Diagnostic arteriography can be supplemented by intravascular ultrasound (US) to determine the nature and extent of plaque within the vessel wall and, in some centres, with angioscopy. Pressure wire studies to determine fractional flow reduction (FFR) across stenoses prior to angioplasty/stenting can be performed; particularly useful in assessment of intermediate lesions.

Contrast medium

LOCM 370 mg I ml^–1, 8–10 ml given as a hand injection for each projection.

Equipment

1. Digital angiography with C-arm

2. Pressure recording device and ECG monitor

3. Selective coronary artery catheters:

(a) Judkins (Fig. 8.4) or Amplatz (Fig. 8.5) catheters – the left and right coronary artery catheters are of different shape. These can be used for both femoral or radial approaches (usually utilizing smaller Judkins for the left coronary artery)

Figure 8.4 Judkins coronary artery catheters. End holes: 1 Side holes: 0.

Figure 8.5 Amplatz coronary artery catheters. End holes: 1 Side holes: 0.

(b) Tiger II catheter (Fig. 8.6) – specifically designed for right radial approach. Single catheter used for both left and right coronary arteries (reduces procedure time, radiation exposure and less manipulation leading to less radial artery spasm)

Figure 8.6 Tiger II coronary artery catheter. End holes: 1 Side holes: 0.

Patient preparation

As for routine arteriography.

Preliminary image

Chest X-ray.

Technique

The catheter is introduced using the Seldinger technique via the radial (most commonly), brachial or femoral artery and advanced until its tip lies in the ostium of the coronary artery.

Image acquisition

Optimum visualization of vessels is obtained with images acquired perpendicular to the vessel under examination so multiple, compound projections using rotation around the patient axis as well as cranio-caudal angulations of the X-ray beam are utilized for each coronary vessel.

Angiography (7.5 frames s^–1) is performed in the following projections:

1. Right coronary artery*

• RAO 30°

• LAO 30°

• LAO 30°/cranial 30°

2. Left coronary artery*

• PA

• LAO 45°/caudad 30° (‘spider view’)

• RAO 45°/caudad 30°

• RAO 45°/cranial 30°

• LAO 45°/cranial 30°

(* though each projection will show good visualization of various segments of the other coronary artery).

Complications

In addition to the general complications discussed in Chapter 9, patients undergoing coronary arteriography may be liable to:

1. Arrhythmias – 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 (more commonly seen with femoral approach) – local haematoma, femoral artery pseudoaneurysm or arterio-venous fistula.

Indications

1. Patients with known or suspected chronic coronary artery disease

2. Assessment of suspected anomalous coronary artery anatomy

3. As a screening test in symptomatic patients with typical chest pain but a low clinical probability of significant coronary artery disease

4. As a screening test in asymptomatic but high-risk patients or patients with atypical chest pain

5. Assessment of coronary artery grafts, including left internal mammary artery (LIMA) grafts

6. As an alternative to diagnostic coronary angiography when planning percutaneous angiographic intervention or as post-procedure follow-up.

7. Assessment of left atrium and pulmonary vein anatomy prior to electrophysiological studies and ablation.

Contraindications

1. Standard contraindications to iodinated contrast media administration – previous significant contrast reaction, renal insufficiency, etc.

2. Inability to lie still, breath hold or cooperate with scan instructions

3. Clinical instability

(a) Cardiac failure, acute myocardial infarction, severe hypotension

(b) Cardiac dysrhythmia: including atrial fibrillation, frequent ventricular extrasystoles and bigeminy

Patient preparation

1. Avoid caffeine – this includes tea, coffee and caffeine-containing soft drinks (including ‘decaffeinated’ varieties), ‘energy’ pills and Viagra-type medication.

2. Drugs – patients should take all their normal cardiac medication as usual on the day of the test.

3. Thorough explanation of the procedure to the patient aids compliance, particularly with regard to breath-hold (suggest patient takes a ‘ breath’ when instructed – less likely to move during scan and avoids ‘Valsalva’ manoeuvre affecting contrast bolus entering chest).

4. 18G cannula in right antecubital fossa – siting cannula in right arm reduces artefact as contrast crosses the mediastinum. For graft studies this avoids streak artefact obscuring origin of LIMA grafts.

5. Assess suitability for administration of β-blockers and sublingual nitrates (see below).

Beta-blockers

Optimal imaging quality and radiation dose are significantly influenced by heart rate, which ideally should be between 55–65 bpm. With basic precautions and simple monitoring, safe and dose-titratable heart rate reduction can be achieved in the majority of patients using β-blocker administered within the radiology department. Metoprolol is commonly used and can be given orally or intravenously, or in combination.

