Standardized cardiovascular magnetic resonance (CMR) protocols 2013 update

This document is an update to the 2008 publication of the Society for Cardiovascular Magnetic Resonance (SCMR) Board of Trustees Task Force on Standardized Protocols. Since the time of the original publication, 3 additional task forces (Reporting, Post-Processing, and Congenital Heart Disease) have published documents that should be referred to in conjunction with the present document. The section on general principles and techniques has been expanded as more of the techniques common to CMR have been standardized. There is still a great deal of development in the area of tissue characterization/mapping, so these protocols have been in general left as optional. The authors hope that this document continues to standardize and simplify the patient-based approach to clinical CMR. It will be updated at regular intervals as the field of CMR advances.


Introduction
This document is an update to the 2008 publication of the Society for Cardiovascular Magnetic Resonance (SCMR) Board of Trustees Task Force on Standardized Protocols [1]. Since the time of the original publication, 3 additional task forces have published documents that should be referred to in conjunction with the present document. The first is the document on Reporting published by that SCMR Task Force in 2010 [2]. All references to reporting of the findings from the protocols listed have been removed from the present document as they are covered in the aforementioned document. In addition, all references to analysis methodologies have been removed from the current protocols document as they are covered in their entirety in the recent publication of the SCMR Task Force on Post-Processing [3]. All protocols relative to congenital heart disease have been removed, as a separate document has been recently published in regards to this topic [4].
The section on general principles and techniques has been expanded as more of the techniques common to CMR have been standardized. There is still a great deal of development in the area of tissue characterization/ mapping, so these protocols have been in general left as optional. The authors hope that this document continues to standardize and simplify the patient-based approach to clinical CMR. It will be updated at regular intervals as the field of CMR advances.

General Techniques
Field Strength Considerations 1. CMR can be performed at different field strength.
1.5T systems are currently used for the majority of examinations. 2. CMR at 3T requires careful shimming and adjustment of the radiofrequency pulses to avoid artifacts. 3. As a result of improved signal-to-noise ratio (SNR), 3T is advantageous for first pass contrast-enhanced perfusion imaging. Furthermore tagging sequences and 4D flow techniques may benefit from 3T. 4. Steady-state free precession sequences, often the choice for cine imaging at 1.5T, have several challenges at 3T including increased dark banding artifacts, flow artifacts, and suboptimal flip angle choices because of specific absorption rate (SAR) restrictions. 5. Devices that have been tested at 1.5 T may not be safe at 3T: check specific information relating to MRI safety of devices at higher magnetic field strength. 2nd or 3rd degree atrioventricular (AV) block or sinus node dysfunction Systolic blood pressure less than 90 mm Hg Sinus bradycardia (heart rate<40 bpm) Active bronchoconstrictive or bronchospastic disease with regular use of inhalors Known hypersensitivity to adenosine or regadenoson (Side effects are described as less significant with regadenoson than with adenosine, however, the half life of regadenoson is longer)

Patient preparation
1. Obtain informed consent for the stress test 2. To fully exert its effects patients should optimally refrain from the following medications for 12-24 hours prior to the examination due to potential of counteraction against stress agent.
Dobutamine: ß-blockers and nitrates. Adenosine/regadenoson: caffeine (coffee, tea, caffeinated beverages or foods e.g. chocolate, caffeinated medications), theophylline, dipyridamole Note: There is increasing data that the effects of caffeine and nicotine can be overcome by higher doses of adenosine as well as regadenoson.
1. Fasting is not mandatory, but is often advised because recognized adverse effects of stress drugs include nausea and vomiting, which may be problematic when lying supine in the restricted space of the magnet 2. Two intravenous lines should be available, one for gadolinium and one for adenosine, one in each arm. Preferential site of contrast infusion is antecubital. Blood pressure cuff should be used with care taken not to interfere with gadolinium or adenosine infusion. For regadenoson only one line is required. 1. Volumes and injection rates depend on scan duration: the given values are recommendations for typical scan times. 2. Injection rates are different for 1 molar contrast agents. As a general rule, divide the given injection rates by a factor of 2. 3. Contrast agents with higher relaxivity (e.g., gadobenate dimeglumine) require smaller doses. 4. Throughout the protocols, the term "gadolinium" refers to gadolinium chelates

