Thomas G. Maris

Assessment of liver iron overload by T2-Quantitative magnetic resonance imaging: Correlation of T2-QMRI measurements with serum ferritin concentration and histologic grading of siderosis

PURPOSE To correlate hepatic 1/T2 values obtained by means of a T2-Quantitative MRI (T2-QMRI) technique with three widely applied methods for the evaluation of hemosiderosis, i.e., (a) liver iron concentrations (LFeC) (b) serum ferritin (SF), and (c) histologic grading of siderosis. The impact of coexisting hepatitis was also considered. T2-QMRI measurements were compared with signal intensity (SI) ratio measurements on conventional SE images. MATERIALS AND METHODS Liver T2 relaxation times were calculated in 40 thalassemic patients, on a 0.5 T magnetic resonance imaging system using a multiple spin-echo sequence with parameters: TR = 2500 ms, TE = 12 ms in 20 symmetrically repeatable echoes. RESULTS (a) 1/T2 values were well correlated (r = 0.97) with liver iron concentrations, which ranged from 2.32 to 18.0 mg/g dry weight (normal < 1.6 mg/g). (b) 1/T2 values were also correlated with serum ferritin levels (r = 0.84). At various 1/T2 values, serum ferritin levels were higher for the anti-HCV(+) patients than the anti-HCV(-) ones. (c) T2 values corresponding to successive grades of siderosis presented statistically significant differences. (d) SI ratio measurement assigned less statistically significant results, as compared to T2 values. CONCLUSION T2-QMRI measurement of T2 relaxation time is more accurate than SI ratios in evaluating liver iron overload. It is particularly useful for hemosiderotic patients with coexisting hepatitis since, in this case, serum ferritin is not considered a reliable index of hemosiderosis.

An update on the assessment of osteoporosis using radiologic techniques

In this article, the currently available radiologic techniques for assessing osteoporosis are reviewed. Density measurements of the skeleton using dual X-ray absorptiometry (DXA) are clinically indicated for the assessment of osteoporosis and for the evaluation of therapies. DXA is the most widely used technique for identifying patients with osteoporosis. Quantitative computed tomography (QCT) is the only method, which provides a volumetric density. Unlike DXA, QCT allows for selective trabecular measurement and is less sensitive to degenerative diseases of the spine. The analysis of bone structure in conjunction with bone density is an exciting new field in the assessment of osteoporosis. High-resolution multi-slice CT and micro-CT are useful tools for the assessment of bone microarchitecture. A growing literature indicates that quantitative ultrasound (QUS) techniques are capable of assessing fracture risk. Although the ease of use and the absence of ionizing radiation make QUS attractive, the specific role of QUS techniques in clinical practice needs further determination. Considerable progress has been made in the development of MR techniques for assessing osteoporosis during the last few years. In addition to relaxometry techniques, high-resolution MR imaging, diffusion MR imaging and in-vivo MR spectroscopy may be used to quantify trabecular bone architecture and mineral composition.

MR imaging of the small bowel with a true-FISP sequence after enteroclysis with water solution.

Gourtsoyiannis N, Papanikolaou N, Grammatikakis J, et al. MR imaging of the small bowel with a true-FISP sequence after enteroclysis with water solution. Invest Radiol 2000;35:707–711. RATIONALE AND OBJECTIVES.To evaluate a novel MR enteroclysis technique for small-bowel imaging. METHODS.Twenty-one patients with suspected small-bowel disease underwent both MR and conventional enteroclysis. MR enteroclysis was performed by injecting an iso-osmotic water solution through a nasojejunal catheter with a flow rate of 80 to 150 mL/min. A maximum of 2 L of water solution was administered. A dynamic heavily T2-weighted single-shot turbo spin-echo sequence was applied in coronal orientation to monitor the bowel filling and adequate distention. Twelve 4-mm-thick slices were acquired by using a true fast imaging with steady-state precession (true-FISP) sequence during an 18-second breath-hold interval. Small-bowel distention, wall conspicuity, homogeneity of opacification, and the presence of artifacts were subjectively evaluated by two reviewers using five-point scales. RESULTS.Chemical shift artifacts were low and ghost artifacts were absent. Susceptibility artifacts were more prominent in the ileum; motion artifacts were low in the jejunum, ileum, and ileocecal area. Homogeneity of opacification was very good in the jejunum, good to very good in the ileum, and good in the ileocecal area. Distention was very good to excellent in the jejunum and ileum and very good in the ileocecal area. Wall conspicuity was very good to excellent in the jejunum and ileum. CONCLUSIONS.MR enteroclysis with the true-FISP sequence produced high-quality images of the small bowel. Further clinical studies are required to determine the clinical efficacy of the new technique compared with conventional enteroclysis.