• The patient may already be on oral β-blockers (either as regular medication or specifically prescribed by the referrer for the purposes of the examination). In most cases the scan can proceed without further medication.

• If the patient is not on β-blockers, requires heart rate reduction to optimize scan and has no contraindication to β-blocker administration, metoprolol can be given orally or i.v.

(Contraindications to β-blockade include heart failure, significant aortic stenosis, heart block, asthma/COPD, use of other antiarrhythmic medication including calcium channel blockers and digoxin.)

• Metoprolol 100 mg orally 1 h prior to scan. Pulse and blood pressure monitored regularly until heart rate reaches desired level. (If the heart rate does not reach a satisfactory level additional metoprolol can be given intravenously whilst the patient is on the scanner.)

• Metoprolol can be given solely in i.v. form (or to ‘top up’ oral dose where optimal heart rate has not been achieved with oral administration) just before the start of the scan with the patient on the scanner table. 5–30 mg i.v. given in aliquots of 5 mg titrated against heart rate.

Nitrates

Sublingual glyceryl trinitrate 400–800 µg (1–2 tablets) can be given a few minutes prior to scanning to produce coronary dilatation and improve image quality. Temporary effect of hypotension is unlikely to be an issue with the patient lying on the CT table and transient physiological elevation of heart rate usually resolves by the time of image acquisition. (Contraindications to nitrates include: hypotension, hypovolaemia, severe aortic valve stenosis, hypertrophic cardiomyopathy, recent MI, severe anaemia, recent ‘Viagra’-type medication.)

Technique

Cardiac CT remains a high radiation dose procedure and careful attention to dose reduction measures, whilst maintaining image quality, is essential. The use of ‘prospective’ rather than ‘retrospective’ scanning and, where possible, single heart beat acquisition reduce radiation dose very significantly.

Scan technique will be determined by the clinical question to be answered and by patient heart rate; the exact protocol will be determined by the manufacturer and model of the CT scanner.

Scan protocol

All scans are ECG-gated (a) to allow retrospective reconstruction of images timed to specific points in the cardiac cycle, (b) where possible, to allow prospective ECG triggering of the scan with X-ray exposure only during specific parts of the cardiac cycle (usually mid-late diastole to derive coronary artery images) or (c) if prospective triggering is not possible, to modulate the tube current – by decreasing X-ray exposure during parts of the cardiac cycle where image quality is not so critical (usually systole and early diastole) to reduce overall radiation dose.

Plain CT heart

Prospective ECG-triggered non-contrast scan acquired during diastole (usually c. 65–80% of R–R interval) over 3–4 cardiac cycles. Used to detect and quantify coronary artery calcification from which the age- and sex-matched Calcium Score is calculated. Higher scores are associated with increasing risk of significant atheromatous disease and the technique can be used as a screening tool for subclinical cardiac disease. Absence of coronary artery calcification however does not completely exclude atheroma but is associated with a low risk of adverse coronary event. The plain scan can then be used to plan the range of the subsequent contrast-enhanced scan.

Contrast-enhanced cardiac scan

Contrast administration

The rapidity of the scan acquisition necessitates very accurate timing of contrast bolus to ensure optimal vessel opacification (but also means that generally smaller volumes of contrast medium can be utilized). Biphasic injection of contrast followed by saline ‘chaser’ (or if desired, diluted contrast) improves geometry of delivery of contrast and ‘washes out’ the right side of the heart to reduce streak artefact. Typically 90–100 ml LOCM 350 mg I ml^–1-given at 5–7 ml s^–1 followed by 40–50 ml saline at 4–7 ml s^–1. Graft studies need higher volume of contrast 100–120 ml LOCM 350 mg I ml^–1 at 5–6 ml s^–1.

Bolus timing can be achieved using:

1. Empirical delay of c. 25 s. Unreliable and not recommended

2. ‘Bolus-tracking’ – a selected region-of-interest (ROI) – usually ascending aorta – is scanned every second or so following contrast injection and the full acquisition scan is automatically triggered (after a short delay) once the ROI has enhanced to a preset level e.g. 120 HU

3. ‘Test bolus’ – a small initial injection of contrast (e.g. 20 ml contrast with 40 ml saline ‘chaser’ bolus) is given and the ROI (ascending aorta) is scanned and time-to-peak enhancement is derived. The full scan is then performed using this timing delay. (Usually add 3 s to allow for maximal coronary vessel enhancement). This method is probably the most reliable and accurate, confirms i.v. line patency and familiarizes the patient ready for the final crucial acquisition scan.

