The German Thorotrast Cohort Study: a review and how to get access to the data

It is well known that exposures like those from (226)Ra, (224)Ra and Thorotrast(®) injections increase the risk of neoplasia in bone marrow and liver. The thorium-based radioactive contrast agent Thorotrast(®) was introduced in 1929 and applied worldwide until the 1950s, especially in angiography and arteriography. Due to the extremely long half-life of several hundred years and the life-long retention of the thorium dioxide particles in the human body, patients suffer lifetime internal exposure. The health effects from the incorporated thorium were investigated in a few cohort studies with a German study being the largest among them. This retrospective cohort study was set up in 1968 with a follow-up until 2004. The study comprises 2326 Thorotrast patients and 1890 patients of a matched control group. For those being alive at the start of the study in 1968 follow-up was done by clinical examinations on a biannual basis. For the others, causes of death were collected in various ways. Additionally, clinical, radiological and biophysical studies of patients were conducted and large efforts were made to best estimate the radiation doses associated with incorporation of the Thorotrast. The aim of this paper is to describe the cohort, important results and some open questions. The data from the German Thorotrast Study are available to other interested researchers. Information can be found at http://storedb.org .

[Therapy-induced effects in normal tissue]

More than 50% of cancer patients survive for more than 5 years, owing to modern and effective treatment. Therefore, long-term sequelae of treatment are more frequently seen than in the past. Such effects on normal tissue may both mimic and obscure tumor recurrences. Besides the direct consequences of surgery, tissue damage due to radiation or chemotherapy frequently cause problems in differential diagnosis. Among the numerous sequelae of radiotherapy, the most prominent are disturbance of the blood-brain barrier, radiation pneumonitis, osteodystrophy and osteoradionecrosis, fatty changes of bone marrow, or increased radiodensity of breast parenchyma. Chemotherapy may cause, e.g., diffuse abnormalities of white matter, pneumonitis and lung fibrosis, cardiomyopathy, or diffuse and patchy changes in bone marrow signals in MRI. The most devastating long-term complications are secondary cancers and leukemia induced by both radiotherapy and chemotherapy.

[Screening in cardiovascular diseases]

Cardiovascular disease still ranks number one in the mortality statistics in the industrialized world. In Germany the five most common causes of death are all associated with arteriosclerotic changes of the arterial vasculature. As the treatment often extends over long periods and it can be impossible for patients to work, peripheral arterial occlusive disease (PAOD) constitutes a not inconsiderable economic factor. Thus, screening for arteriosclerotic disease seems to be reasonable, because the potential for influencing arteriosclerotic changes is known to be higher in an early stage of the disease even before symptoms become apparent. Not every case can be cured, but progression can frequently be slowed down. The need for invasive procedures, some of them associated with ionizing radiation, limited the use of imaging of the arterial vasculature for a long time. Noninvasive clinical examinations such as the "ankle brachial index" (ABI) can indicate the presence of PAOD, though exact localization of the pathologic changes is not possible except with imaging methods. In contrast to these, MRI is a noninvasive imaging modality that does not involve ionizing radiation but offers high spatial resolution arterial imaging.

Cerebral arteriovenous malformations: morphologic evaluation by ultrashort 3D gadolinium-enhanced MR angiography

The purpose of this study was to evaluate the usefulness of a new ultrashort contrast-enhanced (CE) MR angiography (MRA) for the morphologic evaluation of cerebral arteriovenous malformations (AVMs). The method was compared with conventional X-ray digital subtraction angiography (DSA) and time-of-flight (TOF) MRA in 22 patients to assess the angioarchitecture of the malformations which is essential for treatment planning and follow-up. Two experienced MR readers independently evaluated both techniques with regard to the assessment of feeding arteries, AVM nidus, and venous drainage patterns. Contrast-enhanced MRA was able to detect all AVMs seen on DSA, whereas the TOF MRA failed in 1 patient with a very small AVM. In the assessment of the different vessel components of the AVM there was no difference for the detection and delineation of feeding arteries and the AVM. The venous drainage patterns could always be clearly delineated in the CE MRA, whereas TOF MRA could demonstrate the exact venous drainage in only 9 patients. Contrast-enhanced MRA was found to be superior to conventional TOF MRA in the assessment of the angioarchitecture of cerebral AVMs especially regarding the assessment of the venous drainage patterns. The superiority is supported by the improved vessel-to-background contrast and contrast-to-noise ratios. The major limitations of this new technique consist of a low spatial resolution at the used time resolution which can be improved by further sequence modifications. Contrast-enhanced MRA is thus an important additional imaging technique for treatment planning and follow-up of AVMs.

