DOI: 10.1148/radiol.2462061674
(Radiology 2008;246:589-595.)
© RSNA, 2008
N/2 Ghosting Artifacts: Elimination at 3.0-T MR Cholangiography with SPACE Pulse Sequence1
Clare M. Haystead, MD,
Brian M. Dale, PhD, and
Elmar M. Merkle, MD
1 From the Department of Radiology, Duke University Medical Center, Erwin Rd, Durham, NC 27710 (C.M.H., E.M.M.); and Siemens Medical Solutions, Cary, NC (B.M.D.). Received September 27, 2006; revision requested December 7; revision received March 1, 2007; accepted March 21; final version accepted July 16.
Address correspondence to C.M.H. (e-mail: clare.haystead{at}duke.edu).
 |
ABSTRACT
|
|---|
This HIPAA-compliant study had institutional review board approval, with waiver of informed consent. The purpose was to test the hypothesis that, compared with a standard magnetic resonance (MR) cholangiography sequence, MR cholangiography with a sampling perfection with application optimized contrasts using different flip angle evolutions (SPACE) sequence reduces ghosting artifacts while maintaining image quality and sufficient contrast-to-noise ratio (CNR) at 3.0 T. The study population consisted of 15 women and 14 men (mean age, 47.2 years ± 18.1 [standard deviation]) who were consecutively referred for MR cholangiography between November 2004 and November 2005. Acquisition times were lower and N/2 ghosting artifacts were eliminated with SPACE. However, the SPACE sequence yielded images that were visually grainier and had lower CNR. Overall, the readers preferred the appearance of images obtained with the SPACE sequence, most likely because of the elimination of N/2 ghosting artifacts.
© RSNA, 2008
|
INTRODUCTION
|
|---|
Magnetic resonance (MR) cholangiography is an important noninvasive imaging modality for the biliary ductal system. It has replaced endoscopic retrograde cholangiography in situations in which intervention is not anticipated (1). MR cholangiography has become more clinically useful since the recent development of respiratory-triggered three-dimensional (3D) T2-weighted fast spin-echo (SE) techniques. These sequences enable the acquisition of isotropic voxel data sets with a spatial resolution on the order of 2.0 mm3 or smaller. A drawback of the excellent spatial resolution is a requirement for longer imaging times.
Three-tesla MR imaging systems seem well suited for respiratory-triggered fast SE sequences, with their inherent gain in signal-to-noise ratio (SNR) over 1.5-T MR imaging systems (2,3). Acquisition times may be substantially shortened by the implementation of parallel imaging techniques, while excellent spatial resolution and sufficient SNR are maintained. The use of variable flip angles can further decrease the acquisition time while decreasing the specific absorption rate (4).
The purpose of our study was to retrospectively test the hypothesis that MR cholangiography with a sampling perfection with application optimized contrasts using different flip angle evolutions (SPACE) sequence eliminates ghosting artifacts while maintaining image quality and sufficient contrast-to-noise ratio (CNR) at 3.0 T (5).
|
MATERIALS AND METHODS
|
|---|
B.M.D. is an employee of Siemens Medical Solutions (Cary, NC); however, C.M.H. and E.M.M. had control of the data included. Siemens provided the SPACE sequence, in addition to technical support. No financial support was provided by Siemens.
This retrospective study was approved by our institutional review board, with waiver of the need to obtain informed consent. The study was compliant with Health Insurance Portability and Accountability Act guidelines.
The study population consisted of 15 women and 14 men (mean age, 47.2 years ± 18.1 [standard deviation]; range, 19–79 years) who were consecutively referred for MR cholangiography for various clinical indications (choledocholithiasis, pancreatitis, biliary ductal mapping before hepatic surgery) between November 2004 and November 2005. There were 18 outpatients and 11 inpatients (mean body weight, 80 kg ± 21).
MR Imaging Sequence Protocol
MR imaging was performed with a 3.0-T MR system (Magnetom Trio; Siemens Medical Systems, Erlangen, Germany) with an eight-channel torso array coil (USA Instruments, Aurora, Ohio). Our standard MR cholangiography sequence protocol was implemented, with the addition of the SPACE sequence (3). Our study compared the "standard" 3D fast SE T2-weighted sequence and a SPACE sequence. Source images were obtained in the coronal plane.