Retrospective scan

Helical acquisition throughout the cardiac cycle. Retrospective reconstruction of images from data acquired during diastole (c 75% of RR) to show coronary and cardiac structures and from entire data set to show functional imaging of entire cardiac cycle. This is a high radiation dose procedure (approximately 14 mSv) and is utilized in patients with higher heart rates, less stable heart rhythms, for graft assessment and in patients where functional data from the whole cardiac cycle is required. Modulation of tube current in systole and early diastole should be used whenever possible to decrease overall radiation dose (by up to 50%) – image quality is reduced during these less critical parts of the cardiac cycle but useful functional data are preserved.

Prospective scan

ECG-gated prospective triggered sequential axial scan X-ray exposure is limited to specific part of cardiac cycle acquiring data over successive heart beats. Usually centred at approximately 75% of R–R interval in mid/late diastole in order to optimally image the coronary arteries. Requires careful patient selection and preparation; low heart rate and regular rhythm and does not acquire any data from other parts of the cardiac cycle, i.e. no functional information is obtained. Dose reduction of up to 90% compared to retrospective acquisition (currently 2–4.5 mSv – comparable to conventional catheter angiogram c. 5 mSv).

Single-beat acquisition

Using advanced CT technology, acquires data from whole heart in a single cardiac cycle using either wide-area detector covering whole volume of heart or dual-source high-pitch helical acquisition. Requires cooperative patient, low heart rate and very stable rhythm but offers potential of low radiation dose approaching 1 mSv and reduced contrast media volume.

Indications

1. Assessment of chamber dimensions, mass and function

2. Assessment of complex congenital heart disease

3. Diagnosis and evaluation of cardiomyopathies – e.g. sarcoid, amyloid, hypertrophic cardiomyopathy, arrhythmogenic right ventricular cardiomyopathy

4. Evaluation of cardiac masses

5. Evaluation of pericardial disease

6. Evaluation of:

(a) myocardial viability

(b) extent of myocardial necrosis/fibrosis

7. Imaging and quantification of flow:

(a) to assess valvular disease – stenosis and incompetence

(b) to assess shunts – ASD/VSD/PDA/PAPVR

Contraindications

1. Non-MRI-compatible pacemaker

2. Other active implant/device

3. Claustrophobia.

Relative contraindications

1. Asthma is a relative contraindication in adenosine stress perfusion imaging.

2. Frequent ectopics, bigeminy or rhythms such as AF with fast ventricular response may render functional imaging non-diagnostic.

Patient preparation

1. Standard MRI safety screening

2. Placement of MRI-compatible ECG electrodes for gating of sequences

3. IV cannulation

4. Patients for adenosine stress imaging must avoid caffeine.

Technique

Technique will be varied depending on indication, but will consist of elements from the following.

Localizer images

fGRE or SSFP.

Thoracic overview, cardiac morphology

HASTE black blood imaging.

Functional imaging

Long-axis and short-axis SSFP multi-phase retrospectively gated imaging in the standard cardiac planes viz. echocardiography (Flash/fGRE may be used at high field strengths) 6–8 mm with 2–4 mm gap (spatial resolution ~1.5 × 1.5 × 8 mm, temporal resolution <50 ms). Post processing of these images produces quantification of chamber volumes, myocardial mass and ventricular ejection fraction.

In patients with arrhythmia or an inability to breath-hold lower-resolution untriggered real-time functional imaging can be helpful. Typically temporal resolution is ~40 ms, spatial resolution 2–3 mm.

Tissue characterization

1. T2tse or STIR imaging of oedema for myocarditis and peri-infarct ‘region at risk’

2. T2* mapping for iron load in haemochromatosis

3. T1tse imaging for fatty infiltration (esp ARVC), pericardial anatomy and accurate two-dimensional analysis of the endovasculature.

Myocardial perfusion

Apical, mid and basal Flash/fGRE images every heartbeat during rapid administration of i.v. gadolinium:

(a) during infusion of a vasodilator such as adenosine

(b) at rest.

Dobutamine stress imaging

Functional imaging of ischaemic wall motion abnormalities produced by increasing doses of infused dobutamine.