Postoperative fluid-attenuated inversion recovery MR imaging of cerebral gliomas: initial results

Fluid-attenuated inversion-recovery (FLAIR) imaging has shown to be a valuable imaging modality in the assessment of intra-axial brain tumors; however, no data are available about the role of this technique in the clinically important postoperative stage. The purpose of this study was to evaluate the diagnostic potential of FLAIR MR imaging in residual tumor after surgical resection of cerebral gliomas. Fifteen patients with residual cerebral gliomas were examined within the first 18 days after partial surgical resection of cerebral gliomas. The imaging protocol included T1-weighted spin echo, T2- and proton-density-weighted fast spin echo, and FLAIR imaging with identical slice parameters. T1 and FLAIR were repeated after contrast media application. Detection and delineation of residual tumor were the primary parameters of the image analysis. Additionally, the influence of image artifacts on the image interpretation was assessed. On FLAIR images residual signal abnormalities at the border of the resection cavities were observed in all patients, whereas T2- and T1-weighted images present residual abnormalities in 13 of 15 and 10 of 15 patients, respectively. The FLAIR imaging was found to be superior to conventional imaging sequences in the delineation of these changes and comparable to contrast enhanced T1-weighted imaging in the delineation of residual enhancing lesions. Because of protein cell components and blood byproducts within the resection cavity, FLAIR imaging was unable to suppress the cerebrospinal fluid (CSF) in 4 patients. After the decomposition of proteins and blood, CSF could again be completely suppressed and residual or recurrent tumors were clearly identified. Our preliminary study has shown that FLAIR may be a valuable diagnostic modality in the early postoperative MR imaging after resection of cerebral gliomas due to its better delineation of residual pathologic signal at the border of the resection cavity. It should therefore be integrated into the early and/or intraoperative MR imaging protocol.

Differentiation of radiation necrosis from tumor progression using proton magnetic resonance spectroscopy

We report on a young woman who was treated by stereotactic radiotherapy for recurrence of an initially resected low-grade astrocytoma. MRI follow-up examination 7 months after radiotherapy showed a gadolinium-DTPA-enhancing mass lesion indicative of high-grade tumor progression. This assumption was also supported by positron emission tomography with [2-18F]fluoro-2-deoxy-D-glucose (FDG-PET). In contrast, proton MR spectroscopy (1H-MRS) indicated radiation necrosis, which was confirmed histopathologically in surgical specimens. Subsequent follow-up examinations up to 19 months after surgery showed no evidence of tumor recurrence.

Changes of tumor vascularity during gene therapy monitored with color Doppler US

Using contrast-enhanced color Doppler (CD) sonography, we assessed alterations of tumor blood flow induced in 25 murine Morris hepatomas transfected with a gancyclovir- (GCV-)sensitizing Herpes simplex virus thymidine kinase (HSVtk) suicide gene in combination with systemic GCV treatment and compared findings with a control tumor. CD measurements were quantified by the color pixel density (CPD) and the mean encoded flow velocity (mean color value, MCV), using computer-assisted image analysis, and compared with histologic arteriole counts. During 5 days, the tumor volume remained constant. In HSVtk-expressing tumors, the median CPD dropped from 16% at baseline to 5% on day 5 (p = 0.001), remaining constant in controls. The MCV decreased from 1.9 cm/s to 1.6 cm/s in the HSVtk-expressing tumors (p = 0.001) and rose from 1.8 cm/s to 2.0 cm/s in the controls (p = 0.002). In an accompanying histologic arteriole assay, we found no alterations attributable to treatment.

Bone marrow microcirculation analysis in multiple myeloma by contrast-enhanced dynamic magnetic resonance imaging

