Gadolinium mesoporphyrin as an MR imaging contrast agent in the evaluation of tumors: an experimental model of VX2 carcinoma in rabbits

Saturation transfer properties of tumour xenografts derived from prostate cancer cell lines 22Rv1 and DU145

Histopathology is currently the most reliable tool in assessing the aggressiveness and prognosis of solid tumours. However, developing non-invasive modalities for tumour evaluation remains crucial due to the side effects and complications caused by biopsy procedures. In this study, saturation transfer MRI was used to investigate the microstructural and metabolic properties of tumour xenografts in mice derived from the prostate cancer cell lines 22Rv1 and DU145, which express different aggressiveness. The magnetization transfer (MT) and chemical exchange saturation transfer (CEST) effects, which are associated with the microstructural and metabolic properties in biological tissue, respectively, were analyzed quantitatively and compared amongst different tumour types and regions. Histopathological staining was performed as a reference. Higher cellular density and metabolism expressed in more aggressive tumours (22Rv1) were associated with larger MT and CEST effects. High collagen content in the necrotic regions might explain their higher MT effects compared to tumour regions.

Lymph node metastases from gastric cancer: gadofluorine M and gadopentetate dimeglumine MR imaging in a rabbit model

PURPOSE

To compare the diagnostic performance of gadofluorine M with that of gadopentetate dimeglumine in the diagnosis of lymph node metastases with magnetic resonance (MR) imaging in a rabbit model of gastric cancer.

MATERIALS AND METHODS

The study protocol was approved by the institutional animal care committee. VX2 carcinomas were inoculated into the wall of the stomach in 20 rabbits. Gadopentetate dimeglumine-enhanced MR imaging was performed 4-6 weeks after inoculation, and gadofluorine M-enhanced MR imaging was performed approximately 24 hours later. Both MR imaging sets were analyzed separately and independently by four radiologists with respect to confidence level regarding the presence of metastases in lymph nodes and lymph node conspicuity. Statistical analysis was performed by using multiple-reader multiple-case (MRMC) receiver operating characteristic curve analysis and the Wilcoxon signed rank test.

RESULTS

Metastases were confirmed at pathologic analysis in 32 of 104 lymph nodes from 16 rabbits. The area under the receiver operating characteristic curve (AUC) for confidence regarding the presence of metastases in lymph nodes was significantly greater for gadofluorine M than for gadopentetate dimeglumine (AUC, 0.947 vs 0.894; P = .009). However, most (81%, 25 of 32) metastatic nodes were necrotic, and no significant difference was obtained in nonnecrotic nodes. For lymph node conspicuity, the gadofluorine M MR imaging set was assigned a significantly higher score than was the gadopentetate dimeglumine MR imaging set by all readers (P < .001).

CONCLUSION

Gadofluorine M showed significantly higher accuracy and better conspicuity than gadopentetate dimeglumine in the diagnosis of metastatic nodes, most of which were necrotic, in this animal model of gastric cancer.

Evolution of VX2 carcinoma in rabbit tibia: magnetic resonance imaging with pathologic correlation

OBJECTIVE

To evaluate the evolution of a metastatic bone tumor model with MRI-pathology correlation.

MATERIALS AND METHODS

VX2 carcinoma was implanted into the tibiae of 20 rabbits. The rabbits were divided into four groups of five (Groups I-IV). MRI was repeated at 1-week interval up to the fourth week, including sagittal T1-weighted image (T1WI), T2-weighted image (T2WI), gadolinium-enhanced fat-suppressed T1WI (GdT1WI), and diffusion-weighted image (DWI). Each group was sacrificed after the imaging, then histological examination for the tibiae with an implanted tumor was performed and MRI-pathologic correlation was done.

RESULTS

On MRI-pathology correlation, the corresponding findings were as follows; low SI on T1WI, T2WI-tumor cells, fibrosis (1 week); central low SI on T1WI, T2WI, GdT1WI -tumor cells with fibrosis and necrosis; peripheral high SI on T2WI, DWI, GdT1WI-edema, fibrosis (2 weeks); heterogeneous SI with central low SI on T2WI, DWI-tumor cell nests with extensive necrosis, fibrosis; high SI on T2WI along periosteum-periosteal reaction; high SI around low SI and in bone marrow on T2WI, DWI, GdT1WI-edema, fibrosis; low SI on T1WI in surrounding bone marrow-tumor extension (3-4 weeks).

