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Genitourinary Imaging |
1 From the Departments of Radiology (T.M., M.K., S.K., T.I.) and Obstetrics and Gynecology (S.N.), Seirei Hamamatsu General Hospital, 2-12-12 Sumiyoshi, Hamamatsu, Shizuoka 430-8558, Japan; Application Research Group, GE Yokogawa Medical Systems, Hino, Japan (A.N.); and Department of Radiology, Hamamatsu University School of Medicine, Japan (H.S.). Received August 14, 2000; revision requested October 3; final revision received April 3, 2001; accepted April 9. Address correspondence to T.M. (e-mail: masui@sis.seirei.or.jp).
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTS DISCUSSIONREFERENCES |
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MATERIALS AND METHODS: Sagittal MR imaging was performed with T2-weighted fast spin-echo (FSE) and multiphase-multisection single-shot FSE (SSFSE) in 60 premenopausal patients during free breathing. SSFSE MR images were evaluated with cine display. The pattern of uterine contractions and changes in signal intensities of the uterine structures were evaluated. Thickness of both myometrium and junctional zone, and their signal intensities, were measured during 15 phases of SSFSE and FSE MR imaging.
RESULTS: Slow-massive (mean, 55%), middle-cycle (mean, 80%), and fine (mean, 93%) contractions were observed. Shape of junctional zones dynamically changed during time, showing focal (mean, 58%) and diffuse (mean, 82%) thickening and wavelike motions (mean, 88%). Ratio of thickness of the myometrium to junctional zone with FSE MR imaging was not significantly different from the mean ratio during 15 phases of SSFSE MR imaging, although maximum percentage of change of the ratio during 15 phases was 42.5%–56.8%. The signal intensities of the myometrium (97%) and junctional zone (75%) changed during time.
CONCLUSION: Kinematic T2-weighted SSFSE MR images demonstrate uterine contractions related to dynamic changes in thickness and signal intensities of the myometrium and junctional zone, and these findings might affect the diagnosis of uterine disease.
Index terms: Uterus, anatomy, 854.92 • Uterus, MR, 854.121411 • Uterus, myometrium, 854.92
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS DISCUSSIONREFERENCES |
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Uterine contractions, which may have several patterns in pregnant or nonpregnant subjects, have been demonstrated at sonography (5–8). The uterine contraction is recognized as one of the causes of the appearance of pseudolesions on T2-weighted MR images (9,10). This might be due to slow contraction because the effect of the contraction can be visualized as a low-signal-intensity area on T2-weighted MR images, which are usually obtained in about 3–5 minutes (9,10).
With fast MR imaging, fine and slow-massive contractions can be demonstrated as changes in the shape of the uterus and the thickness of the uterine muscle. Because T2-weighted fast imaging provides tissue contrast that demonstrates the zonal anatomy of the uterus, the dynamic effects of uterine contractions on signal intensities during time also can be evaluated.
Accordingly, the purpose of this study was to demonstrate uterine contractions in premenopausal women by evaluating changes during time in the thickness of the myometrium and junctional zone and in signal intensity of the uterus with T2-weighted fast MR imaging in a kinematic fashion.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS DISCUSSIONREFERENCES |
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Patients
From August 1999 to October 1999, 92 consecutive female patients, who were referred by physicians for suspected pelvic pathologic abnormalities after abdominal or transvaginal sonography, underwent pelvic MR imaging. Thirty-two of these patients were excluded because of a history of hysterectomy (n = 4), postmenopausal state (n = 26), or failure to complete the MR study (n = 2). Thus, 60 patients were included in the study. They ranged in age from 16 to 50 years (mean, 42.4 years). Final diagnoses were leiomyoma (n = 27), adenomyosis (n = 13), endometrial cancer or hyperplasia (n = 3), ovarian tumor or cysts (n = 33), and normal (n = 2). Among them, one patient had three diagnoses; 16 had two diagnoses; and the other 43, including patients with normal results, had one diagnosis each. In 29 patients, a surgical or laparoscopic procedure was performed, and, in the remaining 31 patients, final diagnoses were made clinically on the basis of findings at transvaginal sonography, findings during the clinical course, or results of laboratory tests, or of all three.
MR Imaging
MR imaging was performed by using a 1.5-T system (Horizon LX EchoSpeed; GE Medical Systems, Milwaukee, Wis) with a torso phased-array multicoil.
