial dissection by the catheter 3. Access site complications ï¿½ local haematoma, femoral artery pseudoaneurysm or arterio-venous fistula. Mostly with femoral route. This is the result of fast scan times and cardiac gating facilities available with multidetector CT scanners. Whilst the examination is tailored to assessment of the cardiac structures, CT imaging gives the benefit over conventional cardiac and coronary angiography of demonstrating clinically significant noncardiac findings within the adjacent mediastinum, lungs or upper abdomen,1 and can give additional information regarding plaque characterization.
Cardiac CT may be performed as: Heart 1. Unenhanced CT scan for coronary artery calcium scoring 2. Contrast enhanced CT for myocardial assessment or cardiac valve imaging specialist centres only. The coronary artery calcium CAC score is calculated from the volume of calcium present in the coronary arteries.
A high score indicates an increased risk of adverse coronary events and CAC scoring has been used as a screening tool for subclinical cardiac disease. Absence of coronary artery calcification does not exclude atheroma but is associated with a low risk of adverse coronary event. Evidence shows that scores will probably need to be matched to age, sex and ethnic background.
Tailored coronary CTA is well-documented to have a high negative predictive value for coronary artery stenosis. Patients with known or suspected chronic coronary artery disease. As a screening test in asymptomatic high-risk patients or patients with atypical chest pain. As an alternative to diagnostic coronary angiography when planning percutaneous angiographic intervention or as post-procedure follow-up.
Visualization of coronary artery grafts, including the entire course of the left internal mammary artery LIMA graft to its distal anastomosis on the coronary artery. Each CT manufacturer will advise scan protocols tailored to their specific scanners; however, general parameters useful for coronary artery assessment cardiac CT are as follows:7 1.
For optimal imaging, the patient should have a regular heart rate of 50ï¿½65 beats per minute during the scan. Either oral or intravenous i. The saline chase reduces streak artifact from dense contrast in the right side of the heart, whilst the right-sided cannulation reduces streak artifact from the left subclavian artery or internal mammary coronary graft.
An initial unenhanced scan is sometimes used to assess the coronary artery calcium score, provide landmarks for planning of the contrast run and allow the patient to become accustomed to the scan.
Delay: a. Preset delay of 18ï¿½20 s OR, preferably, b. Bolus tracking using software supplied with the multidetector scanner. A ROI region of interest is positioned over the ascending aorta. Image review using axial scans, multiplanar reconstructions MPR , curved MPRs, volume rendering and surface shaded display all useful to analyse the vessel pathway, wall and caliber.
Weinreb, J. Preis, S. Heart 3. Mahesh, M. RadioGraphics 27, ï¿½ Coles, D. Abdulla, J. Heart J. Nieman, K. Cademartiri, F. Circulation , ï¿½ Schoepf, U. Radiology , 48ï¿½ Earls, J. Pugliese, F. Further reading Gershlick, A.
Heart 93, ï¿½ Vanhoenacker, P. Evaluation of ventricular function; particularly left ventricular ejection fraction LVEF 2. Assessment of myocardial reserve in coronary artery disease 3. Cardiomyopathy, including the effects of cardio-toxic drugs. First pass radionuclide angiography 2,3 1. Evaluation of right ventricular ejection fraction RVEF 2. Detection and quantification of intra-cardiac shunts. The stannous ions reduce the pertechnetate and allow it to bind to the pyrophosphate which adsorbs on to the red blood cells.
Gamma-camera: equipped with low-energy general purpose collimator 2. Imaging computer: list-mode or multi-gated acquisition MUGA 3. ECG monitor with gating pulse output. Patient preparation 1. Avoid injection via long plastic Teflon coated cannula which may result in a poor label. Three ECG electrodes are placed in standard positions to give a gating signal. Technique Gated blood-pool study 1. List mode is best, where individual events are stored as their x, y coordinates along with timing and gating pulses.
This allows maximum flexibility for later manipulation and framing of data. Around 5 million counts should be acquired. However, MUGA mode is adequate, and is still the most commonly used.
A series of 16ï¿½32 fast frames are recorded before the next R wave occurs. Each of these has very few counts in from a single cycle, so every time the R wave trigger arrives another set of frames is recorded and summed with the first. The sequence continues Heart until ï¿½ kilo-counts per frame have been acquired in about 10 min. The length of time to acquire an image set increases as the proportion of rejected beats rises.
First-pass radionuclide angiography This provides information on right ventricular function and intracardiac shunts, although only from one view unless a multi-headed camera or bi-planar collimator is available: 1. Positioning depends upon the clinical question. For assessment of shunting, the camera is positioned anteriorly. The ECG trigger signal is connected. The validity of the first-pass study is dependent on the quality of the bolus injection.
