[A pharmacokinetic analysis of Gd-DTPA enhancement in MRT in breast carcinoma]

Neoadjuvante Chemotherapie des Mammakarzinoms

PURPOSE

The aim of this study was to evaluate whether quantitative changes in contrast enhancement (CE) after neoadjuvant chemotherapy (NC) are associated with histological signs of tumor regression and whether quantitative dynamic MRI (dMRI) is capable of accurately assessing preoperative tumor size compared to mammography (MG) and ultrasound (US).

METHODS

Thirty-one patients with breast cancer underwent MRI before and after NC. Dynamic CE was measured using a turbo-FLASH sequence and quantified by a two-compartment model, where two parameters, k(ep) (distribution constant rate) and A (amplitude), were calculated and color mapped.

RESULTS

When tumors had signs of histological regression in the operative specimen (n=17) decrease of the parameters A and k(ep) was significantly more marked compared to tumors without regression (n=12). The correlation between tumor size measured by dMRI and histopathology was 0.81 when areas of unspecific CE were included; when they were not included the correlation was 0.66 and tumor size was systematically underestimated. In 26 patients dMRI was retrospectively compared with MG (r=0.51; dMRI, r=0.80) and in 22 patients with US (r=0.60; dMRI, r=0.75).

CONCLUSION

Changes in dynamic CE are associated with histological tumor regression. Quantitative dMRI enables a valid assessment of tumor residue and is superior to MG and US. Remaining unspecific CE within the original tumor site should be considered as potentially malignant.

[Breast cancer. Sonography and magnetic resonance mammography]

Breast cancer is the most common malignant tumor in women: Almost 10% will suffer from breast cancer during their life; almost half of these will die of it. The spectrum of radiologic methods for diagnosing breast cancer is wide, including X-ray mammography, ultrasound, magnetic resonance mammography, and minimally invasive biopsies. This second part of two covers ultrasound of the breast and magnetic resonance mammography.

Contrast-enhanced high in-plane resolution dynamic MRI of the breast. Are there advantages in comparison to standard dynamic MRI?

OBJECTIVE

To evaluate the diagnostic advantages of high in-plane resolution contrast-enhanced (CE) magnetic resonance imaging (MRI) of the breast in comparison to standard CE-MRI.

METHODS

Forty-one patients with 51 hypervascularized lesions were selected prospectively after undergoing bilateral standard CE MRI (slice thickness 4 mm, in-plane resolution 1.52 x 1.25 mm2, temporal resolution 81 s). Patients underwent high in-plane resolution CE MRI, either (n=21) a two-dimensional fast-low-angle-shot sequence (slice thickness 4 mm, in-plane resolution 0.76 x 0.63 mm2, temporal resolution 96 s) or (n=20) a SE sequence being used (slice thickness 4 mm, in-plane resolution 0.8 x 0.63 mm2, temporal resolution 115 s).

RESULTS

Histopathology revealed 33 malignant and 18 benign lesions (0.2-2.2 cm). Morphologic characteristics were much better visualized with high in-plane resolution. Additional diagnostic information, however, resulted only in one patient with fibroadenoma due to a better visualization of smooth contours.

CONCLUSIONS

High in-plane resolution provides better visualization of morphologic patterns in comparison to standard dynamic MRI. However, a diagnostic advantage is only rare.

Rationale for a national multi-centre study of magnetic resonance imaging screening in women at genetic risk of breast cancer

In 1994, the UK National Health Service identified as a research priority that magnetic resonance imaging (MRI) should be assessed as a screening tool for young, pre-menopausal women who are at a high genetic risk of developing breast cancer. In 1997 a national multicentre study was established to compare MRI with X-ray mammography as a method for screening for breast cancer in this group of women. This paper reviews the relevant literature and describes the rationale that led to the setting up of this study.

Diagnostic potential of ultrafast contrast-enhanced MRI of the breast in hypervascularized lesions: are there advantages in comparison with standard dynamic MRI?

PURPOSE

Our goal was to evaluate possible diagnostic advantages of ultrafast MRI of the breast in comparison with dynamic MRI.

METHOD

Thirty patients with 35 hypervascularized lesions were selected prospectively after undergoing standard dynamic MRI (temporal resolution 87 s). Patients underwent additional ultrafast imaging (temporal resolution 2 s). Onset, rate, and pattern of enhancement were analyzed.

RESULTS

Histopathology revealed 15 malignant and 20 benign lesions (3-40 mm). Enhancement pattern was centripetal in 2 benign and 4 malignant lesions, centrifugal in 5 and 3, and homogeneous in 13 and 8. The onset of lesion enhancement ranged from 3 to 13 s (parenchymal enhancement 4-14 s) and the rate of enhancement from 3 to 70%/s, both without any correlation to the histologic diagnosis. There was no significant difference between ultrafast and standard dynamic MRI.