The aim of our study was to investigate the quantitative microcirculation parameters amplitude A (hypothetical intravascular volume) and exchange rate constant k(21) (hypothetical vascular permeability) by contrast-enhanced dynamic magnetic resonance imaging (dMRI) as markers of angiogenesis in multiple myeloma (MM). Therefore lumbar spine and spina iliaca superior posterior of 16 normal controls and 41 patients with active MM were assessed using a dMRI protocol with a pump controlled bolus infusion of Gadolinium-DTPA. Pharmacokinetic parameters, amplitude A and exchange rate constant k(21) were calculated according to a 2-compartment model. Color-coded parameter images were generated from pharmacokinetic data analysis and superimposed onto the conventional MR images. Amplitude A and k(21) parameters were significantly increased in patients with MM compared with controls (p = 0.001; median A(ctr), 0.2 [range, 0.09-0.4]; median A(MM), 0.93 [range, 0.2-2.2]; median k(21ctr), 0.09 min(-1) [range, 0.03-0.9]; median k(21MM), 4.58 [range, 0.22-23.8]). Within the group of MM patients the pattern of color-coded parameter images were found to be either of "diffuse" (n = 13, 31%) or "focal" (n = 28, 69%) type of distribution of microcirculation. Comparison of amplitude A in patients with "focal" vs. "diffuse" pattern of the pharmacokinetic maps revealed a significant increase in the median of amplitude A in the "focal" group. Amplitude A values allowed a classification of patients according to severe osteolytic bone involvement (p = 0.023) with the best cutoff value of 0.7 for amplitude A. Downmodulation of amplitude A was observed in a MM patient treated with standard VAD chemotherapy. Our data demonstrate that dMRI is a novel imaging technique for the detection and monitoring of MM bone lesions. It provides independent evidence for angiogenesis in MM.

Proton MR spectroscopic evaluation of suspicious brain lesions after stereotactic radiotherapy

BACKGROUND AND PURPOSE

The radiologic assessment of suspicious brain lesions after stereotactic radiotherapy of brain tumors is difficult. The purpose of our study was to define parameters from single-voxel proton MR spectroscopy that provide a probability measure for differentiating neoplastic from radiation-induced, nonneoplastic lesions.

METHODS

Seventy-two lesions in 56 patients were examined using a combined MR imaging and MR spectroscopy protocol (point-resolved spectroscopy, TE = 135 ms). Signal intensities of cholines, creatines, N-acetyl aspartate, and the presence of lactate and lipid resonances were correlated to final diagnoses established by clinical and MR imaging follow-up, positron emission tomography studies, or biopsy/surgery. Statistical analysis was performed using the t test, linear discriminant analysis, and k nearest-neighbor method.

RESULTS

Significantly increased signal intensity ratios I(tCho)/I(tCr) (P <.0001) and I(tCho)/I(NAA) (P <.0001) were observed in neoplastic (n = 34) compared with nonneoplastic lesions (n = 32) and contralateral normal brain (n = 33). Analysis of I(tCho)/I(tCr) and I(tCho)/I(NAA) data yielded correct retrospective classification as neoplastic and nonneoplastic in 82% and 81% of the lesions, respectively. Neither I(NAA)/I(tCr) nor signal intensitities of lactate or lipids were useful for differential diagnosis.

CONCLUSION

Metabolic information provided by proton MR spectroscopy is useful for the differentiation of neoplastic and nonneoplastic brain lesions after stereotactic radiotherapy of brain tumors.

Fluid-attenuated inversion-recovery MR imaging of gliomatosis cerebri

Magnetic resonance imaging has been shown to be the most sensitive imaging modality in the assessment of gliomatosis cerebri. Recent studies have shown that fluid-attenuated inversion-recovery (FLAIR) is a valuable MR sequence in the delineation of cerebral pathologies including intra-axial tumors. However, no data are available about the role of this novel technique in the assessment of gliomatosis lesions. The purpose of this study was therefore to evaluate the diagnostic potential of FLAIR MR imaging in patients with suspected gliomatosis cerebri. Seven patients suspected of having lesions of gliomatosis cerebri were examined by T1-weighted spin echo (SE), T2-weighted fast spin echo (FSE), and FLAIR MR imaging with identical slice parameters. T1 and FLAIR were repeated after contrast media administration. Delineation and extent of gliomatosis were the primary parameters of the image analysis. The FLAIR imaging clearly delineated the extent of gliomatosis lesions in all patients. Due to the suppression of cerebrospinal fluid, the delineation was superior to conventional T2-weighted FSE images. Especially the detection and delineation of cortical spread and the infiltration of the corpus callosum was best seen on FLAIR images. The FLAIR MR imaging is a valuable diagnostic modality in the assessment of patients with gliomatosis cerebri. Due to its better delineation of tumor spread, it was found to be the imaging method of choice and should therefore be integrated into the MR imaging protocol of these patients.