Respiratory triggering was performed by using the prospective acquisition correction, or PACE, technique with both sequences (6,7). Detailed sequence parameters were as follows: repetition time/echo time msec, one respiratory cycle/645; maximum refocusing flip angle, 180°; number of signals acquired, one; receiver bandwidth, 257 Hz/pixel; and parallel imaging acceleration factor, one for the 3D fast SE T2-weighted sequence and one respiratory cycle/746; maximum refocusing flip angle, 120°; number of signals acquired, two; receiver bandwidth, 751 Hz/pixel; and parallel imaging acceleration factor, three for the SPACE sequence.
The image matrix for each sequence was identical, at 240 x 256. The field of view ranged from 30 to 35 cm2, depending on the patient's size. Thirty-six sections per slab (2-mm noninterpolated section thickness) were acquired for the standard sequence, compared with 56 sections per slab (1.3-mm noninterpolated section thickness) for the SPACE sequence. In both cases, a partial Fourier factor of 75% was used, and the images were interpolated to obtain a total of 72 interpolated sections per slab for each sequence, with an interpolated section thickness of 1 mm. Maximum intensity projections (MIPs) in a coronal orientation were generated from each data set with an MR imaging workstation (Leonardo; Siemens Medical Systems). The source and MIP images were evaluated side by side on the workstation.
The SPACE sequence has three differences from the standard fast SE sequence (5): First, it uses a variable flip angle, which allows a larger number of refocusing pulses to be used per repetition time while good T2-weighted contrast and low specific absorption rate are maintained. The SPACE sequence uses a reconstruction algorithm known as generalized autocalibrating partially parallel acquisition, or GRAPPA, to reduce the number of refocusing pulses required for a given spatial resolution. With this method, time savings are achieved by omitting some of the phase-encoding steps during acquisition and interpolating the missing data from redundant spatial information located within individual elements of the radiofrequency coil array. The final difference is a direct consequence of the previous two. The standard respiratory-triggered fast SE sequence acquires half of the k-space lines per partition in a single respiratory cycle, while the SPACE sequence acquires an entire k-space partition in a single respiratory cycle (Fig 1).
View larger version (17K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 1: Standard respiratory-triggered fast SE T2-weighted sequence versus SPACE. Navigators (Nav.) are used to detect diaphragm position. Two respiratory cycles are required to acquire one k-space partition for the standard 3D fast SE T2-weighted sequence, with the even and odd lines in k-space coming from even and odd respiratory cycles, respectively. In contrast, an entire k-space partition is acquired in a single respiratory cycle with the SPACE sequence.
|
|
Quantitative Data Analysis
Signal amplitudes of the common bile duct and the right and left hepatic ducts were measured for both MR cholangiography sequences on the MIP images by defining oval regions of interest. Regions of interest for the signal intensity of bile were chosen in homogeneous, artifact-free areas of the common bile duct and right and left hepatic ducts. Periductal tissue and hepatic parenchyma were used to measure background signal intensity for the common bile duct and the intrahepatic ducts, respectively. Regions of interest for the signal intensity of the periductal tissue and hepatic parenchyma were chosen in homogeneous and artifact- and noise-free areas adjacent to the common bile duct and within the liver parenchyma, respectively. The noise was measured as the standard deviation of the signal with as large a region of interest as possible in artifact-free areas outside the patient's body. The regions of interest ranged from 20 to 600 mm2. All quantitative measurements were performed in a blinded fashion by a board-certified fellow in abdominal imaging (C.M.H.).
Each signal intensity value was calculated as the mean value in three separately sampled regions of interest. Common bile duct–to–periductal tissue CNRs were calculated between the signal amplitudes in the common bile duct and those in the periductal tissue, divided by the standard deviation of the background noise. Intrahepatic bile duct–to-liver CNRs were calculated in an analogous way. In addition, the acquisition time for each MR cholangiography sequence was recorded.
Qualitative Data Analysis
A board-certified radiologist (E.M.M., with 7 years of experience in abdominal MR imaging [reader 1]) and a board-certified fellow (C.M.H. [reader 2]) independently performed the qualitative readings. Both readers were unblinded to the MR pulse sequence type and independently assessed the image quality of the source images and the MIP images obtained with the 3D fast SE T2-weighted sequence and the SPACE sequence in a side-by-side comparison (ie, the source images obtained with the two sequences were compared, and the MIP images obtained with the two sequences were compared). Reader preference was scored for each patient by using a five-point differential receiver operating characteristic curve (DROC) as follows: A score of 1 indicated strong preference for the fast SE T2-weighted sequence; a score of 2, slight preference for the fast SE T2-weighted sequence; a score of 3, equal preference for both sequences; a score of 4, slight preference for the SPACE sequence; and a score of 5, strong preference for the SPACE sequence.