CONCLUSION

The evolution of VX2 carcinoma model was well depicted on MR imaging. Necrosis and extent of tumor were best depicted on enhanced, fat-suppressed T1-weighted images. Heterogeneity of the tumor, peripheral edema, and fibrosis were represented well on T2-weighted images. Diffusion-weighted imaging could have a role in depicting necrosis in the evaluation of bone tumor.

Establishment of a rabbit model of superior vena cava obstruction

OBJECTIVE

To explore a method of establishing a rabbit model of superior vena cava obstruction (SVCO) by injecting VX2 tumor cell suspension transcutaneously under ultrasound guidance.

METHODS

A suspension of VX2 tumor cells was prepared under sterile conditions. Fifteen adult healthy New Zealand White rabbits were enrolled in the experiment. Under ultrasound guidance, about 0.1 ml of the living tumor cell suspension was transcutaneously injected in front of the anterior wall of the right superior vena cava (SVC). The lumen, wall, blood flow of SVCs and adjacent tissues were examined with gray-scale and color Doppler ultrasonography, every 3 days starting from the 9th day after injection. Meanwhile, CT scanning and digital subtraction angiography (DSA) were also performed. The rabbits were dissected immediately after death and tissue samples were collected for pathologic examination.

RESULTS

Fourteen out of 15 rabbits developed tumors that were located close to SVCs and/or SVCs cavity, which was shown by ultrasonography. The diameters of the tumors were 80.7 +/- 4.3 mm. These tumors grew close to SVCs area and resulted in compression and infiltration of SVCs. CT scanning and DSA confirmed the establishment of the SVCO model. The achievement rate of the SVCO model was 93.3%. No rabbit died of complications.

CONCLUSION

A method of establishing a rabbit SVCO model by injecting VX2 tumor cell suspension under ultrasonographic guidance was established successfully, and it proved to be simple, effective and repeatable. The imaging characteristics of this model are in good accordance with those of SVCO in patients.

Magnetic resonance imaging after radiofrequency ablation in a rodent model of liver tumor: tissue characterization using a novel necrosis-avid contrast agent

We exploited a necrosis-avid contrast agent ECIV-7 for magnetic resonance imaging (MRI) in rodent liver tumors after radiofrequency ablation (RFA). Rats bearing liver rhabdomyosarcoma (R1) were randomly allocated to three groups: group I, complete RFA, group II, incomplete RFA, and group III, sham ablation. Within 24 h after RFA, T1-weighted (T1-w) MRI was performed before and after injection of ECIV-7 at 0.05 mmol/kg and followed up from 6-24 h. Signal intensities (SIs) were measured with relative enhancement (RE) and contrast ratio (CR) calculated. The MRI findings were verified histomorphologically. On plain T1-w MRI the contrasts between normal liver, RFA lesion, residual and/or intact tumor were vague. Early after administration of ECIV-7, the liver SI was strongly enhanced (RE=40-50%), leaving the RFA lesion as a hypointense region in groups I and II. At delayed phase, two striking peri-ablational enhancement patterns appeared (RE=90% and CR=1.89%), i.e., "O" type of hyperintense rim in group I and "C" type of incomplete rim in group II. These MRI manifestations could be proven histologically. In this study, tissue components after RFA could be characterized with discernable contrasts by necrosis-avid contrast agent (NACA)-enhanced MRI, especially at delayed phase. This approach may prove useful for defining the ablated area and identifying residual tumor after RFA.

High-dose Gd-DTPA vs. Bis-Gd-mesoporphyrin for monitoring laser-induced tissue necrosis

PURPOSE

To compare Bis-Gd-mesoporphyrin (Bis-Gd-MP), a contrast agent with a reported high affinity to necrotic tissue, with high-dose gadopentate dimeglumin (Gd-DTPA) for defining laser-induced muscle and liver necrosis by contrast-enhanced (CE) MRI.

MATERIALS AND METHODS

Laser-induced interstitial thermotherapy (LITT) was performed in the muscle and liver tissue of New Zealand White rabbits (1500 J and 2100 J; n=80 lesions). The animals were randomly assigned to a group that received 0.3 mmol/kg bw Gd-DTPA or a group that received 0.05 mmol/kg bw Bis-Gd-MP. Following contrast injection, dynamic MRI was performed on muscle lesions with a T1-weighted, two-dimensional, fast low-angle shot (FLASH) sequence. The liver and muscle lesions were then repeatedly imaged for six hours after contrast injection using a T1-weighted spin-echo (SE) sequence. Central and peripheral lesion enhancement was determined and correlated with gross pathology and microscopy findings.