Transient enlargement of contrast uptake on MRI after linear accelerator (linac) stereotactic radiosurgery for brain metastases

PURPOSE/OBJECTIVE

With the increasing number of patients successfully treated with stereotactic radiosurgery for brain metastases, decision making after therapy based on follow-up imaging findings becomes more and more important. Magnetic resonance imaging (MRI) is the most sensitive means for follow-up studies. The objective of this study was to investigate the treatment outcome of our radiosurgery program and to describe the response of brain metastases to contrast-enhanced MRI after linear accelerator (linac) stereotactic radiosurgery and identify factors to distinguish among local control and local failure.

METHODS AND MATERIALS

Using serial MRI, we followed the course of 87 brain metastases in 48 consecutive patients treated between September 1996 and November 1997 with linac-based radiosurgery with 15-MV photons. Treatment planning was performed on an MR data cube. For spherical metastases, radiosurgery was delivered using a 9 noncoplanar arc technique with circular-shaped collimators. For irregularly shaped targets, radiosurgery was delivered using a manually driven multi-leaf collimator with a leaf width of 1.5 mm projected to the isocenter. Median radiosurgery dose was 20 Gy prescribed to the 80% isodose. Together with whole brain radiotherapy (20 x 2 Gy, 5/w), a median radiosurgical dose of 15 Gy was delivered. Median follow-up was 8 (range 2--36) months. Factors influencing local control and survival rates were analyzed with respect to MRI response, and Kaplan-Meier curves were calculated.

RESULTS

Actuarial local tumor control was 91% at one and two years. Patient survival at one and two years was 30% and 18%. Median survival was 9 months. During follow-up in 70 (81%) of the 87 treated metastases, the contrast-enhancing volumes on T1W images were stable or disappeared partly or completely. A transient enlargement of contrast-enhancing volumes was observed in 11 (12%) of the 87 lesions treated, while a progressive enlargement due to local treatment failure was observed in 6 (7%) of the 87 treated metastases. Younger age, early contrast onset after radiosurgery, and previous chemotherapy were associated with this transient enlargement of contrast-enhancing lesion volume.

CONCLUSIONS

Linac-based radiosurgery is an effective, noninvasive, and safe treatment option for patients with brain metastases. A marked enlargement of the contrast-enhancing volume on T(1)-weighted MR images after radiosurgery is a sensitive predictor for, but not equivalent with, local failure. In as many as two-thirds of the cases with contrast enlargement in MRI follow-up, the contrast enlargement is transient with no need for further treatment. While some MRI findings are more likely if transient enlargement is present, a clear decision cannot be made based on MRI, and ultimately the clinical status dictates further action.

[Imaging the smallest tumor vessels using color Doppler ultrasound in an experiment]

PURPOSE

We present an experimental, statistical approach to estimate the size required for small vessels to become detectable with color Doppler sonography.

MATERIALS AND METHODS

A murine experimental tumor was examined with color Doppler sonography after injection of 1.5 ml of the contrast medium Levovist. Histologically, we measured vessel diameters inside the tumor as well as other, clearly identifiable locations.

RESULTS

With color Doppler at a transmit frequency of 7 MHz, vessels were only detected in the tumor's environment, but not inside. From the 95% quantiles of the vessel diameter distribution found histologically, we estimate that vessels 80-140 microns in diameter or above may be detectable with color Doppler sonography, while vessels 40 microns in diameter or smaller are indetectable.

CONCLUSIONS

Although a direct sonographic--histologic correlation is impossible for small vessels, a systematic assessment of the size distribution in clearly identifiable regions permits to estimate the sensitivity of color Doppler to detect blood flow in small vessels. According to our results, capillary blood flow is indetectable, and precapillary vessels may be detected only under optimal conditions.

[HIRE (high intensity reduction). New cerebrospinal fluid suppressed T2-weighted imaging sequence]

PURPOSE

The HIRE sequence utilizes the very long T2 value of CSF to suppress its high signal contribution in T2-weighted imaging by an image subtraction technique.

METHODS

To assess the diagnostic potential of a new dark fluid sequence HIRE (High Intensity REduction) in the diagnostic work-up, 20 patients with histologically confirmed cerebral gliomas were examined with T2-weighted FSE, T1-weighted SE, fast FLAIR and HIRE using identical scan parameters. In patients with enhancing lesions fast FLAIR and HIRE were added to the contrast-enhanced T1-weighted SE images. Images were analyzed in a qualitative and quantitative evaluation. In the qualitative lesion analysis, lesion delineation and differentiation between enhancing and non enhancing tumor tissue were by two readers. For the quantitative analysis lesion-to-background and lesion-to-CSF contrast and contrast to noise ratios were determined in an region of interest analysis.