A more detailed visual assessment of the images was performed by the same two abdominal radiologists independently. This assessment included evaluation of the presence and severity of the following issues: B1 inhomogeneity artifacts, N/2 ghosting artifacts, and overall image noise. B1 inhomogeneity artifacts were defined as a loss of MR signal within the center of the image. N/2 ghosting artifacts were defined as ghost artifacts of fluid-filled structures such as the gallbladder, stomach, or duodenum along the phase-encoding axis (8). N/2 ghosting artifacts and B1 inhomogeneity artifacts were graded by using a three-point scale, with which a grade of 0 indicated artifact absent; a grade of 1, artifact present but not affecting diagnostic image quality; and a grade of 2, artifact present and impairing diagnostic image quality. Image graininess, or image noise, was defined as to whether the borders of the ductal structures appeared sharp or blurred. This was also graded by using a three-point scale, with which a grade of 0 indicated mild image noise; a grade of 1, moderate image noise; and a grade of 2, severe image noise.
Statistical Analysis
Statistical analysis of the quantitative data involved using the paired Student t test to test the null hypothesis that the CNR was identical with each MR cholangiography sequence. Statistical software (SAS, version 8.2, 2001; SAS Institute, Cary, NC) was used for this purpose. P < .05 was considered to indicate a statistically significant difference.
Statistical analysis of the acquisition time was also performed by using the paired Student t test to test the null hypothesis that the acquisition time was identical for each MR cholangiography sequence. The same software was also used for this purpose, and P < .05 was also deemed to indicate a statistically significant difference.
Subjective data from the DROC analysis were used to test the null hypothesis that the two sequences had equal image quality. The area under the DROC curve was calculated for each reader by using the standard DROC method (9). For the DROC, an area under the curve greater than 0.50 represented a preference for the SPACE sequence, with a value of more than 0.58 being statistically significant at the P = .05 level. A value of less than 0.50 represented a preference for the respiratory-triggered fast SE T2-weighted sequence, with a value of less than 0.42 being statistically significant at the P = .05 level (9). Interobserver agreement was assessed by calculating the Cohen 
statistic for the DROC scores and was described by using the characterization of Altman (10).
Statistical analysis of the N/2 artifacts, B1 inhomogeneity artifacts, and image noise was performed by using the 
2 test to test the null hypothesis that the incidence of each was the same for both sequences. The table used for the 2 test was a 3 x 3 table parameterized by using the three-point grading scales described above. A P value of .05 with the 2 test was considered to indicate a significant difference. Interobserver agreement was again assessed by calculating the Cohen statistic and was described by using the characterization of Altman (10).
|
RESULTS
|
|---|
Quantitative Data Analysis
CNRs between the common bile duct and the periductal tissue and between the intrahepatic bile ducts and surrounding liver parenchyma showed statistically significant differences in all locations, with the CNRs being lower with the SPACE sequence (P < .05 for all locations [Table]).
The mean acquisition time was 4 minutes 57 seconds (range, 3 minutes 14 seconds to 8 minutes 10 seconds) for the standard sequence and 3 minutes 53 seconds (range, 2 minutes 12 seconds to 6 minutes 32 seconds) for the SPACE sequence. The difference in sequence acquisition times (mean time savings with SPACE, 21%) was significant (P < .01).
Note that the CNR difference (33%–36% less with the SPACE sequence [Table]) was essentially the same as the acquired voxel volume difference (36% smaller with the SPACE sequence).
Qualitative Analysis
Both readers independently assessed the overall image quality with the SPACE sequence as superior, with an area under the DROC curve of 0.75 for reader 1 and 0.79 for reader 2. These values indicate that both readers had a statistically significant preference for the SPACE sequence. Agreement was good, with a Cohen value of 0.68.
