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MR Imaging Abbreviations, Definitions, and Descriptions: A Review¹

¹ From the Department of Radiology, University of North Carolina Hospitals and School of Medicine, 101 Manning Dr, Chapel Hill, NC 27599-7510 (M.A.B., R.C.S.), and the Siemens Training and Development Center, Cary, NC (M.A.B.). Received September 2, 1998; revision requested October 19; final revision received February 26, 1999; accepted April 5. Address reprint requests to R.C.S. (e-mail: richsem@med.unc.edu).

View larger version (8K): [in a new window]   Figure 1. A 2D pulse sequence timing diagram. Fixed amplitude pulses are indicated as simple deviations from horizontal. Variable amplitude pulses are indicated as hatched regions. Section (slice) selection and signal detection are repeated in amplitude, duration, and relative timing each time the sequence is executed. A single phase-encoding table is present, which is incremented in amplitude each time the sequence is executed.

View larger version (8K): [in a new window]   Figure 2. A 3D pulse sequence timing diagram. Volume excitation and signal detection are repeated in amplitude, duration, and relative timing each time. Two phase-encoding tables are present, one in the phase-encoding direction and one in the section (slice) direction, which are independently incremented in amplitude each time the sequence is executed. The compensation gradient in the section direction is incorporated into the gradient table.

View larger version (9K): [in a new window]   Figure 3. Single-echo spin-echo pulse sequence timing diagram. A pair of RF pulses produces a single echo. This echo is always detected in the presence of a readout gradient of constant amplitude. The excitation-detection process is repeated many times, each time with a different amplitude of the phase-encoding gradient applied prior to signal detection. ADC = analog-to-digital conversion.

View larger version (94K): [in a new window]   Figure 4. Transverse T1-weighted spin-echo image (500/15 [TR msec/TE msec]) shows that the cerebrospinal fluid in the lateral ventricles has low signal intensity (arrow).

View larger version (8K): [in a new window]   Figure 5. Multiple-echo spin-echo pulse sequence timing diagram, two echoes illustrated. Multiple refocusing RF pulses are used to produce multiple echoes. Each echo is detected in the presence of a constant amplitude readout gradient, following a common amplitude of the variable phase-encoding gradient. ADC = analog-to-digital conversion.

View larger version (95K): [in a new window]   Figure 6. Transverse T2-weighted spin-echo image (2,000/90) shows that the cerebrospinal fluid in the lateral ventricles has high signal intensity (arrow).

View larger version (15K): [in a new window]   Figure 7. Echo train spin-echo pulse sequence timing diagram. Illustrated is an echo train length of three. Multiple refocusing RF pulses are used to produce multiple echoes. Each echo is detected in the presence of a constant amplitude readout gradient, following a unique amplitude of the variable phase-encoding gradient. Arrows indicate the stepping direction of the phase-encoding tables. ADC = analog-to-digital conversion.

View larger version (10K): [in a new window]   Figure 8. Inversion-recovery pulse sequence timing diagram. A 180° inversion pulse is applied prior to a 90° excitation pulse of a spin-echo acquisition. ADC = analog-to-digital conversion.

View larger version (10K): [in a new window]   Figure 9. T1 recovery curves following 180° inversion pulse. a, Tissue with a short T1 value (dashed arrow) and that with a long T1 value (solid arrow) have negative longitudinal magnetization and are assigned different pixel values. b, Tissue with a short T1 value (dashed arrow) has positive longitudinal magnetization, and tissue with a long T1 value (solid arrow) has negative longitudinal magnetization. Phase sensitive image reconstruction assigns different pixel values. Magnitude image reconstruction assigns equal pixel values. c, Tissue with a short T1 value (dashed arrow) has positive longitudinal magnetization, and tissue with a long T1 value has zero longitudinal magnetization and contributes no signal intensity to the image.

View larger version (139K): [in a new window]   Figure 10. Sagittal echo train inversion-recovery, STIR image (5,000/30/150 [TR msec/TE msec/TI msec]) shows that fat has low signal intensity, such as that for bone marrow, and fluid has high signal intensity, such as that for suprapatellar effusion (arrow).

View larger version (9K): [in a new window]   Figure 11. Gradient-echo pulse sequence timing diagram. This class of sequences is characterized by the absence of a 180° refocusing pulse. Echo formation is accomplished by application of gradient pulses of opposite polarity (readout direction). ADC = analog-to-digital conversion.

View larger version (126K): [in a new window]   Figure 12a. Transverse (a) in-phase (140/4.5, 80° flip angle) and (b) out-of-phase (140/2.25, 80° flip angle) spoiled gradient-echo images. Increased fat content in adrenal gland (arrow) due to adrenal adenoma causes a reduction of signal intensity in b compared to that in a.