RESULTS

HIRE achieved a significant reduction of the CSF signal without loosing the high gray-to-white matter contrast of T2 weighted sequences. In the quantitative analysis, the contrast ratios of the HIRE were lower compared to the FLAIR images due to a relative high background and CSF signal. After the application of contrast media HIRE images revealed a significant signal increase in enhancing lesions, which subsequently increased the contrast and contrast-to-noise ratios. In the qualitative analysis, both readers found all tumors clearly delineated on HIRE imaging. Compared to T2-weighted FSE the tumor delineation with HIRE was better in nine patients, equal in four patients and less in one patient. Compared to the FLAIR images HIRE was rated superior in three patients, equal in nine patients and inferior in another three patients. Delineation of the enhancing tumor parts was possible with HIRE in all patients. HIRE images present significant less image artifacts than FLAIR images due to reduced inflow effects.

CONCLUSIONS

The presented T2 based HIRE sequence is an alternative to the T1 based FLAIR sequence with the advantage of a better gray to white matter contrast and shorter measurement time. Due to the subtraction technique signal intensities from tissues with T2 relaxation times in the range between white matter and CSF are also partially affected depending on their T2 values. With respect to this undesired effect, an improvement in HIRE imaging will be expected by a self-weighted subtraction algorithm.

[Quantitative recording of renal function with magnetic resonance tomography]

AIM

To show the potential of various methods in magnetic resonance imaging for the evaluation of renal function.

MATERIAL AND METHODS

A combined assessment of renal morphology, renal hemodynamics and function is proposed. Various techniques are explained, including multiphasic 3D gadolinium MR angiography, MR phase-contrast flow measurements, quantitative perfusion measurements with intravascular contrast agents, and MR renography and MR urography. The use of these techniques is demonstrated for renovascular diseases.

RESULTS

The combined use of these techniques allows renal artery stenosis to be accurately detected and evaluation of renal blood flow, perfusion, glomerular filtration rate, and renal excretion. Based on true quantitative parameters, the hemodynamic and functional significance of the stenosis can be assessed. Renovascular diseases can be differentiated from renoparenchymal disease.

CONCLUSION

For the assessment of renal function, functional magnetic resonance imaging techniques are an important alternative to nuclear medicine. The predictive value regarding the effect of revascularization is currently under investigation.

[Functional magnetic resonance tomography in neuroradiology]

The assessment of cerebral functions has long been the domain of positron-emission tomography and single photon emission computed tomography. The use of rapid imaging sequences and contrast agents enables physiological and pathophysiological cerebral processes to be assessed and monitored by magnetic resonance imaging. Both T1- and T2-weighted contrast-enhanced fast imaging sequences can be used to assess tissue perfusion, vascularity, and microcirculation by applying models developed in nuclear medicine. The diffusion of water molecules and hemodynamic aspects of the macrovasculature can also be monitored. Functional magnetic resonance (MR) imaging enables the visualization of neuronal function and activity, and MR spectroscopy makes possible the metabolic mapping of lesions and surrounding tissue. The advantages of MR techniques includes their low invasiveness, multiplanar imaging ability, and lack of radiation. This contribution discusses the clinical use of functional MR imaging methods and their role in neuroradiological diseases. Measuring perfusion and diffusion allows detailed insight into the pathophysiology of cerebral ischemia and is already being used routinely in acute ischemic stroke. Dynamic MR angiography enables the hemodynamic assessment of vascular malformations. In CNS neoplasms these imaging techniques can improve lesion characterization and the selecting, planning, and monitoring of therapy. Functional MR imaging techniques have also revolutionized the study of psychiatric illness; however, their clinical utility here is still limited. Initial results in patients with dementia and schizophrenia have provided insight into the pathophysiological changes of these diseases.

[Functional magnetic resonance tomography in the diagnosis and therapy monitoring in multiple myeloma]

AIM OF THE STUDY

Investigation of the quantitative microcirculation parameters amplitude A and exchange rate constant k21 determined by contrast-enhanced dynamic magnetic resonance imaging (d-MRI) in multiple myeloma (MM).

METHODS

d-MRT of lumbar spine and right spina iliaca superior posterior of 16 controls (ctr) and 35 patients with active MM. Generation of colour-coded images of microcirculation parameters superimposed onto static MRI images.