Artifacts
N/2 ghosting artifacts were seen in images of 14 (48%) of 29 patients by reader 1 and in images of 13 (45%) patients by reader 2 with the 3D fast SE T2-weighted sequence; both readers found these artifacts to affect diagnostic image quality in seven cases (24%) (Fig 2). N/2 ghosting artifacts were not seen with the SPACE sequence by either reader. These differences were statistically significant (P < .01). Interobserver agreement was very good, with Cohen values of 0.83 and 1.00 for the 3D fast SE T2-weighted and SPACE sequences, respectively.
View larger version (77K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 2a: Pancreas divisum in 42-year-old man. (a) Coronal MIP of standard fast SE T2-weighted sequence data (one respiratory cycle/645) shows severe N/2 ghost artifacts of fluid-filled duodenum (short arrows), gallbladder (long arrow), and fluid-filled gastric fundus (arrowheads). Acquisition time = 430 seconds. Ghosting artifact from stomach obscures right hepatic duct. (b) Coronal MIP of SPACE sequence data (one respiratory cycle/746) shows elimination of N/2 ghost artifacts. Arrow = minor pancreatic papilla. Acquisition time = 222 seconds. Right hepatic duct is visualized.
|
|
View larger version (53K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 2b: Pancreas divisum in 42-year-old man. (a) Coronal MIP of standard fast SE T2-weighted sequence data (one respiratory cycle/645) shows severe N/2 ghost artifacts of fluid-filled duodenum (short arrows), gallbladder (long arrow), and fluid-filled gastric fundus (arrowheads). Acquisition time = 430 seconds. Ghosting artifact from stomach obscures right hepatic duct. (b) Coronal MIP of SPACE sequence data (one respiratory cycle/746) shows elimination of N/2 ghost artifacts. Arrow = minor pancreatic papilla. Acquisition time = 222 seconds. Right hepatic duct is visualized.
|
|
B1 inhomogeneity artifacts were more commonly seen with the SPACE sequence; they were seen in images of 13 (45%) of 29 patients by reader 1 and in images of nine (31%) patients by reader 2 (Fig 3). Both readers found that B1 inhomogeneity artifacts affected diagnostic image quality in four cases (14%). By comparison, both readers observed B1 inhomogeneity artifacts in images of only three (10%) of 29 patients with the standard 3D fast SE T2-weighted sequence, and these artifacts affected diagnostic image quality in only one case (3%), according to reader 1 but not reader 2. These differences were statistically significant (P < .01). Interobserver agreement was very good to good, with Cohen values of 0.82 and 0.62 for the 3D fast SE T2-weighted and SPACE sequences, respectively.
View larger version (110K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 3a: Dilated common bile duct after cholecystectomy in 57-year-old woman. (a) Coronal MIP of standard fast SE T2-weighted sequence data (one respiratory cycle/645) shows markedly dilated common bile duct (maximum diameter, 13 mm), which smoothly tapers toward the papilla of Vater. Arrows = pancreatic duct. Acquisition time = 193 seconds. (b) Coronal MIP of SPACE sequence data (one respiratory cycle/746) shows marked signal loss in center of image that represents B1 inhomogeneity artifact. Pancreatic duct is not depicted. Acquisition time = 226 seconds. The dielectric artifact obscures the entire extrahepatic biliary system. There is also suboptimal depiction of the papilla as compared with a.
|
|
View larger version (69K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 3b: Dilated common bile duct after cholecystectomy in 57-year-old woman. (a) Coronal MIP of standard fast SE T2-weighted sequence data (one respiratory cycle/645) shows markedly dilated common bile duct (maximum diameter, 13 mm), which smoothly tapers toward the papilla of Vater. Arrows = pancreatic duct. Acquisition time = 193 seconds. (b) Coronal MIP of SPACE sequence data (one respiratory cycle/746) shows marked signal loss in center of image that represents B1 inhomogeneity artifact. Pancreatic duct is not depicted. Acquisition time = 226 seconds. The dielectric artifact obscures the entire extrahepatic biliary system. There is also suboptimal depiction of the papilla as compared with a.
|
|
Image Quality
Image graininess was present in the images of 10 (34%) of 29 patients according to reader 1 and in the images of eight (28%) patients according to reader 2 with the SPACE sequence; this graininess was severe in two cases (7%) according to reader 1 and in one case (3%) according to reader 2 (Fig 4). By comparison, image graininess was seen by both readers in three (10%) of 29 cases with the standard sequence and was severe in one case according to reader 1 but not reader 2. These differences were statistically significant (P = .02). Interobserver agreement was very good to good, with Cohen values of 0.82 and 0.70 for the 3D fast SE T2-weighted and SPACE sequences, respectively.