After localization, an antiperistaltic drug (7.5 mg of timepidium bromide, Sesden; Tanabe Seiyaku, Osaka, Japan) was administered intravenously to the patients, who had no contraindications to receiving this drug. Sagittal T2-weighted fast spin-echo (FSE) MR imaging was performed without breath holding by using the following imaging parameters: repetition time msec/effective echo time msec of 4,000/85, echo train length of 16, section thickness of 5 mm, with a 1-mm intersection gap, receiver bandwidth of 32 kHz, matrix of 256 x 256, with 512 zero filling interpolation (apparent resolution, 512 x 512), field of view of 26 x 19 cm, and two signals acquired. A chemical shift fat-saturation pulse was applied. Imaging time was 2 minutes 8 seconds for 20 sections.
Then, 10–15 minutes after the start of T2-weighted FSE MR imaging, sagittal multiphase-multisection T2-weighted SSFSE MR imaging with half-Fourier acquisition was performed without breath holding to cover the whole pelvis. Imaging parameters were as follows: 17,000–28,000/94, echo train length of 85, section thickness of 5–6 mm, intersection gap of 1–2 mm, receiver bandwidth of 62.5 kHz, matrix of 256 x 160, field of view of 35 x 21–24.5 cm, and one-half signal acquired. Imaging time for one phase was 17–28 seconds for 20–26 sections, which were obtained from right to left in an interleaved fashion. Fifteen sequential phases of images were acquired during 5–7 minutes.
Evaluation
All qualitative evaluations for rating were made separately and independently by two radiologists (T.M, M.K.) who were unaware of the clinical symptoms, clinical data, diagnosis, or data of other observers’ evaluations. After a preliminary session for consensus of qualitative rating, each qualitative evaluation of SSFSE and FSE MR images was performed in separate sessions. Quantitative evaluations, such as measurements of the signal intensity and thickness of the structures, were performed jointly by the technologist with one of the authors (T.M.). These evaluations of FSE and SSFSE MR images were performed in a single session.
Display
SSFSE MR images were downloaded onto a workstation (Advantage Windows, version 3.1; GE Medical Systems) and sorted by location. At each location, images were sorted according to time. The images that covered the uterus (a total of 120–300 images; mean, 185 images) were selected and displayed on a screen monitor in a cine loop mode, initially at 10 frames per second and then at 5 and 2 frames per second. For the comparison of SSFSE and FSE MR images and measurements of the thickness and signal intensities, the images were displayed in a static mode.
Image quality and clarity of the uterine zonal anatomy.—A comparison of SSFSE and FSE MR imaging was made on the basis of the following features at SSFSE MR imaging in a cine display and at FSE MR imaging in a static display: Blurring or ghosting artifacts were ranked as 1, severe, where the anatomic structures were difficult to identify because of blurring of the edges or because of artifacts in the phase-encoding direction; as 2, moderate, where the definition of the anatomic structures was poor because of motion or ghosting artifacts; as 3, mild, where lesser degrees of artifacts were noted than at the moderate level; or as 4, none, where there were no motion or ghosting artifacts.
Overall quality of images was ranked as 1, poor, where a diagnosis could not be made due to motion or poor signal intensities of the structures; as 2, acceptable, where the images were diagnostic but there were moderate motion artifacts, poor signal-to-noise ratios (SNRs), or incomplete fat suppression on FSE MR images; as 3, good, where there were some motion artifacts or poor SNRs but less than at the acceptable level; or as 4, excellent, where there were no motion artifacts, SNRs were good, and there was complete suppression of the fat signal intensity on FSE MR images.
Confidence in recognition of zonal anatomy of the uterus (myometrium, junctional zone, and endometrium) was rated as follows: 1, none; 2, poor; 3, moderate; or 4, excellent. The presence of leiomyoma and adenomyosis was also evaluated and rated as follows: 1, definitely absent; 2, probably absent; 3, probably present; or 4, definitely present. The indicator for the existence of the leiomyoma was well-delineated focal low signal intensities, with or without high signal intensities, and that for adenomyosis was ill-defined low signal intensities, with or without high-signal-intensity spots in the uterus (11), especially on SSFSE MR images where low signal intensities should persist during all 15 phases of imaging.