RESULTS

Amplitude A and k21 parameters were significantly increased in patients with MM and down modulated by therapy in 7 of 8 MM cases in a follow-up investigation [p < 0.01; median Actr = 0.2 (0.09-0.4); median AMM = 0.93 (0.2-1.52); median k21ctr = 0.09 min-1 (0.03-0.9); median k21MM = 4.57 min-1 (0.21-23.8)]. Thirteen patients revealed a "diffuse" and 22 a "focal" pattern of distribution of microcirculation parameters. Bone marrow biopsies in 8 cases revealed an correlation between bone marrow plasma cell infiltration and increased microcirculation parameters.

CONCLUSION

Identification of microcirculation changes by d-MRI is a novel imaging technique for the detection and monitoring of MM bone lesions.

Disappearance of tumor contrast on contrast-enhanced FLAIR imaging of cerebral gliomas

Contrast-enhanced fluid-attentuated inversion recovery (FLAIR) magnetic resonance (MR) imaging has shown to be a valuable diagnostic modality in the assessment of cerebral gliomas. In this study we report of a potential pitfall regarding the delineation of enhancing tumor parts on contrast enhanced FLAIR imaging. In a limited number of patients, the administration of gadolinium obscures the area of contrast enhancement on contrast enhanced FLAIR images. Therefore the delineation of the macroscopic tumor parts, which are of great importance for the treatment planning is substantially worsened.

Assessment of cerebral gliomas by a new dark fluid sequence, high intensity REduction (HIRE): a preliminary study

The purpose of this study was to assess the diagnostic potential of a new dark fluid sequence, high intensity reduction (HIRE) in the diagnostic workup of patients with cerebral gliomas. The HIRE sequence utilizes a very long T(2) value of the cerebrospinal fluid (CSF) to suppress its high signal contribution in T(2)-weighted imaging by a image subtraction technique. Fifteen patients with histologically confirmed cerebral gliomas were examined with T(2)-weighted fast spin-echo (FSE), T(1)-weighted SE, fast fluid-attenuated inversion recovery (FLAIR), and HIRE imaging using identical scan parameters. In patients with enhancing lesions, fast FLAIR and HIRE were added to the contrast-enhanced T(1)-weighted SE images. Images were analyzed in a qualitative and quantitative evaluation. In the qualitative analysis, lesion detection, lesion delineation, and differentiation between enhancing and non-enhancing tumor tissue were assessed in a two-reader study. For the quantitative analysis, lesion-to-background and lesion-to-CSF contrast and contrast-to-noise ratios were determined in a region of interest analysis. HIRE achieved a significant reduction of the CSF signal without losing the high gray-to-white matter contrast of T(2)-weighted sequences. In the quantitative analysis, the contrast ratios of the HIRE images were lower compared with the FLAIR images due to a relatively high background and CSF signal. After administration of contrast media, HIRE images presented a significant signal increase in enhancing lesions, which subsequently increased the contrast and contrast-to-noise ratios. In the qualitative analysis, both readers found all tumors clearly delineated on HIRE imaging. Compared with T(2)-weighted FSE, the tumor delineation with HIRE was better in nine patients, equal in four patients, and less in one patient. Compared with the FLAIR images, HIRE was rated superior in three patients, equal in nine patients, and inferior in another three patients. Delineation of the enhancing tumor parts was possible with HIRE in all patients. HIRE images had significantly fewer image artifacts than FLAIR images due to reduced inflow effects. The T(2)-based HIRE sequence presented is an alternative to the T(1)-based FLAIR sequence, with the advantage of better gray-to-white matter contrast and shorter measurement time. Due to the subtraction technique, signal intensities from tissues with relaxation times in the range T(2 WM) < < T(2) < T(2 CSF) are also gradually affected, corresponding to their T(2) values. With respect to this unwanted effect, an improvement in HIRE imaging will be possible by using a self-weighted subtraction algorithm. In a forthcoming study this concept will first be tested on appropriate phantom fluids.

