Magnetic resonance imaging of the uterine cervix using an intravaginal coil

Prospective motion correction using tracking coils

Intracavity imaging coils provide higher signal-to-noise than surface coils and have the potential to provide higher spatial resolution in shorter acquisition times. However, images from these coils suffer from physiologically induced motion artifacts, as both the anatomy and the coils move during image acquisition. We developed prospective motion-correction techniques for intracavity imaging using an array of tracking coils. The system had <50 ms latency between tracking and imaging, so that the images from the intracavity coil were acquired in a frame of reference defined by the tracking array rather than by the system's gradient coils. Two-dimensional gradient-recalled and three-dimensional electrocardiogram-gated inversion-recovery-fast-gradient-echo sequences were tested with prospective motion correction using ex vivo hearts placed on a moving platform simulating both respiratory and cardiac motion. Human abdominal tests were subsequently conducted. The tracking array provided a positional accuracy of 0.7 ± 0.5 mm, 0.6 ± 0.4 mm, and 0.1 ± 0.1 mm along the X, Y, and Z directions at a rate of 20 frames-per-second. The ex vivo and human experiments showed significant image quality improvements for both in-plane and through-plane motion correction, which although not performed in intracavity imaging, demonstrates the feasibility of implementing such a motion-correction system in a future design of combined tracking and intracavity coil.

MRI of female genital and pelvic organs during sexual arousal

We utilized contrast enhanced magnetic resonance imaging (MRI) to delineate the anatomy of the female genital and pelvic organs during sexual arousal. Eleven healthy pre-menopausal women and eight healthy post-menopausal women underwent MRI of the pelvis while watching an erotic video. A 1.5 Tesla MR system was used to produce T1-weighted images following administration of MS-325, a gadolinium-based blood pool contrast agent. Selected structural dimensions and enhancement were measured prior to and during sexual arousal. In both pre- and post-menopausal subjects, vestibular bulb and labia minora width increased with arousal. Enhancement measurements increased in the bulb, labia minora and clitoris in both pre- and post-menopausal subjects, and in the vagina in pre-menopausal subjects. There were no marked changes in size or enhancement of the labia majora, urethra, cervix, or rectum during sexual arousal in pre- or post-menopausal subjects. Using MRI, we observed specific changes in the female genitalia and pelvic organs with sexual arousal, in both pre- and post-menopausal women. MRI can potentially provide detailed anatomical information in the assessment of female sexual function, particularly with regard to changes in blood flow.

Magnetic resonance imaging anatomy of the female genitalia in premenopausal and postmenopausal women

PURPOSE

We used contrast enhanced magnetic resonance imaging (MRI) of the female genital organs to describe normal anatomy and differences between premenopausal and postmenopausal women.

MATERIALS AND METHODS

A total of 12 healthy premenopausal and 9 healthy postmenopausal women underwent MRI. A 1.5 Tesla system with phased array coils anterior and posterior to the pelvis was used to produce T1-weighted images before and after intravenous administration of MS-325 (Epix Medical, Cambridge, Massachusetts), a new gadolinium based blood pool contrast agent. Select structural dimensions were measured for reference.

RESULTS

The clitoris and vestibular bulbs were well delineated on T1-weighted post-contrast images. The clitoral unit formed a brightly enhancing, wishbone-shaped structure lying just anterior to the inverted V of the bulbs, which surrounded the urethra and vagina. The urethral complex had a target-like appearance with layers that were discernible on T1 post-contrast images. The urethra, vagina and rectum formed a distinct complex within uniformly enhancing soft tissue. The vagina was well visualized in premenopausal subjects but without distinguishable mucosal rugae or clearly separate layers in postmenopausal subjects. Postmenopausal subjects were also observed to have smaller labia minora width, vestibular bulb width, vaginal width and wall thickness, and cervical diameter. Pelvic and genital structures were not well visualized on T1 noncontrast images.

CONCLUSIONS

To our knowledge we describe detailed female genital anatomy for the first time using MRI with MS-325 contrast medium. The clitoris, vestibular bulbs, labia majora and minora, urethra, vagina, cervix and rectum are well visualized on T1 post-contrast images. The observed genital anatomy on MRI was consistent with descriptions in current anatomical texts. Differences in the female genitalia between premenopausal and postmenopausal women were discernible on MRI. These data are important for future studies using MRI for evaluating anatomical anomalies, postoperative changes and female sexual function.