RESULTS

Both contrast agents allowed precise determination of lesion diameters with an average accuracy of 6.8%+/-1.3%. Rim enhancement during dynamic MRI was superior for Gd-DTPA (P<0.001) and revealed slightly higher lesion diameters compared to the results of follow-up MR studies. A persistent enhancement of necrotic liver and muscle tissue was observed for both contrast agents throughout the observation period, suggesting that simple diffusion-type processes may underlie the supposed affinity of Bis-Gd-MP for tissue necrosis.

CONCLUSION

Bis-Gd-MP and Gd-DTPA are equally well suited for postinterventional lesion assessment in LITT.

Cell tracking with gadophrin-2: a bifunctional contrast agent for MR imaging, optical imaging, and fluorescence microscopy

The purpose of this study was to assess the feasibility of use of gadophrin-2 to trace intravenously injected human hematopoietic cells in athymic mice, employing magnetic resonance (MR) imaging, optical imaging (OI), and fluorescence microscopy. Mononuclear peripheral blood cells from GCSF-primed patients were labeled with gadophrin-2 (Schering AG, Berlin, Germany), a paramagnetic and fluorescent metalloporphyrin, using established transfection techniques with cationic liposomes. The labeled cells were evaluated in vitro with electron microscopy and inductively coupled plasma atomic emission spectrometry. Then, 1x10(6)-3x10(8) labeled cells were injected into 14 nude Balb/c mice and the in vivo cell distribution was evaluated with MR imaging and OI before and 4, 24, and 48 h after intravenous injection (p.i.). Five additional mice served as controls: three mice were untreated controls and two mice were investigated after injection of unlabeled cells. The contrast agent effect was determined quantitatively for MR imaging by calculating signal-to-noise-ratio (SNR) data. After completion of in vivo imaging studies, fluorescence microscopy of excised organs was performed. Intracellular cytoplasmatic uptake of gadophrin-2 was confirmed by electron microscopy. Spectrometry determined an uptake of 31.56 nmol Gd per 10(6) cells. After intravenous injection, the distribution of gadophrin-2 labeled cells in nude mice could be visualized by MR, OI, and fluorescence microscopy. At 4 h p.i., the transplanted cells mainly distributed to lung, liver, and spleen, and 24 h p.i. they also distributed to the bone marrow. Fluorescence microscopy confirmed the distribution of gadophrin-2 labeled cells to these target organs. Gadophrin-2 is suited as a bifunctional contrast agent for MR imaging, OI, and fluorescence microscopy and may be used to combine the advantages of each individual imaging modality for in vivo tracking of intravenously injected hematopoietic cells.

Tumor enhancement using Mn-metalloporphyrin in mice: Magnetic resonance imaging and histopathologic correlation

PURPOSE

To determine the signal enhancement characteristics of tumors after administration of a metalloporphyrin derivative, HOP-9P (13, 17-bis (1-carboxypropionyl) carbamoylethyl-3, 8-bis (1-phenylpropyloxyethyl)-2, 7, 12, 18-tetramethyl-porphyrinato manganese (III)) and to determine whether HOP-9P is tumor-necrosis specific.

MATERIALS AND METHODS

Ten C3H/He mice bearing a SCC VII tumor in the right flank were examined using T1-weighted conventional spin echo magnetic resonance (MR) imaging before contrast injection, and five minutes, one hour, and 24 hours after intravenous administration of 0.1 mmol/kg of HOP-9P. Following the imaging schedule, the mice were sacrificed, and sectioned in the same axial planes as the MR images. Based on an MR imaging-histopathologic correlation, mean signal intensities were measured, and signal-to-noise ratios (SNR) were calculated for both pure viable component and admixture of necrotic and viable component of the tumor.

RESULTS

Mean SNR of the pure viable component peaked at one hour (35.0 +/- 3.8) and maintained that level until 24 hours (34.6 +/- 3.6). Mean SNR of the admixture of necrotic and viable component peaked at 24 hours (44.3 +/- 12.1).

CONCLUSION

Although different enhancement patterns were seen between the pure viable component and the admixture of necrotic and viable component, HOP-9P enhanced both of the two components.

Detection and quantification of breast tumor necrosis with MR imaging: value of the necrosis-avid contrast agent Gadophrin-3

RATIONALE AND OBJECTIVES

The authors evaluated the use of T1-weighted magnetic resonance (MR) imaging with Gadophrin-3 enhancement and of plain T2-weighted MR imaging to detect and quantify breast tumor necrosis.

