Effect of estrogen replacement on the histologic response to polypropylene mesh implanted in the rabbit vagina model.

OBJECTIVE: The aim of this study was to determine the effect of estrogen replacement after ovariectomy on the histologic response to polypropylene mesh implanted in rabbit vagina. STUDY DESIGN: Thirty rabbits were assigned to 5 groups: sham laparotomy, ovariectomy, ovariectomy-preoperative estrogen, ovariectomy-postoperative estrogen, or ovariectomy-preoperative and postoperative estrogen. Rabbits underwent sham surgery or ovariectomy and were infused with vehicle or 17beta-estradiol (200 microg/d) for 4 weeks ("preoperative" estrogen). Polypropylene mesh was implanted in the posterior vaginal wall, and rabbits were infused with vehicle or "postoperative" estrogen for an additional 8 weeks. Grafts were harvested and underwent histologic evaluation. RESULTS: Vaginal atrophy in ovariectomized rabbits was reversed by estrogen replacement. Scores for inflammation (P = .33) and neovascularization (P = .23) at the graft site were not different among estrogen replacement groups, but estrogen administration was associated with increased collagen deposition (P = .005). CONCLUSION: Estrogen replacement administered for 8 weeks postoperatively increases collagen deposition into polypropylene mesh.

Biomechanical properties of synthetic and biologic graft materials following long-term implantation in the rabbit abdomen and vagina.

OBJECTIVE: We sought to evaluate the effects of anatomic location and ovariectomy on biomechanical properties of synthetic and biologic graft materials after long-term implantation. STUDY DESIGN: A total of 35 rabbits underwent ovariectomy or sham laparotomy and were implanted with polypropylene (PP) mesh (n = 17) or cross-linked porcine dermis (PS) (n = 18) in the vagina and abdomen. Grafts were harvested 9 months later and underwent mechanical properties testing. RESULTS: After implantation, PS was similar in strength (P = .52) but was twice as stiff as PP (P = .04) and had a maximal elongation only half that of PP (P < .001). Degradation of PS was associated with decreased ultimate tensile strength (P = .03) and elastic modulus (P = .046). Vaginal PP grafts shrunk more (P < .001) and were less stiff than abdominal PP grafts (P = .049) but were not different in strength (P = .19). Ovariectomy had no effect (P > .05). CONCLUSION: Cross-linked PS undergoes long-term degradation resulting in compromised biomechanical properties and thus is likely inferior to lightweight PP meshes for pelvic organ prolapse and incontinence procedures.

Long-term histologic response to synthetic and biologic graft materials implanted in the vagina and abdomen of a rabbit model.

OBJECTIVE: We sought to evaluate the effects of graft type, site of implantation, and ovariectomy on the long-term histologic response to graft materials used in pelvic reconstructive surgery. STUDY DESIGN: In all, 45 rabbits underwent ovariectomy or sham laparotomy and were implanted with polypropylene (PP) mesh (n = 23) or cross-linked porcine dermis (PS) (n = 22) in the vagina and abdomen. Grafts were harvested 9 months later and were processed for histology to evaluate the host inflammatory response and degree of tissue incorporation within the grafts. RESULTS: Polypropylene induced a milder (P < .007), more uniform response than PS, whereas PS elicited a more variable response and degraded by 9 months. Vaginal grafts had higher scores for inflammation (P = .005) and neovascularization (P < .001), and had lower scores for fibroblastic proliferation (P < .001) than abdominal grafts. Ovariectomy had no effect (P > .05). CONCLUSION: Synthetic and biologic grafts evoke different foreign body responses, which may have implications for surgical outcomes in women.

Histologic response of porcine collagen-coated and uncoated polypropylene grafts in a rabbit vagina model.

OBJECTIVE: The purpose of this study was to determine whether the host tissue response in the rabbit vagina differs for 2 synthetic graft materials that are used in pelvic reconstructive surgery. STUDY DESIGN: One strip of porcine collagen-coated or uncoated polypropylene mesh was implanted adjacent to a sham operative site into the posterior vagina of 10 New Zealand white rabbits and harvested 12 weeks later. Rabbits were assigned randomly to group 1 (coated; n = 5), group 2 (uncoated; n = 5), or group 3 (unoperated; n = 4). Full-thickness sagittal sections of posterior vaginal wall and rectum were scored for inflammation, neovascularization, and fibroblastic proliferation. RESULTS: Erosion of grafts did not occur in any animal. Coated and uncoated meshes induced a mild inflammatory response with minimal fibrosis and good host tissue incorporation within the grafts. Few apoptotic and proliferating cells were seen for both graft types. CONCLUSION: Both coated and uncoated polypropylene meshes elicit a mild foreign body reaction and minimal fibrotic response without evidence of vaginal epithelial erosion.

The efficacy of gadobenate dimeglumine (Gd-BOPTA) at 3 Tesla in brain magnetic resonance imaging: comparison to 1.5 Tesla and a standard gadolinium chelate using a rat brain tumor model.