Small SRS photon field profile dosimetry performed using a PinPoint air ion chamber, a diamond detector, a novel silicon-diode array "DOSI…, and polymer gel dosimetry. Analysis and intercomparison

Small photon fields are increasingly used in modern radiotherapy and especially in IMRT and SRS/SRT treatments. The uncertainties related to small field profile measurements can introduce significant systematic errors to the overall treatment process. These measurements are challenging mainly due to the absence of charged particle equilibrium conditions, detector size and composition effects, and positioning problems. In this work four different dosimetric methods have been used to measure the profiles of three small 6 MV circular fields having diameters of 7.5, 15.0, and 30.0 mm: a small sensitive volume air ion chamber, a diamond detector, a novel silicon-diode array (DOSI), and vinyl-pyrrolidone based polymer gel dosimeter. The results of this work support the validity of previous findings, suggesting that (a) air ion chambers are not suitable for small field dosimetry since they result in penumbra broadening and require significant corrections due to severe charged particle transport alterations; (b) diamond detectors provide high resolution and rather accurate small field profile measurements, as long as positioning problems can be addressed and the necessary dose rate corrections are correctly applied; and (c) the novel silicon-diode array (DOSI) used in this study seems to be adequate for small field profile measurements overcoming positioning problems. Polymer gel data were assumed as reference data to which the other measurement data were compared both qualitatively and quantitatively using the gamma-index concept. Polymer gels are both phantom and dosimeter, hence there are no beam perturbation effects. In addition, polymer gels are tissue equivalent and can provide high-spatial density and high-spatial resolution measurements without positioning problems, which makes them useful for small field dosimetry measurements. This work emphasizes the need to perform beam profile measurements of small fields (for acceptance, commissioning, treatment planning systems data feed, and periodic quality assurance purposes) using more than one dosimetric method. The authors believe this to be a safe way towards the reduction of the overall uncertainty related to SRS/SRT treatments.

Comparison of two volumetric techniques for estimating liver volume using magnetic resonance imaging

To compare the conventional technique of manual planimetry with the point counting technique for estimating liver volume from magnetic resonance imaging (MRI) data.

MR cholangiopancreatography before and after oral blueberry juice administration.

Blueberry juice was used in 37 patients who underwent MR cholangiopancreatography (MRCP) examination. Quantitative and qualitative comparison between pre- and post-blueberry juice oral administration was made. Common bile duct and main pancreatic duct depiction improved statistically significantly (p < 0.05) after blueberry juice administration. Blueberry juice may be used routinely in MRCP studies as a natural, safe, and inexpensive negative contrast agent with high efficacy.

The pancreas in β-thalassemia major: MR imaging features and correlation with iron stores and glucose disturbunces

The study aims at describing the MR features of pancreas in beta-thalassemia major, investigating the relations between MR findings and glucose disturbances and between hepatic and pancreatic siderosis. Signal intensity ratios of the pancreas and liver to right paraspinous muscle (P/M, L/M) were retrospectively assessed on abdominal MR imaging studies of 31 transfusion-dependent patients with beta-thalassemia major undergoing quantification of hepatic siderosis and 10 healthy controls, using T1- (120/4/90), intermediate in and out of phase - (120/2.7, 4/20), and T2*-(120/15/20) weighted GRE sequences. Using the signal drop of the liver and pancreas on opposed phase images, we recorded serum ferritin and results of oral glucose tolerance test (OGTT). Decreased L/M and P/M on at least the T2* sequence were noticed in 31/31 and 30/31 patients, respectively, but no correlation between P/M and L/M was found. Patients with pathologic OGTT displayed a higher degree of hepatic siderosis (p < 0.04) and signal drop of pancreas on opposed phase imaging (p < 0.025), implying fatty replacement of pancreas. P/M was neither correlated with glucose disturbances nor serum ferritin. Iron deposition in the pancreas cannot be predicted by the degree of hepatic siderosis in beta-thalassemia major. Fatty replacement of the pancreas is common and may be associated with glucose disturbances.