Potential adverse effects
Safety considerations: 1. The use of gadolinium contrast should be avoided in patients with stage 4 or 5 chronic kidney disease (estimated glomerular filtration rate <30 mL/min/ 1.73 m 2 ), particularly for those on dialysis, as well as patients with acute renal failure and chronic liver disease, due to concerns regarding nephrogenic systemic fibrosis (NSF). 2. The dose of gadolinium contrast used should be as low as possible to achieve adequate image quality. 3. The risk of NSF depends in part upon the gadolinium chelate used. Use institutional, regional, or national guidelines to guide choice of agent in patients with renal dysfunction. 4. If no alternative is available in dialysis patients such that gadolinium must be used, dialysis should be performed as per institutional, regional or national guidelines.
Left ventricular structure and function module 1. Scout imagingtransaxial, coronal, sagittal 2. Transaxial (8-10 mm) set of steady state free precession (SSFP) or fast spin echo images through the chest. 3. Scout to line up short axis imagescine acquisitions are preferable to single shot as long axis motion and inflow should be visualized a. Vertical long axis prescribed orthogonal to transaxial scouts aligned through the apex and center of the mitral valve b. Horizontal long axis aligned orthogonal to the vertical long axis, passing through the apex and center of the mitral valve 4. SSFP is the method of choice for cine imaging because it provides high SNR and excellent contrast between myocardium and blood pool a. At 3T, SSFP cine images may be compromised by artifact and spoiled gradient-echo sequences can be considered as an alternative b. Strategies to reduce or move banding artifact include shimming, reducing the TR, and adjusting the RF frequency (frequency 'scout' sequence can be helpful for this) 5. Steady state free precession short axis cine images, from the mitral valve plane through the apex. The basal most short axis slice should be located immediately on the myocardial side of the atrioventricular junction at end-diastole prescribed from the previously acquired long axis cines. a. Slice thickness 6-8 mm, with 2-4 mm interslice gaps to equal 10 mm. b. Temporal resolution ≤45 ms between phases c. Parallel imaging used as available 6. Steady state free precession long axis cine images a. The 4 chamber long axis is prescribed from the vertical long axis through the apex and center of the mitral and tricuspid valves. This can be cross-checked on basal short axis cines, using the costophrenic angle (margin) of the RV free wall. b. Vertical long axis, prescribed from the scout already acquired c. LV outflow tract (LVOT) long axis, passing through the apex, the center of the mitral valve b. Single-shot imaging (SSFP readout) performed as backup for patients with irregular heart rhythm, and/or difficulty breath holding. 2. Need at least 10 minute wait after gadolinium injection (for gadolinium-chelate dosing see Table 1). Note -The delay may be shorter than 10 minutes if lower doses are used as blood pool signal falls below that of late enhanced myocardium. Images are to be acquired during diastolic stand-still. 3. Same views as for cine imaging (short-and longaxis views) 4. Slice thickness, same as for cine imaging 5. In-plane resolution,~1.4-1.8 mm 6. Acquisition duration per R-R interval below 200 ms, but should be less in the setting of tachycardia to avoid image blurring. 7. Inversion time set to null normal myocardium.
Alternatively, a PSIR sequence can be used, requiring less frequent adjustment of the TI. 8. Read-out is usually every other heart beat, but should be modified to every heart beat in the setting of bradycardia, and every third heart beat in the setting of tachycardia or arrhythmia.
Adenosine/Regadenoson stress perfusion CMR 1. LV structure and function module (alternatively this can be performed between stress and rest perfusion, although performance immediately after gadolinium infusion may reduce the contrast of the blood-endocardium interface) 2. Adenosine stress perfusion imaging (at least 3 minute infusion of 140 ug/kg body weight/min, optional up to 210 ug/kg body weight/min).
Optioninitial adenosine infusion may be performed with the patient outside the bore of the magnet. a. First pass perfusion module b. During last minute of adenosine, gadolinium is injected c. After imaging for 40-50 heart beats by which time gadolinium has passed through the LV myocardium, adenosine is stopped. d. Continuous ECG monitoring and BP measured at baseline, during infusion, and for at least 2 minutes post-infusion of adenosine. 3. Alternatively: Regadenoson stress perfusion imaging (bolus injection of 0.4 mg). a. First pass perfusion module b. Approximately 2 minutes after regadenoson injection, inject gadolinium c. Image for 40-50 heart beats by which time gadolinium has passed through the LV myocardium d. Continuous ECG monitoring and BP measured at baseline and every other minute for at least 6 minutes post injection of regadenoson. 4. Rest Perfusion a. Need at least 10 minute wait for gadolinium to wash out from stress perfusion imaging. During this period stress images can be reviewed, cine imaging can be completed (e.g. long-axis views), valvular evaluation can be performed, etc. b. Perfusion imaging repeated without adenosine/ regadenoson using same dose of gadolinium (Note: flow may not have returned to baseline at 10 minutes after regadenoson) c. If stress images are normal and free of artifacts, rest perfusion can be eliminated. Additional gadolinium may be given as needed for late gadolinium enhancement (for a total of 0.1 -0.2 mmol/kg) 5. Late Gadolinium Enhancement module a. Need to wait at least 5 minutes after rest perfusion if performed 6. Optional -Full quantification a. Consider using a dual bolus approach to eliminate effect of nonlinearity between contrast agent concentration and signal intensity. This requires injection of a diluted pre-bolus in a standardized fashion. b. Consider using a dual contrast sequence.
Similarly to the dual bolus approach this corrects for non-linearity of signal intensity and contrast agent concentration without additional contrast dilution and injection but requires specific scanner software that may not be available on all scanners c. Consider adding proton density images before the contrast injection. This can be used as baseline correction for full quantification but requires specific scanner software that may not be available on all scanners. Sequence: one-direction ("through-plane") motionencoded cine gradient echo sequences are typically applied 3. For optimal results, the imaging plane should be a) centered in the vessel of interest b) aligned orthogonally to the expected main blood flow direction in two spatial directions c) centered in the iso-center of the magnet 4. Imaging parameters: slice thickness 5-8 mm; in-plane resolution at least 1/10th of the vessel diameter. Velocity encoding sensitivity (V enc ) has to be adapted to the expected velocitiesafter each scan, phase difference images have to be checked for aliasing. If aliasing is present, V enc settings need to be adapted accordingly. If available, a velocity scout may allow optimal setting of the V enc . 5. Acquired time frames on the order of 20-30 suffice for clinical routine. For read-out, k-space segmentation over multiple heart beats can be used within limits of breath holding capabilities. Navigator-based non-breathhold techniques can be applied to improve the temporal or spatial resolution if necessary. 6. Echo time (TE) should be set to minimal, particularly when stenoses are imaged