OBJECTIVES: The objectives of this study were to analyze the differences in contrast enhancement using gadobenate dimeglumine (Gd-BOPTA or MultiHance) at 3 T versus 1.5 T and to compare Gd-BOPTA with a standard gadolinium chelate, gadopentetate dimeglumine (Gd-DTPA or Magnevist), at 3 T in a rat glioma model. MATERIALS AND METHODS: Twelve rats with surgically implanted gliomas were randomized to either comparing Gd-BOPTA at 1.5 T versus 3 T (n=7) or comparing Gd-BOPTA and Gd-DTPA at 3 T (n=5). Matched T1-weighted spin-echo techniques were used for both comparisons and the order of examinations was randomized. Signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), and lesion enhancement (LE) were evaluated using a region-of-interest analysis. A veterinary histopathologist evaluated all brain specimens. RESULTS: In the evaluation of Gd-BOPTA at 3 T and 1.5 T, there were significant increases in SNR, LE, and CNR at 3 T. Average increases in brain and tumor SNR were 93% (P<0.0001) and 92% (P<0.0001), respectively. CNR increased by 121% (P<0.0001). Comparison of Gd-BOPTA and Gd-DTPA at 3 T demonstrated significantly higher CNR and LE with Gd-BOPTA. CNR increased by 35% (P=0.002). LE increased by 44% (P=0.03). CONCLUSIONS: Gd-BOPTA provides significantly higher CNR at 3 T compared with 1.5 T and also demonstrates significantly higher CNR when compared with a standard Gd-chelate at 3 T. As a result of transient protein binding, Gd-BOPTA may be superior to standard gadolinium chelates in neurologic imaging at 3 T.

T1-weighted imaging of the brain at 3 tesla using a 2-dimensional spoiled gradient echo technique.

RATIONALE AND OBJECTIVES: The objective of this study was to evaluate a 2-dimensional spoiled gradient echo (GRE) imaging approach using a very short in-phase TE for routine T1-weighted imaging of the brain at 3 T. MATERIALS AND METHODS: Patient examinations were compared from a 3 T magnetic resonance (MR) unit located immediately adjacent to a similarly equipped 1.5 T unit. Pre- and postcontrast T1-weighted images were evaluated and compared at 1.5 versus 3 T with a 2-dimensional (2-D) spin echo sequence used at 1.5 T and a 2-D GRE sequence at 3 T. The 2 MR systems used are from the same vendor, use similar 8-channel coils, and use identical gradients. The T1-weighted GRE sequence, used at 3 T, relies on a short TE (2.4 ms) to limit flow-related and susceptibility artifacts. Region-of-interest analysis was performed on 16 different sagittal patient examinations at both field strengths (32 total) and similarly on 10 different pre- and postcontrast axial examinations (40 total). Four blinded neuroradiologists also evaluated these studies. RESULTS: Using an off-midline sagittal slice depicting the caudate nucleus (signal-to-noise ratio [SNR] 163 +/- 28 vs. 70 +/- 7, 3 T vs. 1.5 T) and corona radiata (SNR 214 +/- 35 vs. 82 +/- 10), 3 T markedly outperformed 1.5 T in both SNR and contrast-to-noise ratio (CNR) (51 +/- 14 vs. 12 +/- 5). On axial imaging, despite a reduction in slice thickness (5 to 3 mm) and scan time (5 to 1 minute), there was no significant difference pre- or postcontrast in SNR and CNR comparing 3 and 1.5 T. On blinded film review, 3 T performed slightly better on sagittal scans than 1.5 T in regard to motion artifacts (reduced), gray-white matter differentiation, and overall image quality. On axial scans, 3 T performed markedly better in all 3 categories both pre- and postcontrast. In regard to overall image quality, 3 T was preferred 9:2 precontrast and 4:1 postcontrast. CONCLUSIONS: High-quality, thin-section (3-mm) T1-weighted imaging can be readily performed at 3 T using a short TE 2-D GRE technique. This approach offers superior SNR and CNR with reduced motion artifacts and scan time as compared with imaging at 1.5 T and is advocated for routine brain imaging at 3 T. It is robust (used in over 1500 patients to date) and does not experience significant specific absorption ratio limitations, poor tissue contrast, or accentuated motion artifacts like encountered with spin echo T1-weighted imaging at 3 T.

Brain tumor enhancement in magnetic resonance imaging: comparison of signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) at 1.5 versus 3 tesla.

OBJECTIVE: The objective of this study was to compare the difference in lesion enhancement between 1.5 and 3 T using an extracellular gadolinium chelate in a rat brain glioma model. METHODS: Five rats (CDF Fischer 344) with implanted C6/LacZ brain gliomas were evaluated using matched T1-weighted spin echo techniques and hardware configurations at 1.5 and 3 T. Serial imaging over 10 minutes after gadoteridol (ProHance) administration was performed. Contrast enhancement (CE), signal-to-noise ratios (SNR) for brain and tumor, as well as contrast-to-noise ratios (CNR) were evaluated using region-of-interest (ROI) analysis at both field strengths. All gliomas were also evaluated by histopathology. RESULTS: CE at 3 T increased by 106% to 137% (all P<0.05) with maximum CE occurring at 5 minutes for both 1.5 and 3 T (9.8+/-2.2 vs 21.1+/-3.5; P=0.0004). At 3 T, SNR increased for normal brain by 66% to 76% (P<0.01) and SNR for tumor increased by 70% to 89% (P<0.01). CNR increased by 101% to 137% (P<0.05) depending on the time postcontrast. The highest CNR for both 1.5 T and 3 T occurred 5 minutes after contrast (1.5 T: 9.4+/-1.1 vs 3 T: 20.3+/-2.4; P<0.0004). CONCLUSION: Using a standardized animal model and matched scan techniques, this study shows a significant benefit of 3 T compared with 1.5 T in contrast-enhanced brain tumor magnetic resonance imaging.