MATERIALS AND METHODS

Twenty EMT-6 tumors (mouse mammary sarcoma), implanted into the mammary fat pad of BALB/c-AnNCrl mice, underwent MR imaging with plain T2-weighted and T1-weighted fast field echo sequences before and 24 hours after injection of Gadophrin-3, a new necrosis-avid contrast agent. Tumor necrosis on MR images was quantified by means of a dedicated segmentation program and was correlated with histologic findings.

RESULTS

In all tumors a central necrosis was revealed by histopathologic analysis, and central enhancement was seen with Gadophrin-3 on T1-weighted images. Small tumors (diameter, < 1 cm) showed an inhomogeneous central enhancement, whereas larger tumors (diameter, > 1 cm) enhanced mainly in the periphery of necrotic tissue. Plain T2-weighted images showed a hyperintense central area in only three of 20 cases with a large central necrosis.

CONCLUSION

Gadophrin-3-enhanced T1-weighted images are superior to plain T2-weighted images for the detection of necrosis in a murine tumor xenograft model.

Dynamic enhancement features of gadophrin-2 on magnetic resonance imaging: an experimental model of VX2 carcinoma and bacterial abscess in rabbit thigh

RATIONALE AND OBJECTIVES

To determine the dynamic enhancement features of malignant tumor and bacterial abscess in rabbits on magnetic resonance imaging (MRI) after injection of gadolinium mesoporphyrin (gadophrin-2) and to correlate them with histopathologic findings.

METHODS

Six VX2 carcinomas and six bacterial abscesses were experimentally induced in either thigh of six rabbits. Dynamic T1-weighted MRI was performed before and 1, 3, 5, 10, 30 minutes and 16, 21, 72 hours after intravenous injection of gadophrin-2 (0.05 mmol/kg). The enhancement ratios of lesions were calculated for each time point. All tumors and abscesses were sectioned along the same plane of MR images for a detailed MRI-histopathologic correlation.

RESULTS

In tumors and abscesses, peripheral-rim enhancement appeared on MRI at 1, 3, 5, 10, 30 minutes after injection of gadophrin-2. The lesions showed peripheral enhancement with irregular central enhancement or diffuse enhancement after 16 and 21 hours, and there was diffuse enhancement of the entire lesion after 72 hours. Enhancement ratios in tumor-necrosis mixed area and the pure necrotic area in VX2 carcinoma and the central cavity in bacterial abscess were significantly lower than that in the compact cellular portion in VX2 carcinoma and the wall of abscess at early phase (P < 0.01). On delayed phase MRI, there was no statistical significance in enhancement ratio of three histologic parts of VX2 carcinoma (P > 0.05) and two histologic parts of abscess (P > 0.05). Rapid enhancement at early phase with diminishing signal intensity at delayed phase is indicative of viable compact tumor and delayed strong enhancement is indicative of necrosis.

CONCLUSION

It is difficult to distinguish an abscess from a tumor on gadophrin-2 enhanced MRI especially when intratumoral necrosis is prominent. However, the trend and degree of enhancement by gadophrin-2 could be helpful in discrimination between viable tumor and tumor necrosis.

Evaluation of the microangioarchitecture of tumors by use of monochromatic x-rays

RATIONALE AND OBJECTIVES

The purpose was to compare differences in the depiction of small vessels in tumors seen on microangiograms from a conventional soft x-ray system with those from a synchrotron radiation system and to evaluate the microangioarchitecture of these tumors and the growth of neovascularization.

METHODS

VX2 carcinomas transplanted to the auricles of 15 rabbits randomized into three groups were investigated after 1, 3, and 7 days. Five normal rabbits were the controls. Barium sulfate, to which sufficient gelatin had been added, was injected into the auricular artery. Microangiograms of auricle specimens were obtained with both a conventional soft x-ray system and a synchrotron radiation system.

RESULTS

The conventional x-ray system could detect vessels with diameters of approximately 100 microm, whereas the monochromatic synchrotron radiation system could detect small vessels with diameters of less than 25 microm. On day 1, there was moderate vascularization and flexure vessels were present in the transplantation area. On day 3, dilated vessels were present in the peripheral areas of the tumors and tortuous vessels in the central areas. On day 7, hypovascular areas had increased in the central area.

CONCLUSIONS

The synchrotron radiation system confirmed the growth of neovascularization in the tumors. This system should provide a useful tool for evaluating the microangioarchitecture of tumors.