Early gadolinium enhancement

IRfGRE images immediately following administration of gadolinium chelate to detect/exclude intracardiac thrombus or microvascular obstruction.

Late gadolinium enhancement

Phase sensitive IRfGRE images 10–20 min following administration of gadolinium in the standard cardiac planes. Patterns of enhancement/hyperenhancement are characteristic for myocardial infarction, and for mid-wall fibrosis and infiltration in various cardiomyopathies.

Flow quantification

Phase contrast imaging with velocity encoding ~120% of expected velocity:

1. For assessment of transvalvular velocities and flow volumes in valve disease

2. For derivation of Qp : Qs ratio in intracardiac shunts

3. For demonstration of shunts, including septal defects and conduits.

MR angiography

3D-T1SSFP volumes for coronaries using navigator respiratory gating, or 2D breathhold SSFP.

Contrast-enhanced angiography using isovolumetric 3DT1fGRE sequences for demonstration of aorta, pulmonary artery or pulmonary veins.

Indications

Gated blood-pool study ¹

1. 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.

(Previous indications of first pass radionuclide angiography – for evaluation of right ventricular ejection fraction (RVEF) and detection and quantification of intracardiac shunts are now superseded by echocardiography and MR unless for very specialist indications and will not be described here.)

Contraindications

Significant arrhythmias may make gated blood-pool imaging impossible.

Radiopharmaceuticals

^99mTechnetium-in-vivo-labelled red blood cells, 800 MBq max (8 mSv ED).

Before radiolabelling with ^99mTechnetium (^99mTc)-pertechnetate, the red blood cells are ‘primed’ with an injection of stannous pyrophosphate. The stannous ions reduce the pertechnetate and allow it to bind to the pyrophosphate which adsorbs on to the red blood cells.

Equipment

1. Gamma-camera: equipped with low-energy general purpose collimator

2. Imaging computer: list-mode or multigated acquisition (MUGA)

3. ECG monitor with gating pulse output.

Patient preparation

1. An i.v. injection of ‘cold’ stannous pyrophosphate (20 µg kg^–1) is given directly into a vein 20–30 min before the pertechnetate injection. (Avoid injection via long plastic Teflon-coated cannula which may result in a poor label.)

2. Three ECG electrodes are placed in standard positions to give a gating signal.

Technique

1. Patient supine

2. The ECG trigger signal is connected

3. I.v. injection of ^99mTc pertechnetate

4. One minute is allowed for the bolus to equilibrate before computer acquisition is commenced (see ‘Images’ below).

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. In this, the start of an acquisition cycle is usually triggered by the R wave of the patient’s ECG. A series of 16–32 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 until 100–200 kilo-counts per frame have been acquired in about 10 min. Some degree of arrhythmia can be tolerated using the technique of ‘buffered bad beat rejection’, where cardiac cycles of irregular length are rejected and the data not included in the images. The length of time to acquire an image set increases as the proportion of rejected beats rises.

Images

A number of views may be recorded, depending on the clinical problem:

1. LAO 35–45° with a 15–30° caudal tilt, chosen to give best separation between left and right ventricles. Patient supine. This view is sufficient if only LVEF is required

2. Anterior, patient supine

3. LPO, chosen to give best separation between atria and ventricles. Patient in right lateral decubitus position.

Analysis

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.

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.² Under continuous monitoring, the dose is incrementally increased from 5 to 20 µg kg^–1 min^–1, infusing each dose for 3 min. The infusion is stopped when S-T segment depression of >3 mm, any ventricular arrhythmia, systolic blood pressure >220 mmHg, attainment of maximum heart rate, or any side effects occur.

2. Gated single photon emission computed tomography (SPECT) blood pool acquisition can be used for measurement of left as well as the right ventricular function using special software (Autoquant+) which calculates the left and right ventricular volumes.

3. With gated SPECT using the myocardial perfusion imaging agents ^99mTc-MIBI and ^99mTc-tetrofosmin (see ‘Radionuclide myocardial perfusion imaging’), it is possible to combine ventriculography and perfusion scans in a single study.3,4

When acquiring gated SPECT studies ventricular parameters are usually measured during rest study only because of the length of the examination (20 min).

Aftercare

1. Monitor recovery from exercise

2. Normal radiation safety precautions (see Chapter 1).

Complications

Complications are related to the exercise test and include induction of angina, cardiac arrhythmias and cardiac arrest.

References

1. Metcalfe, MJ. Radionuclide ventriculography. In: Sharp PF, Gemmell HG, Murray AD, eds. Practical Nuclear Medicine. London: Springer, 2005.