Narrow stereotactic beam profile measurements using N-vinylpyrrolidone based polymer gels and magnetic resonance imaging

In this work, polymer gel-MRI dosimetry (using VIPAR gels), radiographic film and a PinPoint ion chamber were used for profile measurements of 6 MV x-ray stereotactic beams of 5 and 10 mm diameter. The VIPAR gel-MRI method exhibited a linear dose response up to 32 Gy. VIPAR gels were found to resolve the penumbra region quite accurately, provided that the in-plane image resolution of the related T2-map is adequate (< or = 0.53 mm). T2-map slice thickness had no significant effect on beam profile data. VIPAR measurements performed with a spatial resolution of 0.13 mm provided penumbra widths (80%-20% distance) of 1.34 and 1.70 mm for the 5 and 10 mm cones respectively. These widths were found to be significantly smaller than those obtained with the film (2.23 mm for the 5 mm cone, 2.45 mm for the 10 mm cone) and PinPoint (2.25 mm for the 5 mm cone, 2.52 mm for the 10 mm cone) methods. Regarding relative depth dose measurements, good correlation between VIPAR gel and PinPoint data was observed. In conclusion, polymer gel-MRI dosimetry can provide relatively accurate profile data for very small beams used in stereotactic radiosurgery since it can overcome, to some extent, the problems related to the finite size of conventional detectors.

Comparison between two-point and four-point methods for quantification of apparent diffusion coefficient of normal liver parenchyma and focal lesions. Value of normalization with spleen

PURPOSE To compare two quantification techniques of apparent diffusion coefficient (ADC), both in normal liver parenchyma and focal lesions, and to investigate any potential value of normalization. MATERIALS AND METHODS Fifty-six consecutive patients underwent MRI examination of the liver, including a single shot spin-echo echo planar imaging diffusion sequence with four b-values (0, 50, 500 and 1000s/mm(2)). ADC maps were reconstructed based on a two-point method (b-values: 500 and 1000s/mm(2)) and a four-point method (b-values: 0, 50, 500 and 1000s/mm(2)). Comparison of absolute ADC measurements of the liver, benign and malignant focal lesions was performed between the two- and four-point techniques. The same analysis was done on normalized ADC values (absolute ADC values divided by spleen ADC values). RESULTS The difference between mean two-point and four-point ADC values of normal liver (absolute: 1.237x10(-3), 1.615x10(-3)mm(2)/s, normalized: 1.40, 1.52, respectively) was statistically significant (p<0.0001 and p=0.0061). Significantly higher absolute ADC values of benign and malignant lesions were recorded with the four-point method (2.860x10(-3) and 1.307x10(-3)mm(2)/s) over the two-point method (2.243x10(-3), and 1.011x10(-3)mm(2)/s) (p<0.0001 in both) while the same differences in normalized values were proven statistically non-significant for benign lesions (p=0.788) and statistically significant for malignant lesions (p=0.015). Both differences in absolute and normalized ADC values of benign versus malignant lesions based on two- and four-point methods were found to be significant (p<0.0001). CONCLUSION ADC quantification of the liver may be performed with a two-point method (b-values of 500 and 1000s/mm(2)), while normalization of ADC measurements with the spleen is not further improving lesion characterization.

Quantification of liver iron overload by T2 quantitative magnetic resonance imaging in thalassemia: impact of chronic hepatitis C on measurements.

PURPOSE Measurement of liver T2 values seems to be an accurate and sensitive magnetic resonance imaging (MRI) method for the quantification of liver hemosiderosis in multiple transfused patients with thalassemia. Because many of these patients have coexistent chronic hepatitis C virus (HCV) infection, the effect of inflammatory changes on liver T2 values was assessed. MATERIALS AND METHODS Liver MRI studies of 35 HCV+ and 17 HCV- patients with beta-thalassemia, 9 HCV+ patients without thalassemia, and 10 healthy controls of the same age range (13 to 32 years) were reviewed. Iron status was assessed by serum ferritin in all patients, and determination of liver iron concentration (LIC) was available in 16 HCV+ patients with thalassemia. Histologic activity index (HAI) and grades of siderosis were evaluated in all HCV+ patients with thalassemia. RESULTS Patients with thalassemia had significantly lower T2 values (P < 0.0001) than subjects without thalassemia, whereas no difference existed between HCV+ patients without thalassemia and healthy controls. In HCV+ patients, LIC correlated more nearly with T2 values (r = 0.93) than with serum ferritin (r = 0.73). T2 values were not influenced by HAI score or fibrosis. CONCLUSION Liver T2 values were found to be more accurate than serum ferritin in predicting liver iron overload and were not influenced by the presence of chronic hepatitis C. Therefore, MRI could serve as a noninvasive alternative to liver biopsy for the quantification of hemosiderosis in HCV+ patients with thalassemia.