A comparison of SSFSE and FSE MR imaging also was made on the basis of signal intensity measurements. On the SSFSE MR images in the first phase, which demonstrated the myometrium, junctional zone, and endometrium, the region of interest (ROI) was placed on each anatomic structure, and signal intensities of ROIs were measured on each image at the corresponding location during 15 phases of imaging. The ROI ranged from 30 to 110 mm2 (mean, 63.0 mm2 ± 27.2 [SD]) for the myometrium, leiomyoma, and adenomyosis and from 24 to 90 mm2 (mean, 50.0 mm2 ± 21.1) for the junctional zone and endometrium. In the myometrium, the ROI was placed at the area, which may have different signal intensities during 15 phases of imaging. The SD of the signal intensities of air as a background was obtained for the SNR, which was calculated with signal intensities of the structures divided by the SD of the air signal intensity. Subsequently, ROIs were placed on the FSE MR images corresponding to those on SSFSE MR images, and their signal intensities were measured.
Respiratory and peristaltic motion and uterine contractions in SSFSE MR imaging.—Respiratory motion and peristaltic motion of the small intestine were evaluated. These types of motion were ranked as 1, none; 2, slight; 3, mild; 4, moderate; or 5, prominent. Respiratory motion was regarded as movement of the anterior abdominal wall and organs in anteroposterior and superoinferior directions in accordance with diaphragmatic motions. Peristalsis of the small intestine was characterized by waves of alternate circular contraction and relaxation.
Uterine myometrial contraction was evaluated. Uterine contractions were categorized into three groups: (a) slow-massive contractions, with one to three motions during 15 phases of imaging with changes in uterine shape; (b) middle-cycle contractions, with four to 13 motions; or (c) fine contractions, with 14 or 15 subtle motions. Slow-massive and middle-cycle contractions were evaluated by using a five-point scale: 1, none; 2, slight; 3, mild; 4, moderate; or 5, prominent. Fine contractions were evaluated with a three-point scale: 1, none; 2, mild; or 3, prominent. The uterine motions, which had apparent frequencies different from those of respiratory movement or intestinal peristalsis, were considered to be contractions. Positive findings of slow-massive and middle-cycle contraction were ranked as 4 and 5, respectively, and those of fine contraction were ranked as 3.
Changes in the thickness and shape of the uterine junctional zones were evaluated. The patterns of thickness changes in the junctional zone were categorized into three groups: (a) focal thickening during some of the 15 phases; (b) diffuse thickening in the anterior, posterior, or whole uterine walls; and (c) wavelike motions showing continuous subtle motions or fibrillations during 15 phases of imaging. These changing patterns were ranked as 1, none; 2, mild; or 3, prominent; they could be independently recognized in a kinematic display. A rank of 3 was regarded as a positive finding.
The thickness of the myometrium and of the junctional zone was measured. One image, which showed the uterine cavity, was selected from among the multisection SSFSE MR images during the first phase of imaging, and the corresponding images were selected from the FSE and from among SSFSE MR images during the remaining phases of imaging. A line was drawn between two points, the center of the internal cervical os and the fundal portion of the uterine cavity, on these selected images (Fig 1). Lines were then drawn at one-third and two-thirds of the distance perpendicular to the initial line. Four locations on these lines were defined: upper anterior, upper posterior, lower anterior, and lower posterior (Fig 1).
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Changes in signal intensity of the uterine structures were evaluated. Visual assessment of signal intensity changes in the myometrium, junctional zone, endometrium, anterior abdominal wall (rectus abdominis muscle), leiomyoma (n = 27), and adenomyosis (n = 13) during time was made by using a four-point scale (ranging from 1, none, to 4, prominent). Signal intensity changes in the myometrium were further subcategorized into two patterns: diffuse flashlike signal intensity changes and focal signal intensity changes. A four-point scale (raging from 1, none, to 4, prominent) was used to evaluate patterns of signal intensity changes in the myometrium. The positive findings of signal intensity changes were ranked as 3 and 4.