View larger version (89K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 4a: Aberrant right segmental biliary duct in 26-year-old woman. (a) Coronal MIP of standard fast SE T2-weighted sequence data (one respiratory cycle/645) shows aberrant right segmental biliary duct (arrows) draining separately into common hepatic duct. Acquisition time = 221 seconds. (b) Coronal MIP of SPACE sequence data (one respiratory cycle/746) appears grainy and shows several pseudo-filling defects (arrows), making the exclusion of the presence of small stones difficult. Acquisition time = 135 seconds.
|
|
View larger version (80K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 4b: Aberrant right segmental biliary duct in 26-year-old woman. (a) Coronal MIP of standard fast SE T2-weighted sequence data (one respiratory cycle/645) shows aberrant right segmental biliary duct (arrows) draining separately into common hepatic duct. Acquisition time = 221 seconds. (b) Coronal MIP of SPACE sequence data (one respiratory cycle/746) appears grainy and shows several pseudo-filling defects (arrows), making the exclusion of the presence of small stones difficult. Acquisition time = 135 seconds.
|
|
Overall, artifacts and image noise limited the diagnostic capability with the SPACE sequence in four cases (14%) according to reader 1 and in five cases (17%) according to reader 2. Diagnostic information with the 3D fast SE T2-weighted sequence was limited by artifacts in nine cases (31%) according to reader 1 and in 10 cases (34%) according to reader 2.
|
DISCUSSION
|
|---|
The use of a whole-body 3.0-T MR imaging system for routine clinical use is usually driven by the anticipated gain in SNR. Increased SNR can be used directly to improve image quality (11). Alternatively, the gain in SNR can also be traded for increased spatial resolution or decreased imaging time. However, not all patients are suitable for imaging at 3.0 T. In particular, images in large patients and in those with ascites are more susceptible to B1 inhomogeneity artifacts.
The mean acquisition time for the standard 3D fast SE T2-weighted sequence was approximately 25% longer (ie, approximately 1 minute longer), with the difference being statistically significant. This corresponds to the fact that the standard sequence requires 54 respiratory cycles (36 partitions times two respiratory cycles per partition times a partial Fourier factor of 0.75) to acquire 36 2-mm-thick partitions, compared with the 42 respiratory cycles (56 partitions times one respiratory cycle per partition times a partial Fourier factor of 0.75) required to acquire 56 1.3-mm-thick partitions with the SPACE sequence.
CNRs between the bile ducts and the periductal tissue were lower with the SPACE sequence. This difference could potentially be attributed to several factors in the SPACE sequence, such as higher spatial resolution (from 2 to 1.3 mm), the longer effective echo time (from 645 to 746 msec), the decreased refocusing pulse flip angle (from a maximum of 180° to a maximum of 120°), the increased receiver bandwidth (from 251 to 751 Hz/pixel), and the implementation of parallel imaging with an acceleration factor of three. The increased number of signals acquired in the SPACE sequence (ie, two [vs one in the standard sequence]), on the other hand, increases SNR, thus counteracting the impact of the other factors to some extent.
Overall, the decreased CNR almost exactly corresponds to the decreased voxel volume (improved spatial resolution) of the SPACE sequence. On the basis of MR physics considerations alone, we would expect the SNR of the source images to be directly proportional to the voxel volume, but the same may not be true of the SNR in the MIP images (12). If we were to compensate for this effect, either retrospectively by normalizing the CNR to the voxel volume or prospectively by using 2-mm-thick voxels (increasing the coverage for SPACE), it would be reasonable to expect to find that the SPACE sequence is more CNR efficient, achieving a similar CNR in a shorter time. However, in this study, such a comparison was not attempted because the extra coverage is not clinically necessary and the volume compensation may not be appropriate for the MIP images.
Despite the measured decrease in CNR, both readers significantly preferred the image quality of the SPACE sequence in a side-by-side comparison. The preference for the SPACE sequence was evident despite the quantitative decrease in CNR and the corresponding increase in graininess discussed above. We attribute the reader preference for the SPACE sequence primarily to the elimination of N/2 ghosting.