For RVEF assessment, the 99mTcpertechnetate is injected over approximately 3 s too tight a bolus will not provide sufficient cardiac cycles for evaluation; too slow an injection will result in poor image statistics before circulation through the lung capillary bed and left side of the heart.
However, for shunt quantification, 99mTc-pertechnetate is injected in as tight a bolus as possible by using the Oldendorf or similar technique see Chapter 1. Gated list-mode computer acquisition is started as the bolus is released. Although the first pass usually takes a maximum of 10ï¿½15 s, it is advisable to continue data acquisition for up to 50 s in case of slow bolus arrival.
A gated blood-pool study follows, as above. Patient supine. Anterior, patient supine 3. LPO, chosen to give best separation between atria and ventricles. Patient in right lateral decubitus position. Analysis Gated blood-pool study 1. The LVEF is calculated 2. Systolic, diastolic, phase and amplitude images are generated 3. The frames can be displayed in cine mode to give good visualization of wall motion. First-pass study 1. The RVEF can be calculated 2. Serial images can be produced showing the sequence of chamber filling 3.
A time-activity curve from the pulmonary region can be used for quantitative assessment of a shunt 4. Chamber transit times may be calculated. Additional techniques 1. Gated blood-pool imaging can be carried out during controlled exercise with appropriate precautions to assess ventricular functional reserve. Leg exercise using a bed-mounted bicycle ergometer is the method of choice.
Shoulder restraints and hand grips help to reduce upper body movement during imaging. For patients unable to exercise effectively, stress with dobutamine infusion is used. Monitor recovery from exercise 2. Normal radiation safety precautions see Chapter 1. Heart Complications Complications are related to the exercise test and include induction of angina, cardiac arrhythmias and cardiac arrest. Metcalfe, M. In: Sharp, P.
London: Springer. Friedman, J. Williams, K. Konishi, T. Fukuoka, S. Anagnostopoulos, C. Diagnosis and assessment of extent and severity of myocardial ischaemia or infarction 2. Assessment of myocardial viability 3. Evaluation of prognosis 4.
Evaluation of effects of angioplasty and bypass surgery on myocardial perfusion with pre- and post-intervention imaging. Contraindications 1. Unstable angina Frequent ventricular arrhythmias at rest Contraindications to pharmacological stress agent Second-degree heart block Severe valvular disease, especially aortic valve stenosis. Cationic complex with myocardial uptake in near proportion to coronary blood flow but minimal redistribution. There is also, normally, liver uptake and biliary excretion, which can cause inferior wall artifacts on SPECT if care is not taken.
Thallium is a potassium analogue with initial rapid myocardial uptake in near proportion to coronary blood flow, and subsequent washout and redistribution. It is increasingly being replaced by 99mTc agents. However, many still consider Tl for assessment of myocardial viability and hibernation, with either re-injection at rest or a separate day rest-redistribution study giving the greatest sensitivity. The radio-isotope gold standard for viability assessment, but not widely available3 Rubidium PET.
This study can be used to assess myocardial perfusion. Not widely available. SPECT-capable gamma-camera, preferably dual-headed 2. Low-energy, high-resolution, general purpose or specialized cardiac collimators 3. Pharmacological stressing agent adenosine, dipyridamole or dobutamine or exercise bicycle ergometer or treadmill 4. Nitroglycerin tablets or sublingual spray to enhance resting uptake of ischaemic, but viable segments 5.
ECG monitor 6. Resuscitation facilities including defibrillator 7. Aminophylline to reverse possible severe bronchospasm after dipyridamole infusion 8. Lidocaine to reverse serious arrhythmias caused by dobutamine infusion Heart Patient preparation 1.
Nil by mouth or light breakfast 4ï¿½6 h prior to test 2. Cessation of cardiac medication on the day of the test if possible. Avoid caffeine for 24 h if using dipyridamole or adenosine. Technique The principal of the technique is to compare myocardial perfusion under conditions of pharmacological stress or physical exercise, with perfusion at rest.
Diseased but patent arterial territories will show lower perfusion under stress conditions than healthy arteries, but will show relatively improved perfusion at rest. Infarcted tissue will show no improvement at rest. Hence, prognostic information on the likelihood of adverse cardiac events and the benefits of revascularization can be gained. The preferred pharmacological stressing agent is adenosine infusion 0.
It reproducibly increases coronary artery flow by more than maximal physical exercise which often cannot be achieved in this group of patients. It has a short biological half-life of 8ï¿½10 s, so most side-effects are reversed simply by discontinuing infusion. Stressing with adenosine has now largely replaced dipyridamole, which will not be discussed here. There are circumstances where adenosine is contraindicated, e. Dobutamine is contraindicated in patients with aortic aneurysm.