Advanced Tissue Characterization Module
The area of tissue characterization is a rapidly developing field and the pulse sequences available on different vendor platforms vary significantly. Thus, the modules listed below are general guidelines only as there is no standardization yet in this arena. Normal values should be developed at individual or partner institutions using similar platforms and pulse sequences. 1. Performed to assess cardiac iron deposition in disease entities such as thalassemia major. Images typically acquired in concert with LV function imaging. If T2* images are acquired as part of a contrast-enhanced evaluation for cardiomyopathy, the T2* images should be obtained prior to contrast administration. 2. The pulse sequence is a single breathhold, gradientecho, multi-echo scan with a series of 6-9 echo times beginning at~2 ms and extending to~18 ms, with each echo iteratively spaced by~2 ms. A delay time of 0 ms after the R wave typically is used.
Optional -In patients with severe iron deposition a pulse sequence with shorter echo spacing could be helpful to accurately determine T2* values: a series of 6-9 echo times beginning at~1 ms and extending to~12 ms, with each echo iteratively spaced by~1 ms. 3. A single mid-ventricular short-axis image is acquired. 4. Slice thickness of 8-10 mm; In-plane resolution, 1.6-3.0 mm 5. (Optional) An imaging sequence similar to the above, though non-ECG-gated, is acquired in the axial orientation through the mid portion of the liver to evaluate hepatic iron deposition. The absence of ECG-gating will allow for closer spacing of iteratively advanced echo times, and therefore a greater number of echoes will be acquired.
Disease specific protocols -Ischemic heart disease Acute MI or acute coronary syndromes Valve morphology assessment with SSFP cine in the plane of the valve in question. Care must be taken to optimize the level and angle of imaging b. Noteif planimetry of a stenotic valve is to be attempted, a contiguous or slightly overlapping stack of high resolution cines transecting the line of the jet and moving from orifice level to immediately downstream is recommended. Planimetry is most likely to be valid where the cross section of the orifice, or rather of the jet, is clearly delineated. This may not always be the case due to fragmented or oblique jet flow. c. Gradient echo or hybrid gradient echo/echo planar imaging may visualize regurgitant jets with a higher sensitivity (for qualitative purposes only). d. In mitral or tricuspid regurgitation, a contiguous stack of 5 mm cines is recommended aligned with the direction of inflow and transecting the principal line of coaptation, moving from the more superior commissure to the inferior. The orientation can be that of the LVOT plane for the mitral and transaxial for the tricuspid. Such a stack enables assessment of tethering, prolapse, or regurgitation through the scallops of both mitral leafletes. e. Adapt velocity encoding to actual velocity (using lowest velocity without aliasing). f. Use lowest TE possible for high velocity jet flows.

Pericardial disease
1. LV structure and function module 2. T1 or T2-weighted fast spin echo images a. 2-3 representative long axis images and 3-4 representative short axis images to measure pericardial thickness (normal ≤3 mm) b. If pericardial cyst is suspected, refer to masses protocol 3. Optional -If regions of thickened pericardium noted -T1-weighted gradient echo myocardial tagged cine sequences to demonstrate presence or absence of epicardial/pericardial slippage (2-3 long axis images and 1-2 short axis images) 4. Real-time imaging during dynamic breathing maneuvers is valuable for evaluation of ventricular interdependence a. Mid-ventricular short-axis plane is preferred b. Cine imaging temporal resolution is preferably below 60 ms c. Patients are instructed to breathe deeply in and out and the total imaging period should be at least 2 complete respiratory cycles d. Abnormal septal motion (early diastolic septal flattening or inversion) during onset of inspiration is consistent with a constrictive physiology 5. Late Gadolinium Enhancement module a. Acquisition with and without fat saturation is helpful to distinguish pericardial inflammation from epicardial or pericardial fat Cardiac and paracardiac masses, including thrombi