Afferent-efferent vessel dysfunction appears to be a specific characteristic of a large subset of patients with essential hypertension

Exercise renography makes it possible to subdivide essential hypertensives (EHs) into two distinct populations. Fifty to 60% develop exercise-mediated renal dysfunction and a transitory, severe reduction of glomerular filtration. The other subset of EHs does not have exercise-mediated renal dysfunction. We hoped to learn whether the disturbance is also present while EHs rest. Twenty-six EHs and 21 normotensive controls were studied with a resting sequential renogram using Tc-99m-mercaptoacetyl-triglycine (MAG3), a tracer excreted primarily by proximal tubular cells. EHs also had an exercise renogram. All persons had three consecutive 10-min dual-tracer infusion clearance determinations with 111In-DTPA and 131I-hippurate, for the simultaneous determination of glomerular filtration rate (GFR) and effective renal plasma flow (ERPF). To demonstrate the accuracy of the clearance procedure we sought to reproduce Hollenberg's results which show greater flow variability in EH than in normotension. Following this, the variability (VAR) of the GFR and ERPF as well as the variability fraction (VF), the ratio of GFR variability divided into the ERPF variability, were calculated. Hollenberg's results were reproduced. Sixteen of 26 essential hypertensives developed exercise-mediated renal dysfunction. GFR-VAR in EH differed from controls. The VF suggests that EHs with a bilateral abnormal exercise renogram have a more pronounced GFR variability than those EH with a normal exercise renogram. The results point to intraglomerular pressure fluctuations in patients with EH, and the VF suggests that this may be more pronounced in EHs with a bilateral abnormal exercise renogram than in those with a normal exercise renogram. It is hypothesized that the variable GFR provokes renin secretion in EH.

[Optimizing temporal resolution in CT with retrospective ECG gating]

PURPOSE

Spiral CT of the heart using the established ways of ECG synchronization is hampered by the relatively long acquisition times of 250 to 500 ms. This only allows to acquire diastolic images in patients with moderate heart rates. In this work, algorithms for time-optimized retrospective cardiac gating are presented, and their potential to improve temporal resolution is investigated.

MATERIAL AND METHODS

These algorithms use data from multiple gantry rotations for image reconstruction, which is possible for multi-scans at fixed slice positions as well as for overlapping spiral scans. Temporal resolution was quantified using computer simulations and compared to experimental data from pigs.

RESULTS

Using a conventional sub-second CT scanner, considerably higher temporal resolutions are possible with spiral scanning. A temporal resolution of 170 ms already provides systolic images with little motion artifacts. Higher temporal resolutions of up to 70 ms are demonstrated for multi-scans, which allows to depict ventricle wall movement over the complete cardiac cycle.

DISCUSSION

The method of time-optimized retrospective cardiac gating broadens the spectrum of conventional spiral-CT for cardiac imaging. It can be directly transferred to multi-slice scanners. Here it can be used clinically because of reduced scan time. Potential applications are the determination of functional cardiac parameters like ejection fraction and the detection of disorders of ventricle wall movement.

[Improved tumor contrast and delineation in the stereotactic radiotherapy planning of cerebral gliomas and metastases with contrast media-supported FLAIR imaging]

BACKGROUND

FLAIR MR imaging has shown to be a valuable imaging modality in pathologic lesions of the brain including intra-axial brain tumors. The aim of the study was to assess the value of a FLAIR technique in the planning process of stereotactic radiotherapy in patients with cerebral gliomas and metastases.

PATIENTS AND METHODS

Thirty-five patients with cerebral gliomas and 12 patients with a total of 39 cerebral metastases were examined by T2/PD-weighted fast spin-echo, fast FLAIR prior and after contrast and contrast enhanced T1-weighted spin-echo using identical slice parameters. The images were evaluated by using quantitative and qualitative criteria. Quantitative criteria were tumor-to-background and tumor-to-cerebrospinal fluid contrast and contrast-to-noise. The qualitative evaluation was performed as a multireader analysis concerning lesion detection, lesion delineation and image artifacts.

RESULTS

In the qualitative evaluation (Table 3 and 6), all readers found the fast FLAIR images to be superior to fast spin-echo in the exact delineation of cerebral tumors (p < 0.001) and the delineation of enhancing and non enhancing tumor parts. Fast FLAIR was superior in the delineation of cortically located and small lesions but was limited in lesions adjacent to the ventricles. Fast FLAIR provided a significantly better tumor-to-CSF contrast and tumor-to-CSF contrast-to-noise (p < 0.001) (Tables 1, 2a, 2b, 4, 5). The tumor-to-background contrast and tumor-to-background contrast-to-noise of the fast FLAIR images were lower than that of T2-weighted spin-echo images but were significantly increased after the application of contrast media. FLAIR images had more image artifacts, but the image interpretation was not influenced.