2. Konishi, T, Koyama, T, Aoki, T, et al. Radionuclide assessment of left ventricular function during dobutamine infusion in patients with coronary artery disease: comparison with ergometer exercise. Clin Cardiol. 1990; 13:183–188.

3. Fukuoka, S, Maeno, M, Nakagawa, S, et al. Feasibility of myocardial dual-isotope perfusion imaging combined with gated single photon emission tomography for assessing coronary artery disease. Nucl Med Commun. 2002; 23(1):19–29.

4. Anagnostopoulos, C, Underwood, SR. Simultaneous assessment of myocardial perfusion and function: how and when? Eur J Nucl Med. 1998; 25:555–558.

Radionuclide myocardial perfusion imaging

Indications

1. 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

2. Frequent ventricular arrhythmias at rest

3. Contraindications to pharmacological stress agent

4. Second-degree heart block

5. Severe valvular disease, especially aortic valve stenosis.

Radiopharmaceuticals 1,2

1. ^99mTc-methoxyisobutylisonitrile (MIBI or sestamibi), up to 800 MBq (8 mSv ED) for planar imaging, 800 MBq (8 mSv ED) for SPECT (or 1600 MBq max. for the total of two injections in single day rest/exercise protocols). 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. Separate injections are required for stress/rest studies, but image timing is flexible due to minimal redistribution.

2. ^99mTc-tetrofosmin (Myoview) (activity and radiation dose as for MIBI). Similar uptake characteristics and diagnostic efficacy to MIBI, but with easier preparation.

3. ²⁰¹Tl-thallous chloride, 80 MBq max. (18 mSv ED). Thallium is a potassium analogue with initial rapid myocardial uptake in near proportion to coronary blood flow, and subsequent washout and redistribution. Hence, unlike the ^99mTc agents, same-day stress/rest redistribution studies can be performed with a single injection. With principal photon energies of 68–72 and 167 keV and T_1/2 of 73 h, it is not ideal for imaging and gives a higher radiation dose than the newer ^99mTc alternatives. It is increasingly being replaced by ^99mTc agents. However, many still consider ²⁰¹Tl for assessment of myocardial viability and hibernation, with either re-injection at rest or a separate day rest-redistribution study giving the greatest sensitivity.

4. ¹⁸FDG + blood flow PET. The radio-isotope gold standard for viability assessment, but not widely available.³

5. Rubidium-82 PET. This study can be used to assess myocardial perfusion. Not widely available.

Equipment

1. SPECT-capable gamma-camera, preferably dual-headed

2. Low-energy, high-resolution, general purpose or specialized cardiac collimators

3. Pharmacological stressing agent (adenosine or dobutamine [dipyridamole now rarely used]) 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. Lidocaine to reverse serious arrhythmias caused by dobutamine infusion.

Patient preparation

1. Nil by mouth or light breakfast 4–6 h prior to test

2. Cessation of cardiac medication on the day of the test if possible. ß-blockers can be continued and adenosine stress used. Avoid caffeine for 24 h if using dipyridamole or adenosine.

Technique

The principle 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.⁴

Stress regimen

Pharmacological stress has become increasingly widely used instead of physical exercise.⁵ The optimal stress technique aims to maximize coronary arterial flow. The preferred pharmacological stressing agent is adenosine infusion (0.14 mg kg^–1 min^–1 for 6 min).⁶ Adenosine is a potent coronary vasodilator. 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 8–10 s, so most side effects are reversed simply by discontinuing infusion. Stressing with adenosine has now almost completely replaced dipyridamole and will not be discussed here.

There are circumstances where adenosine is contraindicated, e.g. asthma, second-degree heart block or systolic blood pressure <100 mmHg. Dobutamine stress may be employed in these circumstances.⁷ Dobutamine acts as a ß₁ receptor agonist, increasing contractility and heart rate. Under continuous monitoring, the dose is incrementally increased from 5 to 20 µg kg^–1 min^–1, infusing each dose for 3 min. The infusion is terminated when S-T segment depression of >3 mm, any ventricular arrhythmia, systolic blood pressure >220 mmHg, attainment of maximum heart rate, or any side effects occur. Dobutamine is contraindicated in patients with aortic aneurysm. New, more specific targeted agents such as regadenoson (A_2A adenosine receptor agonist) are being developed which could be used in asthmatic patients rather than dobutamine.⁸

