Perfusion CT of the brain in the assessment of flow alterations during brachytherapy of meningioma.

PURPOSE: The aim was to investigate the use of perfusion CT of the brain in the assessment of flow alterations during brachytherapy of meningiomas. MATERIAL AND METHODS: Six patients with an intracranial meningioma were investigated during brachytherapy treatment by stereotactic implantation of I-125 seeds. Cerebral blood flow (CBF) in the tumour centre and the tumour periphery as well as in the normal brain parenchyma was determined by perfusion CT. Follow-up examinations were performed during the first year after the implantation. The CBF of the normal brain parenchyma was used as control. RESULTS: In the beginning of therapy, the mean+/-SEM blood flow in the tumour centre was 231.4+/-58.1 ml/100 g/min and in the periphery 223.5+/-53.8 ml/100 g/min. Within three months after the iodine seed implantation, the tumour blood flow had decreased 41%. At the one-year follow-up, the tumour blood flow in the centre had decreased to 68.7+/-45.9 ml/100 g/min. In the periphery of the tumour, it remained nearly unchanged (199.3+/-101.0 ml/100 g/min). The CBF values obtained from normal brain parenchyma did not decrease during the treatment. Throughout the study, the mean CBF for the normal grey matter was 38.5+/-2.9 ml/100 g/min, and 22.3+/-1.2 ml/100 g/min for the normal white matter. CONCLUSION: Perfusion CT seems to enable accurate monitoring of the blood flow of meningiomas during brachytherapy, and could be used in clinical situations where blood flow changes in brain and tumours should be investigated.

Spin lock and magnetization transfer MR imaging of local liver lesions.

The present study was designed to evaluate tissue contrast characteristics obtained with the spin-lock (SL) technique by comparing the results with those generated with a magnetization transfer(MT)-weighted gradient echo [GRE, echo-time (TE)=40 ms] sequence. Twenty-eight patients with hepatic hemangiomas (n=14), or metastatic liver lesions (n=14) were imaged at 0.1 T by using identical imaging parameters. Gradient echo, single-slice off-resonance MT, and multiple-slice SL sequences were obtained. SL and MT-effects were measured from the focal liver lesions and from normal liver parenchyma. In addition, tissue contrast values for the liver lesions were determined. Statistically significant difference between the SL-effects of the hemangiomas and metastases, and also between the MT-effects of the lesions was observed (p < 0.02). Tissue contrast values for the lesions proved to be quite similar between the SL and MT techniques. Our results indicate that at 0.1 T multiple-slice SL imaging provides MT based tissue contrast characteristics in tissues rich in protein with good imaging efficiency and wide anatomical coverage, and with reduced motion and susceptibility artifacts.

Determination of T1rho values for head and neck tissues at 0.1 T: a comparison to T1 and T2 relaxation times.

In order to optimize head and neck magnetic resonance (MR) imaging with the spin-lock (SL) technique, the T1rho relaxation times for normal tissues were determined. Furthermore, T1rho was compared to T1 and T2 relaxation times. Ten healthy volunteers were studied with a 0.1 T clinical MR imager. T1rho values were determined by first measuring the tissue signal intensities with different locking pulse durations (TL), and then by fitting the signal intensity values to the equation with the least-squares method. The T1rho relaxation times were shortest for the muscle and tongue, intermediate for lymphatic and parotid gland tissue and longest for fat. T1rho demonstrated statistically significant differences (p < 0.05) between all tissues, except between muscle and tongue. T1rho values measured at locking field strength (B1L) of 35 microT were close to T2 values, the only exception being fat tissue, which showed T1rho values much longer than T2 values. Determination of tissue relaxation times may be utilized to optimize image contrast, and also to achieve better tissue discrimination potential, by choosing appropriate imaging parameters for the head and neck spin-lock sequences.

MnDPDP as a negative hepatic contrast agent: evaluation of STIR imaging compared with T1-weighted SE and GE techniques.

Our goal was to assess the utility of manganese dipyridoxyl diphosphate (MnDPDP) as a negative hepatic contrast agent in short inversion time IR MRI (STIR). Twenty patients with focal liver lesions (15 with metastatic disease, 5 with hemangiomas) underwent MRI (T1-weighted SE, breath-hold GE, and STIR sequences) before and after infusion of MnDPDP (5 mumol/kg). We then compared the results obtained with each sequence for hepatic parenchymal enhancement, lesion-to-liver contrast-to-noise ratio (C/N) measurements, and the number of focal liver lesions observed in pre- and postcontrast images. Hepatic enhancement values of 25.3 +/- 9.7 and 33.6 +/- 2.7% (mean +/- SEM) were obtained for the T1-weighted SE and GE sequences, respectively. The STIR sequence showed 78.9 +/- 2.1% negative enhancement (decrease of parenchymal signal intensity). Although a significant (p < 0.0001) C/N increase was seen after MnDPDP administration for all sequences, STIR showed the highest increase (149.0 +/- 25.5%) compared with T1-weighted SE (58.5 +/- 12.7%) and GE (83.3 +/- 7.2%) sequences. Similarly, more lesions for all sequences were detected, but again STIR showed the greatest postcontrast increase (29.0%). MnDPDP is an effective hepatic contrast agent. As both the negative hepatic enhancement and the increase in lesion-to-liver C/N were superior with the STIR sequence when compared with the positive enhancement and C/N values produced by the T1-weighted sequences, it should be considered for inclusion in the imaging protocol for patients with focal liver disease.