Histopathologic correlation of high-resolution magnetic resonance imaging of human cervical tissue samples at 3 tesla: validation of a technique

RATIONALE AND OBJECTIVES

High-resolution magnetic resonance (HR-MR) images of human cervical tissue samples were correlated with low magnification histology to investigate the MR presentation of normal and pathologic anatomic structures in cervical tissue samples at 3T.

METHODS

Tissue samples were obtained from five large loop excision of the transformation zone (LLETZ) cone biopsies and one surgical specimen. HR-MR images (3D-Spin Echo sequence: TR/TE: 1500/60 milliseconds, voxel size of 117 x 208 x 234 microm) and low magnification (5x) histology sections were acquired in the same anatomical planes and correlated.

RESULTS

In vitro HR-MR imaging of cervical tissue samples correlated well with low magnification microscopic histology, demonstrating normal anatomy (epithelium and its mucus layer, connective tissue of the stroma, glands, blood vessels). In vitro HR-MR imaging adds information about tumor content and margins.

CONCLUSIONS

High resolution MR imaging of cervical tissue samples assists in the identification of both normal structures and pathologic changes.

Endourethral MRI

Although high-resolution MRI with phased array pelvic, endorectal, and endovaginal coils has dramatically enhanced the ability to visualize abnormalities of the female urethra and periurethral tissues, controversy still remains about the anatomy of this region. This study introduces an endourethral approach for ultra-high-resolution MRI of the female urethra and the periurethral tissues. To this end, two different radiofrequency (RF) receiver coil designs for an endourethral insertion have been developed: a single-loop coil and a phased array/quadrature coil. Both designs feature a flexible coil circuit, small loss tuning and matching directly at the coil, active decoupling, and the integration of a lambda/4 coaxial choke to decrease unbalanced currents and limit potential RF heating effects. Effective reduction of the mutual inductance between the two coils of the phased array design was achieved by introducing a metallic "paddle" to steer the flux between the coils. The performance of the coils has been evaluated in female human cadaver studies and in an in vivo pig experiment. The novel endourethral approach enabled a dramatic increase of the signal-to-noise ratio (SNR) at the region of interest (ROI). High-resolution MR images of the female urethra have been acquired with a spatial resolution down to 78 x 78 microm. Histologic correlation was achieved for the MR images generated. The achieved high local SNR and resulting high spatial resolution will add valuable information to the discussion of female urethral anatomy. Magn Reson Med 45:138-146, 2001.

Magnetic resonance imaging of the primary site in stage I cervical carcinoma: A comparison of endovaginal coil with external phased array coil techniques at 0.5T

OBJECTIVE

To compare endovaginal with pelvic phased array coil magnetic resonance imaging (MRI) in detection of Stage I cervical carcinoma by correlating the findings with histopathology.

PATIENTS AND METHODS

Forty consecutive patients with Stage I cervical carcinoma confirmed histologically were studied using an endovaginal coil alone immediately followed by a pelvic phased array coil. T1-W transverse and T2-W FSE sagittal images made with each coil were analyzed independently by two radiologists noting the presence and size of a mass within the cervix and any parametrial extension or involvement of adjacent organs. Tumor volumes were measured using the electronic calliper to compute tumor area on each slice and multiplying by the slice thickness. Thirty patients underwent radical hysterectomy, one a trachylectomy, one simple hysterectomy and four extended cone biopsies. Four patients had radiotherapy to the primary tumor. Following surgery, histopathologic findings were recorded and tumor volumes measured.

RESULTS

Tumor volumes ranged from 0-106 cm(3)(median 1.4 cm(3), mean 9 +/- 19.4 cm(3)). Thirty-six patients had correlation of the primary site with the surgical specimen. Agreement between observers was excellent for both endovaginal (k = 0.90) and pelvic phased array (k = 0.96) techniques. Combined sensitivity and specificity for both observers of endovaginal MR imaging for detection of tumor was 96% and 70%, respectively; for pelvic phased array imaging sensitivity was substantially less at 54%. Specificity was higher at 83.7%, probably because small abnormalities were seldom visible. In patients treated surgically, early parametrial involvement in four women on endovaginal MRI was confirmed histologically in two. Pelvic phased array imaging showed early parametrial involvement in four women and was confirmed in one.

CONCLUSION

Endovaginal MRI adds substantially to information from pelvic phased array images in the preoperative assessment of patients with early cervical cancer. J. Magn. Reson. Imaging 2000;12:1020-1026.

Design and use of internal receiver coils for magnetic resonance imaging

This review describes coils for MRI that are inserted into the body through natural orifices. It covers the design and implementation of small internal receiver coils for use in the pelvis and gastrointestinal tract. Normal anatomy delineated by the high resolution obtained by using these coils and the appearances in a number of disease states for each clinical application are described.