B1 inhomogeneity artifacts (also known as dielectric resonance or standing-wave artifacts) were more commonly seen with the SPACE sequence and were considered to affect diagnostic image quality 14% of the time with SPACE. B1 inhomogeneity artifacts are usually not seen at 1.5-T MR imaging but are a well-known problem at 3.0 T. These artifacts are related to the higher-frequency B1 transmit fields that are used at 3.0 T. The wavelength of the radiofrequency field at 128 MHz (Larmor frequency at 3.0 T) is 234 cm in free space, which is much larger than the field of view for clinical body imaging. However, water and most body tissues have a rather high dielectric constant, which reduces both the speed and the wavelength of the radiofrequency field. This effect reduces the radiofrequency field wavelength from 234 cm in free space to about 30 cm in most human tissues—that is, water-containing tissues (12–14). This is on the order of the size of the field of view for many body applications and can result in "standing wave" effects (15). As a result, strong signal intensity variations across an image can be seen—especially brightening in regions away from the receiver coil or dark "holes" caused by constructive or destructive interference from the standing waves. These artifacts tend to become more pronounced when longer echo trains are implemented, as in the SPACE sequence. Improvements in the SPACE sequence will need to address the problem of B1 inhomogeneity artifacts.
N/2 ghosting artifacts, on the other hand, were seen only in images obtained with the fast SE T2-weighted sequence, affected diagnostic image quality more often (24%) than B1 inhomogeneity artifacts, and were present more often than severe image graininess. The standard fast SE T2-weighted sequence is only able to acquire half of the k-space lines per partition in a single respiratory cycle. If there are differences in diaphragm position between the two halves of k-space, N/2 ghost artifacts may appear. The SPACE sequence acquires an entire k-space partition in a single respiratory cycle, eliminating this artifact. Another strategy to decrease ghosting artifacts is the use of oral negative contrast agents (16). However, this would only decrease ghosting artifacts from the stomach and duodenum but would not eliminate ghosting artifacts from the gallbladder. Additionally, the absence of high T2 signal within the duodenum may affect the ability to accurately visualize the entry point of the common bile duct and pancreatic duct in the duodenum (17). There has also been a report of a signal void in the distal common bile duct created by reflux of oral negative contrast agent into the common bile duct in a patient who had undergone a sphincterotomy (17). For these reasons, a sequence-based method for eliminating N/2 ghosting would often be preferable to the use of oral contrast agents.
Image graininess (subjective image noisiness) was more commonly seen with the SPACE sequence, but even so was considered problematic less often (3%–7%) than either B1 inhomogeneity or N/2 ghosting. This subjective finding was reflected in the quantitative data analysis, which revealed lower CNR with the SPACE sequence. The thinner sections of the SPACE sequence probably contributed most to the graininess that was seen on these images. Future studies testing diagnostic accuracy may be able to demonstrate if the advantage of improved resolution outweighs the disadvantage of increased graininess.
There were limitations to our study. First, the study design did not permit us to address the issue of diagnostic accuracy. A prospective study with a larger number of positive cases would have the power to address this issue. Second, the readers in our study were not blinded to the MR imaging sequence type during interpretation and comparison. Although this could have influenced the qualitative comparison (reader preference) somewhat, it was unlikely to influence the detection and measured rates of artifacts for the two sequences.
In conclusion, MR cholangiography with the SPACE pulse sequence eliminates ghosting artifacts and decreases acquisition time at 3.0 T. Readers preferred images obtained with the SPACE sequence to conventional fast SE T2-weighted images despite a decrease in the CNR and some increases in image noise and B1 inhomogeneity artifacts.
|
ADVANCE IN KNOWLEDGE
|
|---|
- The sampling perfection with application optimized contrasts using different flip angle evolutions sequence eliminates ghosting artifacts while maintaining sufficient image quality and contrast-to-noise ratio during MR cholangiography at 3.0 T.
|
IMPLICATION FOR PATIENT CARE
|
|---|
- The elimination of N/2 ghosting artifacts could potentially result in improved diagnostic accuracy for evaluating the biliary ductal system.