Measurement of the signal intensities of the uterine structures was performed. The signal intensities of the ROI in the myometrium, junctional zone, endometrium, and rectus abdominis muscle were measured on SSFSE images, as described before. The signal intensities of the rectus abdominis muscle were measured by using the ROI (range, 40–100 mm2; mean, 63.0 mm2 ± 31.6). For evaluation of the signal intensity changes, coefficients of variation were calculated as follows: SDSImean/SImean x 100, where SDSImean represents the SDs of the mean signal intensities of the structures during 15 phases of imaging and SImean represents the mean signal intensities of the structures during 15 phases of SSFSE MR imaging.
Statistical Analysis
The ranks obtained in qualitative evaluations by each observer were averaged, and the calculated data were used as the final results. Comparisons of rank in the qualitative assessment between FSE and SSFSE MR images were made by using the Wilcoxon signed rank test. SNRs of the structures (signal intensities divided by the SD [background]) on the SSFSE MR images were compared with those on the FSE MR images with the paired Student t test.
The SNRs of SSFSE MR images were represented as means of the SNRs during 15 phases of imaging. The thickness of the myometrium and junctional zone and the ratio of the thickness of the myometrium to junctional zone on FSE MR images were compared with the mean values during 15 phases of SSFSE MR imaging at four locations by using repeated measures analysis of variance (unstructured). Coefficients of variation of the signal intensities of each structure were compared with those of the rectus abdominis muscle with the F test. A P value of less than .05 was regarded as significant.
A 
coefficient and the standard error of the statistic were calculated to measure the agreement between the two observers in the qualitative evaluation for ranks (12). The level of the agreement was defined with the following values: 0–0.20, poor; 0.21–0.40, fair; 0.41–0.60, moderate; 0.61–0.80, good; and 0.81 >.99, almost perfect (13). All statistical analyses were made by using statistical software programs (SPSS for Windows, SPSS, Chicago, Ill; SAS, SAS Institute, Cary, NC; Excel 98, Microsoft, Redmond, Wash).
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS DISCUSSIONREFERENCES |
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= 0.92 ± 0.08 [mean ± standard error]; artifacts, 4.0 ± 0.2; agreement, 98% [59 of 60 cases]). For acquisition of FSE MR images, an antiperistaltic drug was administered to the 57 patients, who had no contraindications to receiving this drug. Motion artifacts caused by peristalsis of the intestine were not significant, and, in all cases, image quality was acceptable and of diagnostic quality (ranks of quality, 3.9 ± 0.3; = 0.90 ± 0.10; artifacts, 4.0 ± 0.2; agreement, 97% [58 of 60 cases]). There was no significant difference in motion artifacts or image quality between SSFSE and FSE MR images (P > .99). The zonal anatomy of the uterus was equally identified on both images (Table 1, Fig 2).
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Motion and Uterine Contractions
Respiratory motion and peristaltic motion.—In the cine display, respiratory motion was identified as random movement of the abdominal wall and slight upward and downward movements of the viscera. Peristalsis of the small intestine was identified in all cases (Table 2). There was fair agreement between the two observers regarding recognition of respiratory motion and peristaltic motion of the intestine (Table 2).
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= 0.67 ± 0.90) were observed more frequently than were focal signal changes (2.9 ± 1.6 [mean, 62%], = 0.58 ± 0.08) (Figs 2–4). In some cases, signal intensity changes in the myometrium appeared to mimic the signal intensities of adenomyosis or leiomyoma.
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS DISCUSSIONREFERENCES |
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Dynamic imaging of the pelvic floor or pelvic organs by using single-level multiphase acquisitions has been reported (19,20). When configuration changes of the uterus occur with contractions, partial-volume effects of the structures may result in the appearance of pseudolesions or focal thickening of the junctional zone. In the current study, multiphase and multisection imaging was performed to cover the whole pelvis. By reviewing multisection images, a clear differentiation was made by excluding partial-volume effects. By using images randomly obtained without triggering and by retrospectively sorting the data by location and time, the pattern of uterine contractions was evaluated.
One of the limitations of the current study was in the evaluation of the myometrium and junctional zone of the patients with disease. In these patients, lesions such as leiomyoma and adenomyosis might affect the normal range of the thickness, and some large intrauterine or extrauterine lesions might affect the frequency and amplitude of the uterine contractions. However, even in the population of this study, the dynamic changes of the myometrial and junctional zone were frequently observed.