Value of magnetic resonance imaging with an endovaginal receiver coil in the pre-operative assessment of Stage I and IIa cervical neoplasia

OBJECTIVE

To assess the value of high resolution endovaginal magnetic resonance images (MRI) of the uterine cervix in planning management of early cervical cancer.

DESIGN

Prospective cross-sectional study.

SETTING

Specialist gynaecological oncology unit of a postgraduate teaching hospital.

PARTICIPANTS

Thirty nine women aged 25-76 years old (mean 42.5 years) with invasive carcinoma Stage I or IIa of the cervix.

METHODS

A ring coil was positioned endovaginally around the cervix. Imaging was performed on a 1.0 T HPQ Vista or 0.5 T Asset (Picker, Highland Heights, Ohio, USA) using T1 weighted and T2 weighted sequences in transverse and sagittal planes with thin slices (2.5 mm) and small fields of view (12 cm). Tumour volumes were measured and any extension into adjacent organs and parametrium was noted. The patients were followed up after treatment and the outcome related to the MRI findings.

RESULTS

There was one false positive and one false negative result among five Stage Ia patients being assessed for residual disease after cone biopsy or LLETZ. The MRI assessment of the size and distribution of the tumour was confirmed histologically in all 31 patients with Stage Ib or IIa disease who were treated surgically. One of these patients in whom no endocervical tumour was visible on MRI underwent radical trachelectomy. Three patients had radiotherapy as primary treatment. Patients with Stage Ib or IIa disease who had tumour volumes > 10 cm3 with early parametrial extension on MRI had a substantially worse prognosis at 24 months (disease-free survival 58.3% vs 95.5%, P = 0.003).

CONCLUSION

High resolution MRI with an endovaginal coil allows precise measurement of tumour volume and identifies patients with small volume disease who might be considered for more conservative therapy. This technique also reveals early parametrial invasion that cannot be identified reliably by any other method. Early parametrial invasion in women with large tumours appears to have a very much worse prognosis.

MR evaluation of cervical cancer in hysterectomy specimens: correlation of quantitative T2 measurement and histology

Specimens from modified radical hysterectomies performed for invasive carcinoma of the cervix were analyzed with quantitative T2 magnetic resonance (MR) imaging and histologic study to determine to what degree there was a correlation between the findings of the two modalities. The mean T2 of cervical stroma was 48 msec, while the outer zone of the cervix had a mean T2 of 62 msec and the central canal region typically had T2 values of 115 msec +/- 20 (standard deviation). A total of nine cervical cancers were analyzed, and their mean T2 value was 79 msec. Separation between cervical stroma and tumor was good, with stromal T2 values ranging from 30 to 66 msec, while tumor T2s ranged from 60 to 97 msec. Statistical analysis indicated that these data were associated with a sensitivity of 89% and a specificity of 95%, with 95% confidence intervals of [50%, 99.4%] and [74%, 99.7%], respectively, for separating tumor from stroma on the basis of T2 value. Quantitative T2 imaging was found to provide an effective, nonsubjective means of classifying cervical anatomy and neoplastic disease.

Intravascular MR imaging in a porcine animal model

An opposed solenoid intravascular receiver coil is used in a series of five pigs to generate images of the aorta. Severe ghosting artifacts are shown to occur if the motion of the intravascular coil is not restricted with respect to the vessel wall. Restricting coil motion and saturating the blood signal superior to the imaging plane are shown to produce high quality MR images. Layers within the artery wall could be discerned and the results of the in vivo analysis compared favorably with high resolution MR images of the corresponding tissue after excision.

A birdcage resonator for intracavitary MR imaging

An intracavitary probe for magnetic resonance imaging of the pelvis has been developed that takes advantage of the "inside-out" spatial characteristics of a birdcage resonator. The probe consists of an eight-leg, birdcage resonator in a low-pass configuration operating in receive-only mode. The resonator circuit is mounted on a solid rod, is encased in Teflon, and has been used to obtain detailed images of pelvic anatomy in a male canine. The approximate cylindrical symmetry of the external sensitivity profile of this type of circuit, employed in an intracavitary application, demonstrates the potential superiority of this type of probe design over single-loop intracavitary coils. Axial, coronal, and sagittal MR images, obtained with 8 and 16 cm fields of view, are presented to illustrate the advantages of this type of intracavitary probe compared with conventional body-coil images. The prototype described in this report has been designed for clinical use in human subjects and is currently undergoing testing to determine its efficacy in the evaluation of rectal, prostate, and gynecologic pathology.