Functional CT with an experimental intravascular contrast agent in the assessment of liver vascular physiology.

RATIONALE AND OBJECTIVES: We evaluated liver vascular physiology with a functional spiral computed tomography (CT) technique and an intravascular contrast agent. METHODS: Eleven rabbits were studied by means of continuous 40-second single-section data acquisition after bolus injection of an experimental contrast agent. Sequential images were reconstructed at 200-msec intervals. Aortic, portal and hepatic venous, and liver time-HU curves were obtained. From these, hepatic blood volume and flow, tissue transit times, and arterial and portal contributions to total liver blood supply were assessed. RESULTS: The following measures were obtained: hepatic blood volume fraction, 0.33 +/- 0.03 (mean +/- standard error); total flow, 241.1 mL/min +/- 33.6 per 100 g of tissue (arterial component, 11.3 mL/min +/- 3.0 per 100 g of tissue; portal component, 226.4 mL/min +/- 30.7 per 100 g of tissue); arterial transit time, 8.7 seconds +/- 1.6; portal transit time, 8.7 seconds +/- 1.3; arterial to portal perfusion ratio, 0.06 +/- 0.01; and calculated arterial and portal perfusion indexes, 0.05 +/- 0.01 and 0.95 +/- 0.01, respectively. CONCLUSION: Functional CT is a promising, high-resolution tomographic imaging technique for evaluating liver perfusion.

Basic principles of MR contrast agents.

Although familiar for CNS enhancement, contrast agents for body MR applications are both similar and different. This short summary emphasizes the basics of tissue relaxation and the added influences of paramagnetic or superparamagnetic pharmaceuticals. An overview of safety and cost considerations is included.

Spin lock magnetic resonance imaging in the differentiation of hepatic haemangiomas and metastases.

Spin lock (SL) imaging technique, generating T1 rho-weighted images, was applied to the differentiation of hepatic haemangiomas from metastatic focal liver lesions. 17 haemangiomas and 16 metastases in 32 patients were imaged at the field-strength of 0.1 T using a multiple slice SL technique and a conventional gradient-echo (GRE) sequence with identical timing parametres. Spin lock effects of the hepatic lesions and different abdominal tissues were calculated. Images with adequate coverage of the liver and of good quality with few motion induced artefacts were acquired. A definite, statistically significant, difference was found between the SL-effects of hepatic haemangiomas and a liver metastases. Haemangiomas showed an SL effect of 46.6 +/- 3.4% and metastases of 56.2 +/- 5.8% (mean +/- SD, p < 0.0001). The multiple slice SL technique showed potential in distinguishing haemangiomas from metastatic liver lesions and should be considered as an alternative to the conventional T2 and magnetization transfer (MT) based methods.

Detection of focal liver lesions with superparamagnetic iron oxide: value of STIR and SE imaging.

OBJECTIVE: We assessed the value of superparamagnetic iron oxide (SPIO) particles on the detection of focal liver lesions by MRI. MATERIALS AND METHODS: Twenty patients with one to five focal liver lesions, primarily detected with ultrasonography and/or contrast-enhanced CT, were evaluated further with unenhanced and iron oxide-enhanced MRI at 1.0 T. Superparamagnetic iron oxide particles were administered intravenously as a slow infusion. Then T1-, T2-, and proton density-weighted SE images were obtained. In addition, the performance of a short TI inversion recovery (STIR) sequence was evaluated. RESULTS: The iron oxide contrast medium had marked effects on liver signal-to-noise (S/N) and tumor-to-liver contrast-to-noise (C/N) ratios but only minimal effects on tumor S/N ratios in cases of malignant tumor foci. Lesion-to-liver contrast, expressed as differences between the tumor and liver S/N ratios, improved very significantly after SPIO infusion with all four pulse sequences. Contrast enhancement of the liver parenchyma was best in T2-weighted SE images, but the tumor-to-liver C/N values were highest with the postcontrast STIR sequence. The SPIO enhancement revealed a number of additional focal lesions (31%), also foci under 1 cm in diameter. In three benign focal lesions, SPIO infusion produced a definite reduction in the S/N ratio of the lesions in contrast to the minimal change measured in malignant foci. The favorable performance of the STIR sequence contradicts the disappointing results previously obtained at 0.6 T. CONCLUSION: Superparamagnetic iron oxide is a promising new contrast medium for MR examinations of the liver, increasing the conspicuity and reducing the detectability threshold of focal hepatic lesions.