|
FOOTNOTES
|
|---|
Abbreviations: CNR = contrast-to-noise ratio • DROC = differential receiver operating characteristic curve • MIP = maximum intensity projection • SE = spin echo • SNR = signal-to-noise ratio • SPACE = sampling perfection with application optimized contrasts using different flip angle evolutions • 3D = three-dimensional
Guarantors of integrity of entire study, C.M.H., E.M.M.; study concepts/study design or data acquisition or data analysis/interpretation, all authors; manuscript drafting or manuscript revision for important intellectual content, all authors; manuscript final version approval, all authors; literature research, all authors; clinical studies, C.M.H., E.M.M.; statistical analysis, B.M.D.; and manuscript editing, all authors
|
References
|
|---|
- Barish MA, Yucel EK, Ferrucci JT. Magnetic resonance cholangiopancreatography. N Engl J Med 1999;341:258–264. [Free Full Text]
- O'Regan DP, Fitzgerald J, Allsop J, et al. A comparison of MR cholangiopancreatography at 1.5 and 3.0 Tesla. Br J Radiol 2005;78:894–898. [Abstract/Free Full Text]
- Merkle EM, Haugan PA, Thomas J, Jaffe TA, Gullotto C. 3.0- versus 1.5-T MR cholangiography: a pilot study. AJR Am J Roentgenol 2006;186:516–521. [Abstract/Free Full Text]
- Hennig J, Scheffler K. Hyperechoes. Magn Reson Med 2001;46:6–12. [CrossRef][Medline]
- Lichy MP, Wietek BM, Mugler JP 3rd, et al. Magnetic resonance imaging of the body trunk using a single-slab, 3-dimensional, T2-weighted turbo-spin-echo sequence with high sampling efficiency (SPACE) for high spatial resolution imaging: initial clinical experiences. Invest Radiol 2005;40:754–760. [CrossRef][Medline]
- Asbach P, Klessen C, Kroencke TJ, et al. Magnetic resonance cholangiopancreatography using a free-breathing T2-weighted turbo spin-echo sequence with navigator-triggered prospective acquisition correction. Magn Reson Imaging 2005;23:939–945. [CrossRef][Medline]
- Klessen C, Asbach P, Kroencke TJ, et al. Magnetic resonance imaging of the upper abdomen using a free-breathing T2-weighted turbo spin echo sequence with navigator triggered prospective acquisition correction. J Magn Reson Imaging 2005;21:576–582. [CrossRef][Medline]
- Schmithorst VJ, Dardzinski BJ, Holland SK. Simultaneous correction of ghost and geometric distortion artifacts in EPI using a multi-echo reference scan. IEEE Trans Med Imaging 2001;20:535–539. [CrossRef][Medline]
- Chakraborty DP, Kundel HL, Nodine C, Narayan TK, Devaraju V. The differential receiver operating characteristic (DROC) method. In: Hanson KM, ed. Proceedings of SPIE: medical imaging 1998—image processing. Vol 3338. Bellingham, Wash: International Society for Optical Engineering, 1998; 234–240.
- Altman DG. Practical statistics for medical research. New York, NY: Chapman & Hall/CRC, 1999; 624.
- Merkle EM, Dale BM, Paulson EK. Abdominal MR imaging at 3.0 Tesla. Magn Reson Imaging Clin N Am 2006;14:17–26. [CrossRef][Medline]
- Haacke EM, Brown RW, Thompson MR, Venkatesan R. Magnetic resonance imaging: physical principles and sequence design. New York, NY: Wiley, 1999;10:662.
- Schick F. Whole-body MRI at high field: technical limits and clinical potential. Eur Radiol 2005;15:946–959. [CrossRef][Medline]
- Kangarlu A, Baertlein BA, Lee R, et al. Dielectric resonance phenomena in ultra high field MRI. J Comput Assist Tomogr 1999;23:821–831. [CrossRef][Medline]
- Collins CM, Liu W, Schreiber W, Yang QX, Smith MB. Central brightening due to constructive interference with, without, and despite dielectric resonance. J Magn Reson Imaging 2005;21:192–196. [CrossRef][Medline]
- Jacobsen TF, Van Beers LM, Dupas B et al. Oral magnetic particles (ferristene) as a contrast medium in abdominal magnetic resonance imaging. Acad Radiol 1996;3:571–580. [CrossRef][Medline]
- Sugita R, Nomiya T. Disappearance of the common bile duct signal caused by oral negative contrast agent on MR cholangiopancreatography. J Comput Assist Tomogr 2002;26:448–450. [CrossRef][Medline]
TOP
ABSTRACT
INTRODUCTION