View larger version (143K): [in a new window]   Figure 12b. Transverse (a) in-phase (140/4.5, 80° flip angle) and (b) out-of-phase (140/2.25, 80° flip angle) spoiled gradient-echo images. Increased fat content in adrenal gland (arrow) due to adrenal adenoma causes a reduction of signal intensity in b compared to that in a.

View larger version (133K): [in a new window]   Figure 13. Transverse spoiled gradient-echo image (130/4, 80° flip angle) acquired following administration of a T1 relaxation contrast agent shows metastatic liver lesions (arrows) from colon cancer.

View larger version (8K): [in a new window]   Figure 14. A series of equally spaced RF pulses produces spin echoes that form at the time of subsequent echoes. Once a steady state is reached, signal is produced prior to the excitation pulse, which is echo reformation, and following the excitation pulse, which is a combination of echo and free induction decay. Images can be produced from either the preexcitation signal (S-) or from the postexcitation signal (S+).

View larger version (9K): [in a new window]   Figure 15. Magnetization-prepared gradient-echo pulse sequence timing diagram. Preparation period is to the left of the vertical line and is executed one time. The preparation pulse illustrated is a 180° inversion pulse. Portion of the diagram to the right of the vertical line represents the data collection period and is executed multiple times, depending on the acquisition parameters. ADC = analog-to-digital conversion.

View larger version (19K): [in a new window]   Figure 16. T1 recovery curve for the pulse sequence illustrated in Figure 10. The data collection period corresponds to the right side of Figure 10. At the time during the data collection when the low-amplitude phase-encoding echoes are acquired, tissue a (solid line) contributes no signal, while tissue b (dashed line) contributes considerable signal to the echo. The image will have high signal intensity from tissue b but low signal intensity from tissue a.

View larger version (146K): [in a new window]   Figure 17. Transverse T1-weighted magnetization-prepared image (8/4.3/163, 8° flip angle). One second of imaging produced this image with minimal artifact from respiratory motion and slight artifact (arrow) from blood flow in the aorta.

View larger version (17K): [in a new window]   Figure 18. Hybrid gradient-echo-spin-echo pulse sequence timing diagram. Illustrated is an echo train length of six. Arrows indicate the stepping direction of the gradient tables. ADC = analog-to-digital conversion.

View larger version (11K): [in a new window]   Figure 19. Echo-planar pulse sequence timing diagram, spin-echo type. Illustrated is an echo train length of eight. ADC = analog-to-digital conversion.

View larger version (109K): [in a new window]   Figure 20. Transverse diffusion-weighted echo-planar image (TE = 123 msec; b value = 1,000 sec/mm2) shows an area of increased signal intensity (arrow) in the posterior parietal cortex corresponding to tissue with restricted motion of cellular water, indicative of stroke.

View larger version (6K): [in a new window]   Figure 21. Single-voxel PRESS pulse sequence timing diagram. Note that the analog-to-digital conversion (ADC) sampling begins at the peak of the echo signal.

View larger version (8K): [in a new window]   Figure 22. Chemical shift imaging PRESS pulse sequence timing diagram. The compensation gradient in the Gy direction is incorporated into the gradient table. Note that the analog-to-digital conversion (ADC) sampling begins at the peak of the echo signal.

View larger version (11K): [in a new window]   Figure 23. Water excitation. A 121 (1, 2, 1 at top of image) composite pulse is shown with a total flip angle of 90°. Prior to the first RF pulse (1 at bottom of image), both water (solid arrows) and fat (dashed arrows) hydrogen are unexcited. At the end of the first RF pulse (2 at bottom of image), both are excited 22.5°. Because of the difference in resonant frequencies between fat and water, the fat hydrogen becomes out of phase with the water hydrogen. The time for the second RF pulse (3) is chosen so that the fat hydrogen is exactly 180° out of phase. At the end of the second RF pulse (4), the water proton is rotated 67.5° while the fat hydrogen is rotated -22.5°. A similar delay is chosen between the second and third RF pulses (5). At the end of the third RF pulse (6), the fat hydrogen is at 0° (unexcited), while the water hydrogen is rotated 90°.

View larger version (124K): [in a new window]   Figure 24a. Effect of magnetization transfer pulse. (a) No magnetization transfer pulse, (b) magnetization transfer pulse. (40/7, 25° flip angle, for a and b.) Normal gray matter and white matter are suppressed by application of a magnetization transfer pulse, enabling smaller diameter vessels (arrow) to be seen.

View larger version (133K): [in a new window]   Figure 24b. Effect of magnetization transfer pulse. (a) No magnetization transfer pulse, (b) magnetization transfer pulse. (40/7, 25° flip angle, for a and b.) Normal gray matter and white matter are suppressed by application of a magnetization transfer pulse, enabling smaller diameter vessels (arrow) to be seen.