Uterine contractions have been identified at sonography, and directional changes of the contraction during a menstrual cycle have been reported (5–7,21). Some uterine contractions occur in a short timescale, or approximately three to four contractions per minute (5,21); thus, directional motion could not be detected with the current settings for temporal resolution (maximum, three images per minute). However, this type of contraction could be recognized as a random change in the shape and thickness of the myometrium.
Respiratory motion and intestinal peristalsis were also identified as random motions. Findings in this study revealed that slow-massive, middle-cycle, and fine uterine contractions were frequently observed in 55%, 80%, and 93% of patients, respectively. The slow-massive contraction with uterine deformity may be similar to the squeezing motion at labor, and this may be related to the appearance of pseudolesions that mimic adenomyosis or leiomyoma on static T2-weighted MR images (9,10). Fine movement of the uterus may be related to the contractions that have been reported at sonography (6,7,21). This contraction might move from fundus to cervix, or vice versa, as reported in sonographic studies (7,21).
With the current imaging protocol, the frequency of fine and middle-cycle contractions could overlap in some patients. We regarded the uterine contractions as the motions, apparent frequencies, and directions that were different from those of respiration or intestinal peristalsis. However, the effects of respiration and intestinal peristalsis on uterine motions cannot be completely excluded. Thus, for evaluation of the subtle changes of the contraction, further studies with a breath-hold maneuver or use of an antiperistaltic drug are necessary.
There is no general agreement about the physiologic meaning of these contractions, but in the sonographic studies, the directional motion of the uterus is speculated to be related to sperm transport and the conservation of early pregnancies (7). The thickness of the myometrium and junctional zone and the myometrium-to-junctional zone ratios obtained on T2-weighted FSE MR images corresponded with the mean values obtained on T2-weighted SSFSE MR images during the 15 phases of imaging, although maximum and minimum values on SSFSE MR images were substantially different from those on FSE MR images. Thus, the widely used T2-weighted FSE MR images, which take about 3–5 minutes to obtain, may provide summary information and an average of the thickness and signal intensities of the uterine structures.
On MR images, the junctional zone is important in the diagnosis of uterine abnormalities (22,23). Diffuse thickening of the junctional zone has been accepted as one of the findings for adenomyosis (24–26). Findings of histologic studies have demonstrated that myocytes in the junctional zone are characterized by a higher cellular density and a lower cytoplasmic-nuclear ratio than those in other areas of the myometrium (27–29). Other histologic approaches may be required, however, for a thorough evaluation of the junctional zone, which exhibits dynamic functional changes, as indicated in this study. It is known that the thickness of the junctional zone changes with the menstrual cycle (30). Findings in sonographic studies suggest that subendometrial or junctional zone contractions are also dependent on the menstrual cycle or on the levels of certain hormones (5–7,21).
Contraction of the uterus induced changes in the signal intensity of the myometrium and junctional zone both subjectively and objectively. Findings in studies demonstrate that exercise increases signal intensities in the skeletal muscle on T2-weighted MR images (31), but the mechanism of exercise is different from that found in smooth muscle with uterine contraction, which induces low signal intensities during time. Changes during time in signal intensities of the myometrium may be related to blood volume and supply in the muscle (10). The signal intensity changes observed on SSFSE MR images were not induced by motion itself because there was no change in signal intensity of the abdominal wall, which moves with respiration. The artifacts caused by intestinal and abdominal wall motions also were negligible.
In conclusion, kinematic T2-weighted SSFSE MR images demonstrate uterine contractions that are related to dynamic changes in thickness and in signal intensities of the myometrium and junctional zone, and these findings might affect the diagnosis of uterine disease.
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FOOTNOTES |
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Author contributions: Guarantor of integrity of entire study, T.M.; study concepts and design, T.M.; literature research, T.M., M.K., S.K.; clinical studies, T.M., M.K., S.K., S.N.; data acquisition, T.M., M.K., S.K., A.N., H.K.; data analysis/interpretation, T.M., M.K., S.K.; statistical analysis, T.M.; manuscript preparation, T.M.; manuscript definition of intellectual content, T.M., T.I.; manuscript editing and revision/review, T.M., M.K., H.S.; manuscript final version approval, T.M., H.S.
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS DISCUSSIONREFERENCES |
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) also change during time. FSE indicates an FSE image. 1-15 indicate the 15 phases of SSFSE MR imaging.
= myometrium, * = junctional zone, 
= rectus abdominis muscle, + = endometrium.