Cardiac Tagging/SPAMMWhat is SPAMM?
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SPAMM (SPAtial Modulation of Magnetization) is a technique where RF-saturation pulses are used to place stripes or grids on the heart to follow its motion during the cardiac cycle. The images obtained are typically displayed in a cine format, allowing for both visual and quantitative assessments of wall motion.
In current practice SPAMM is used for clinical applications where information is needed about myocardial contractility. Such situations occur in the setting of focal myocardial ischemia or infiltrative disorders that produce regional wall motion abnormalities not reflected in global quantitative measurements such as ejection fraction or end diastolic volume. |
SPAMM technique, short-axis view
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Three sets of short-axis images (basal, mid-ventricular, and apical) are typically acquired, plus a long-axis, 4-chamber view. A rectangular grid pattern is used for the short-axis views, while a simple stripe pattern is often preferred for long-axis images. The data is then transferred to a separate workstation for advanced post-processing. Semi-automated software is available for calculating parameters such as peak strain timing, circumferential and radial strain components, and twist angle. Such measurements are routinely performed only at the most sophisticated cardiac MR centers, however. More commonly, only a visual assessment of cardiac wall motion based on perceived motion of tags is conducted.
SPAMM technique for producing parallel saturationband across an image.
The simplest form of SPAMM producing a series of parallel stripes is illustrated in the diagram left. Here we have applied two rectangular (hard, non-slice-selective) 45°-pulses followed by an image acquisition sequence. The imaging sequence is arbitrary, but is usually a 2D cardiac-gated SSFP or similar bright blood technique. Sandwiched between the RF-pulses is tagging gradient followed by a large spoiler gradient.
The diagram below illustrates how the tagging process operates. Let us assume that before the SPAMM sequence is initiated, the magnetization (M) of the myocardium is in steady-state equilibrium and directed along the z-axis. The first 45°-tagging pulse rotates M in the yz-plane. Application of the tagging gradient disperses these spins in the transverse (xy) plane, modulating their phases as a function of position similar to that which occurs during application of a conventional imaging gradient. The tagging gradient is of sufficient size to cause the spin phases to wrap many times around 360°. (These phase cycles will be transformed into z-axis modulation and SPAMM stripes during the next two steps.)
The diagram below illustrates how the tagging process operates. Let us assume that before the SPAMM sequence is initiated, the magnetization (M) of the myocardium is in steady-state equilibrium and directed along the z-axis. The first 45°-tagging pulse rotates M in the yz-plane. Application of the tagging gradient disperses these spins in the transverse (xy) plane, modulating their phases as a function of position similar to that which occurs during application of a conventional imaging gradient. The tagging gradient is of sufficient size to cause the spin phases to wrap many times around 360°. (These phase cycles will be transformed into z-axis modulation and SPAMM stripes during the next two steps.)
Spin evolution in the SPAMM technique
The second RF-pulse tips the entire ensemble of dephased spins by another 45°. These doubly rotated spins now lie along an obliquely oriented cone with both longitudinal and transverse components. In the final step the transverse components of these spins will be destroyed by endogenous T2 decay and the large spoiler gradient. This leaves only residual longitudinal (z-) magnetization components whose magnitudes vary in a sinusoidal pattern reflecting the original transverse phase dispersion. When the imaging module is performed, these spatial variations in magnetization will be translated into bands of oscillating signal intensity across the image.
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The SPAMM sequence pictured above produces a single set of stripes parallel to the tagged gradient axis. To create a grid, a second set of RF-pulses and gradients must be applied in an orthogonal direction.
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SPAMM grid requires 2 sets of pulses & gradients
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The width and spacing of bands depends in a complicated manner on the area under the tagging gradient as well as the flip angles of the RF-pulses. In common practice, the RF-pulses used for SPAMM are not simple 45°-pulses but a series of closely-spaced composite pulses of the binomial type (see related Q&A).
Fading of SPAMM tags late in cardiac cycle
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Because of T1-recovery SPAMM tags tend to fade late in the cardiac cycle. By end-systole, tag lines may merge or become indistinct as shown in the figure. This phenomenon may be minimized by using a low flip angle (~10°) for the SSFP imaging portion. Improved persistence of tag lines may also be obtained by increasing flip angles of the RF-tagging pulses or by using composite (binomial) RF-pulses.
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References
Axel L, Dougherty L. MR imaging of motion with spatial modulation of magnetization. Radiology 1989; 171:841-845. (Original description of the SPAMM technique).
Fischer SE, McKinnon GC, Maier SE, Boesiger P. Improved myocardial tagging contrast. Magn Reson Med 1993, 30:191-200. (Description of CSPAMM).
Ibrahim E-S H. Myocardial tagging by cardiovascular magnetic resonance: evolution of techniques—pulse sequences, analysis algorithms, and applications. J Cardiovasc Magn Reson 2011; 13:36 (Great review, including advanced techniques such as SENC, HARP, and DENSE)
Mosher TJ, Smith MB: A DANTE tagging sequence for the evaluation of translational sample motion. Magn Reson Med 1990; 15:334-339.
Zerhouni EA, Parish DM, Rogers WJ, et al. Human heart: tagging with MR imaging — a method for noninvasive assessment of myocardial motion. Radiology 1988; 169:59-63. (First implementation of RF-tagging to study myocardial motion).
Axel L, Dougherty L. MR imaging of motion with spatial modulation of magnetization. Radiology 1989; 171:841-845. (Original description of the SPAMM technique).
Fischer SE, McKinnon GC, Maier SE, Boesiger P. Improved myocardial tagging contrast. Magn Reson Med 1993, 30:191-200. (Description of CSPAMM).
Ibrahim E-S H. Myocardial tagging by cardiovascular magnetic resonance: evolution of techniques—pulse sequences, analysis algorithms, and applications. J Cardiovasc Magn Reson 2011; 13:36 (Great review, including advanced techniques such as SENC, HARP, and DENSE)
Mosher TJ, Smith MB: A DANTE tagging sequence for the evaluation of translational sample motion. Magn Reson Med 1990; 15:334-339.
Zerhouni EA, Parish DM, Rogers WJ, et al. Human heart: tagging with MR imaging — a method for noninvasive assessment of myocardial motion. Radiology 1988; 169:59-63. (First implementation of RF-tagging to study myocardial motion).
Related Questions
How do they make those movies of the beating heart?
How do they make those movies of the beating heart?