New, more specific targeted agents such as regadenoson A2A adenosine receptor agonist are being developed which could be used in asthmatic patients rather than dobutamine. Two-day protocols are optimal, but it is often more convenient to perform both studies on the same day. Initiate pharmacological stress or exercise 2.
Images are acquired 15ï¿½30 min after tetrofosmin or 60ï¿½ min after sestamibi injection. If there is excessive liver uptake or activity in small bowel close to the heart, imaging should be delayed by a further 60 min 5.
Depending on the clinical situation, if the stress scan is completely normal the patient may not need to return for the rest scan10 6. Preferably 2ï¿½7 days later, the patient returns for a resting scan 7. Glyceryl trinitrate GTN two 0. Image as per 2-day protocol 3. A minimum of 2 h after first tetrofosmin injection and minimum of 4 h after sestamibi injection, GTN is administered as above, followed by up to MBq MIBI or tetrofosmin with longer period between injections, the activity of the second injection may be reduced 4.
Image as per 2-day protocol. Administer 80 MBq Tl i. Image immediately 8. Fasting for 4ï¿½6 h, with plenty of non-sugary fluids 2. Monitor blood glucose before injection to ensure it is not elevated.
Elevated blood glucose levels result in diversion of glucose to muscle. Consider rescheduling patient if blood glucose elevated. Administration of insulin is counterproductive as this diverts glucose uptake to muscle 3.
A mild sedative such as diazepam may be given to reduce physiological muscle and brown fat uptake 4. Oral contrast may be administered to aid interpretation of the CT. Attenuation correction artifact on the PET images secondary to the high-density contrast has been shown not to be clinically significant.
To reduce muscle uptake of FDG, patients should remain in a relaxed environment such as lying in a darkened room without talking if head and neck area are being imaged between injection and scan.
Image at 1 h post injection. Later imaging has been reported to enhance tumour conspicuity due to a higher tumour to background ratio.
Imaging is preferred with the arms above the head to reduce beam hardening artifact on the CT. CT: a. Low dose b. Positive or negative oral contrast agents according to local protocol are increasingly being used. PET: a. From the base of skull to upper thighs occasionally extended if melanoma or limb or head and neck tumours b. In some instances a diagnostic standard dose CT with i.
Other applications Coronary artery disease Chapter 8 Assessment of myocardial viability. Location of epileptic foci 2. Assessment of dementia. Kapoor, V. RadioGraphics 24 2 , ï¿½ Rohren, E. Indications 1. Gallium imaging has been used with variable success in a variety of other tumours, e.
It has also been used in benign conditions such as sarcoidosis and for localization of infection or in suspected orthopaedic infection 11 Contraindications None. Normal accumulation is seen in the liver, bone marrow and nasal sinuses, and variably in the spleen, salivary and lacrimal glands. There is significant excretion via the gut and some via the kidneys.
Gamma camera, preferably with whole-body and single-photon emission computed tomography SPECT facilities 2. Medium- or high-energy collimator. Patient preparation If the abdomen is being investigated, laxatives may be given if not contraindicated for 2 days after injection of 67Ga-citrate to clear bowel activity. Additionally, an enema or suppository may be given on the day of imaging. Delayed images are acquired as below with energy windows about the lower two or all three of the main photopeaks.
Images 1. SPECT can increase the sensitivity and specificity of the investigation 2. Non-specific bowel activity can be discriminated by imaging on two separate occasions. Activity in bowel contents should move between scans and abnormal areas of accumulation will be stationary.
If there is still any doubt at 72 h, later images at up to 7 days may prove helpful. A radionuclide bone scan may be performed prior to gallium imaging. A radiocolloid scan may help to discriminate between lesions in the region of the liver or spleen and normal uptake in these organs. Image subtraction techniques may be used. Aftercare Normal radiation safety precautions.
Complications None. Seam, P. Blood 10 , ï¿½ Lymph glands, lymphatics and tumours Further reading Bombardieri, E. Front, D. It is taken up actively across cell membranes of sympathetic and adrenal medullary tissue into intracellular storage vesicles. There is no further metabolism, and it remains sequestered and localized in the storage vesicles of catecholamine-secreting tumours and tumours of neuroendocrine origin.
Neuroblastoma Phaeochromocytoma Carcinoid tumours Medullary thyroid carcinoma Other neuroendocrine tumours. Contraindications 11 None. Radiopharmaceuticals 1. The h half-life of I allows imaging up to 48 h 2. However, the higher photon energy of the emitted gamma rays renders it an inferior imaging agent and results in a higher radiation dose to the patient. Low-energy general purpose collimator for I. Where possible, stop medications that interfere with MIBG uptake.