^99mTc-MIBI or tetrofosmin rest/stress test

Because MIBI and tetrofosmin have minimal redistribution, separate injections are needed for stress and rest studies. Two-day protocols are optimal, but it is often more convenient to perform both studies on the same day. A number of groups have shown that this is possible without significantly degrading the results, most effectively when the resting study is performed first.⁹

2-Day protocol (stress/rest)

1. Initiate pharmacological stress or exercise

2. Up to 800 MBq MIBI or tetrofosmin is administered i.v. at maximal stress, continuing the stress protocol for 2 min post injection to allow uptake in the myocardium

3. 10–30 min post injection, a milky drink or similar is given to promote biliary clearance; high fluid intake will dilute bowel contents

4. Images are acquired 15–30 min after tetrofosmin or 60–120 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 scan ¹⁰

6. Preferably 2–7 days later, the patient returns for a resting scan

7. Glyceryl trinitrate (GTN) (two 0.3 mg tablets) or equivalent sublingual spray may be given to improve blood flow to ischaemic, but viable segments ¹¹

8. Immediately, up to 800 MBq MIBI or tetrofosmin i.v., is administered and proceed as for stress imaging.

1-Day protocol (stress/rest)

1. Initiate pharmacological stress or exercise; up to 400 MBq MIBI or tetrofosmin i.v. is administered at maximum stress

2. 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 1200 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.

²⁰¹Tl stress/rest test

Since ²⁰¹Tl redistributes after injection, stress/rest studies can be performed with a single injection. However, stress image timing is more critical:

1. Initiate pharmacological stress or exercise

2. Administer 80 MBq ²⁰¹Tl i.v. at maximal stress, continuing the stress protocol for 1 min post injection to allow uptake in the myocardium

3. Image immediately (<5 min)

4. Image at rest 3–4 h after redistribution period, during which time patients should not eat

5. If fixed defects are present in exercise and rest images and assessment of viability and hibernation is required, either:

(a) administer a second smaller dose of 40 MBq ²⁰¹Tl, giving GTN pre injection, and image 20–30 min later. If defects still persist, image again at 18–24 h

(b) perform a separate day rest-redistribution study with 80 MBq ²⁰¹Tl after GTN, and image at 20–30 min and 3–4 h.

Images

SPECT

1. Position patient as comfortably as possible with their arms above their head (or at least the left arm) if possible. SPECT images may be severely degraded by patient movement, so attention should be paid to keeping the patient very still.

2. For the ^99mTc agents, check for activity in bowel loops close to the inferior wall of the heart. This can cause artifacts in the reconstructed images, so if significant activity is seen, delay the imaging to give greater time for clearance.

3. 180° orbit from RAO 45° to LPO 45°, elliptical if possible. With modern dual-headed systems, this can be achieved with the heads at 90° to each other to minimize the amount of camera rotation required.

4. Matrix size and zoom to give a pixel size of 6 mm.

5. 60 projections, with a total imaging time of about 30–40 min for single and 15–25 min for dual-head systems.

6. View the projections as a cine before the patient leaves the department. If available, perform software motion correction. If there is significant movement that cannot be corrected, repeat imaging. Beware ‘diaphragmatic creep’, particularly on ²⁰¹Tl patients breathless after exercise, where the average position of the diaphragm changes as they recover.

Analysis

1. Short, vertical long and horizontal long axis views are reconstructed, taking care to use the same orientation for stress and rest image data sets (modern systems have automatic alignment software).

2. Two-dimensional circumferential profile or ‘bull’s-eye’ polar maps may be generated.

Additional techniques

1. Gated SPECT is now recommended,¹² and with special software (e.g. Cedars Sinai QGS package, Emory cardiac tool box) can provide additional information on ventricular wall motion, ejection fraction and chamber volume. It can also improve specificity by reducing artifactual defects caused by regional myocardial motion and wall thickening.

2. Bull’s-eye maps can be compared to normal databases and displayed quantitatively in terms of severity and extent of relative underperfusion.¹³

3. Attenuation and scatter correction using scanning transmission line sources or CT are now available on most modern dual-headed systems. This technique can improve diagnostic specificity by correcting attenuation artifacts and thereby increasing the normalcy rate. However, algorithms are still being improved, so at present it is wise to view the attenuation-corrected and uncorrected images together to identify possible introduced artifacts.¹⁴

4. The combination of rest ²⁰¹Tl and exercise ^99mTc MIBI or tetrofosmin can be used to assess both ischaemia and viability.¹⁵