CONCLUSION

Ultrafast MRI does not provide additional information in comparison with standard dynamic MRI.

Pharmacokinetic analysis of Gd-DTPA enhancement in dynamic three-dimensional MRI of breast lesions

The purpose of this study was to demonstrate that dynamic MRI covering both breasts can provide sensitivity for tumor detection as well as specificity and sensitivity for differentiation of tumor malignancy. Three-dimensional gradient echo scans were used covering both breasts. Before Gd-DTPA bolus injection, two scans were obtained with different flip angles, and after injection, a dynamic series followed. Thirty-two patients were scanned according to this protocol. From these scans. In addition to enhancement, the value of T1 before injection was obtained. This was used to estimate the concentration of Gd-DTPA as well as the pharmacokinetic parameters governing its time course. Signal enhancement in three-dimensional dynamic scanning was shown to be a sensitive basis for detection of tumors. In our series, all but two mammographically suspicious lesions did enhance, and in three cases, additional enhancing lesions were found, two of which were in the contralateral breast. The parameter most suited for classification of breast lesions into benign or malignant was shown to be the pharmacokinetically defined permeability k31, which, for that test, gave a sensitivity of 92% and a specificity of 70%. Our three-dimensional dynamic MRI data are sensitive for detection of mammographically occult breast tumors and specific for classification of these as benign or malignant.

Probing tumor microvascularity by measurement, analysis and display of contrast agent uptake kinetics

This paper describes a measurement protocol for acquiring quantitative dynamic MRI data and novel analysis and display software (Magnetic Resonance Imaging Workbench (MRIW)). Proton density-weighted and T1-weighted two-dimensional gradient echo images are used to quantify tissue contrast agent concentration. The dynamic studies last approximately 7 minutes, with 10-second temporal resolution. Analyses of signal and concentration changes with time are performed, allowing capillary permeability-surface area product, tissue leakage space, enhancement onset time, mean enhancement gradient and maximum enhancement level to be mapped as false-color parametric overlays registered with anatomic images. Quantification of permeability and leakage space provides a method for comparing physiology in patients between visits or for intersite comparisons.

Dynamic 3D-MR mammography: is there a benefit of sophisticated evaluation of enhancement curves for clinical routine?

The purpose of the study was to compare standard analysis with pharmacokinetic analysis of time-intensity curves in dynamic three-dimensional (3D) MR mammography (MRM) for their capability of differentiating benign from malignant disease. Dynamic MRM of the whole breast was performed at 1.0 T using an axial fast low-angle shot (FLASH) 3D sequence. For the standard evaluation, the enhancement of the first minute (E1) and the slope of enhancement from minute 2 to 10 (SE2-10) were calculated. For pharmacokinetic analysis, the amplitude of enhancement (A), distribution time (t21), and elimination time (tel) were computed. Sixty-two histologically verified lesions were evaluated. The standard evaluation methods yielded a highly significant difference between benign and malignant disease for E1 (P = .0008) and SE2-10 (P = .0001). The pharmacokinetic parameters gained similarly significant P values (A, P = .0014; t21, P = .0024; tel, P = .0001). Both standard and pharmacokinetic analysis concordantly discriminated between benign and malignant lesions in discriminant analysis. Compared with standard analysis, a pharmacokinetic analysis of time-intensity curves is not beneficial for routine clinical diagnosis.

Pharmacokinetic mapping of the breast: a new method for dynamic MR mammography

A dynamic contrast-enhanced MRI technique for whole breast examinations is presented. The fast kinetics of tissue response during and after constant-rate intravenous infusion of gadolinium diethylenetriaminopentaacetic acid was resolved using a strongly T1-weighted saturation recovery TurboFLASH sequence that makes it possible to acquire signal-time courses sequentially from 15 adjacent slices with a temporal sampling rate of 21 s. On the basis of the mathematically established and experimentally verified linear relationship between the measured saturation recovery TurboFLASH signal variation and the gadolinium diethylenetriaminopentaacetic acid concentration in the tissue, the signal-time courses were analyzed within the framework of pharmacokinetic modeling. In our study, the tissue response was parameterized adequately using an open linear two-compartment model. With this approach, the tissue specific information contained in the signal-time course can be described using only two parameters: an amplitude A, reflecting the degree of MR signal enhancement, and an exchange parameter k21, characterizing vascular permeability and perfusion of the tissue. A clearly arranged representation of the large amount of data (480 saturation recovery TurboFLASH breast images/examination) was accomplished by means of color coding of the computed parameters, resulting in one color-coded pharmacokinetic parameter map/cross-section.