Thyroid blockade, to reduce radiation dose to the thyroid continuing for 24 h after I-MIBG injection: a. Adults ï¿½ either oral potassium perchlorate mg, 1 h before MIBG injection, then mg every 6 h or oral potassium iodate 85 mg twice daily starting 24 h before MIBG injection b.
Potassium iodate is more palatable ï¿½ the tablets need splitting for paediatric dosage. MIBG is administered slowly i.
Imaging at 24 h sometimes additionally at 4 or 48 h , emptying bladder before pelvic views. Anterior and posterior abdomen, 10ï¿½20 min per view 2. Whole-body imaging for comprehensive search for metastases 3.
SPECT may help to localize lesions, particularly in thorax and abdomen. If therapy with I-MIBG is being considered, quantitative assessment can be performed using geometric mean and attenuation correction to calculate percentage of administered dose residing in tumour at 24 h. It appears to be more sensitive for carcinoids, and may be useful in cases where the MIBG scan is negative.
It also has therapeutic analogues under development. Lymph glands, lymphatics and tumours Aftercare Normal radiation safety precautions see Chapter 1. Ilias, I. Solanki, K.
Octreotide a long-acting analogue of the human hormone, somatostatin can be used therapeutically to inhibit hormone production by carcinoids, gastrinomas and insulinoma, etc. A number of tumours, particularly those of neuroendocrine origin, express neuroendocrine receptors.
Imaging after the administration of radionuclide-labelled somatostatin analogues such as octreotide, therefore, allows their localization. Although sometimes used for the assessment of insulinomas, these latter tumours are more variably visible with octreotide approx. ED 17 mSv. Medium energy for In. Some centres use bowel preparation 2. Oral hydration to help with renal clearance. There is usually high renal uptake 3.
In patients with possible insulinoma i. Discontinue oral somatostatin to avoid competitive inhibition. Technique Image at 24 h and 48 h if necessary: 1. Additional techniques MIBG may be positive in octreotide negative tumours and vice versa. Aftercare Normal radiation safety precautions see Chapter 1. Krenning, E. Directly: a. Indirect evidence from displacement of normal structures, e. Non-invasive and without risk to the patient 2.
Helpful in the neck and axilla in particular, especially with Doppler analysis and US-guided fine-needle aspiration or core biopsy Disadvantages: 1. Highly operator-dependent 2. Intestinal gas is a major factor in poor visualization.
Unsuitable for the mediastinum. Advantages: 1. Can image all nodes 2. Technically easy to perform. Disadvantages: 1. Internal structure is not seen 2. Gives no indication of nature, apart from on the basis of size, and possibly on basis of enhancement characteristics. Gives no indication of nature, apart from on the basis of size. Nodes containing malignant tissue retain their high signal intensity on the post contrast scans and small tumour deposits can be detected in even normal-sized nodes.
Lipiodol, the usual contrast material, is no longer available and operator expertise is also largely no longer available. High-resolution anatomical detail is not possible.
In recent years, this has become the major indication for lymphoscintigraphy. The technique in itself does not diagnose nodes affected by malignancy; rather it identifies the node most likely to be involved and, therefore, to allow histological sampling. Differentiation of lymphoedema from venous oedema 3. Assessment of lymphatic flow in lymphoedema. Lymph glands, lymphatics and tumours Radiopharmaceuticals 1.
Radiopharmaceuticals Fluorine fluorodeoxyglucose 18FDG is a glucose analogue which is the most commonly used agent for oncological work and is also used for the investigation of dementias.
There are other radiopharmaceuticals, e. Patient preparation Fasting for 4ï¿½6 h, with plenty of non-sugary fluids. To reduce muscle uptake of 18FDG, patients should remain in a relaxed environment such as lying in a darkened room, without talking if head and neck area are being imaged, between injection and scan. If combined with CT scanning: a. PET imaging of: a. Brain Alternative techniques 1. Thallium 3.
All chapters have been thoroughly reviewed and, where appropriate, revised and rewritten to reflect current radiological practice, and a new chapter on patient consent has been added. As always, it is a difficult balance to ensure that current radiological practice is faithfully reflected but not to dismiss older techniques which may still be used in some centres or may continue to be required where there are contraindications to current preferred techniques such as MR imaging.
It has been a great privilege to be involved with this Guide; the 2nd edition of which rarely left my side as a junior radiologist.
I hope the book continues to be a valued resource for the current generation of radiology trainees. If you found this book helpful then please like, subscribe and share. Friday, February 10, Sign in. Forgot your password? Get help. Create an account. Password recovery.
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Reflects changes in examination.
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