CONCLUSIONS

FLAIR MR imaging was found to be a valuable sequence in the planning protocol of stereotactic radiotherapy. The concurrent presentation of enhancing and non enhancing tumor tissue on contrast enhanced fast FLAIR imaging enables to use a single imaging sequence in the treatment protocol. This enables to load a reduced image amount into the radiotherapy planning software, is therefore time saving and reduces potential errors.

The german thorotrast study: recent results and assessment of risks

The German Thorotrast study comprises 2,326 patients and 1,890 controls. Forty-eight Thorotrast patients and 239 controls are still alive and are invited for a follow-up examination every 2 years. In the deceased patients, the following neoplastic diseases with excess rates were registered (Thorotrast/controls): liver cancer (454/3); cancer of the bile ducts, including gallbladder (42/7); myeloid leukemia (40/7); myelodysplastic syndrome (30/4); plasmacytoma (10/2); non-Hodgkin's lymphoma (15/5); bone sarcoma (4/1); malignant peritoneal or pleural mesothelioma (9/0). Dose calculations are based on results of whole-body counting, X-ray films, and data obtained from the hospital records on the volume of Thorotrast injected. For liver cancer, the cumulative risk estimate was calculated to be 40 per 10(4) person Sv (radiation weighting factor = 20). These figures are close to the results of the Danish study and are comparable to the results of the Life Span Study of A-bomb survivors after 40 years at risk with 18 to 48 liver cancers per 10(4) person Sv. For hematopoietic malignancies, the cumulative risk was calculated to be about 7 per 10(4) person Sv (radiation weighting factor = 20). This risk estimate is lower by a factor of 10 compared to the results of the Life Span Study.

Non-invasive assessment of renal artery stenosis: current concepts and future directions in magnetic resonance angiography

Magnetic resonance angiography is undergoing rapid development as a non-invasive technique to reliably assess renal artery stenosis. Invasive X-ray angiography is currently the gold standard imaging technique and gives excellent spatial resolution. However, its disadvantages include a necessary exposure to radiation and the need for iodinated contrast media. While magnetic resonance angiography does not have these disadvantages, its spatial resolution is inherently lower. On the other hand, magnetic resonance angiography enables true three-dimensional imaging. The use of rapid imaging techniques allows multiple image acquisition within one breath-hold thereby permitting the visualization of distinct vascular phases. The limitation in spatial resolution can be overcome readily by combining morphologic imaging with functional information on the hemodynamic relevance. This can be achieved by means of magnetic resonance phase contrast flow measurements. The use of such a combined approach enables the grading of vascular stenosis based on the combination of morphology and functional information. Magnetic resonance angiography is already able to demonstrate a clinical utility equivalent to that of invasive procedures, indicating that it is likely to become a premier method for the diagnosis and follow up of renovascular disease.

Pathophysiologic basis of contrast enhancement in breast tumors

While the diagnostic benefits of gadolinium (Gd)-chelate contrast agents are firmly established in magnetic resonance imaging (MRI) of tumors, the pathophysiologic basis of the enhancement observed and its histopathologic correlate remained vague. Tumor angiogenesis is fundamental for growth and metastasis and also of interest in new therapeutic concepts. By correlative analysis of a) histology; b) vascular density (CD31); and c) vascular permeability (vascular permeability factor/vascular endothelial growth factor [VPF/VEGF]), we found a) significantly (P < 0.001) faster exchange rates in malignant compared with benign breast lesions; b) distinct differences in enhancement characteristics between the histologic types (invasive ductal carcinoma, invasive lobular carcinoma, and ductal carcinoma in situ); and c) dependence of enhancement kinetics on the VPF/VEGF expression. The pathophysiologic basis for the differences in contrast enhancement patterns of tumors detectable by MRI is mainly due to vascular permeability, which leads to more characteristic differences than vascular density. MRI is able to subclassify malignant breast tumors due to their different angiogenetic properties.

Cervical carcinoma: standard and pharmacokinetic analysis of time-intensity curves for assessment of tumor angiogenesis and patient survival

Since detailed knowledge regarding the pathophysiological properties which in turn are responsible for differences in contrast enhancement--remain fairly undetermined, it was the aim of this study (i) to examine the association of standard and pharmacokinetic analysis of time-intensity curves in dynamic MRI with histomorphological markers of tumor angiogenesis (microvessel density [MVD]; vascular endothelial growth factor [VEGF]); and (ii) to determine the ultimate value of a histomorphological and a dynamic MRI approach by correlation of those data with disease outcome in patients with primary cancer of the uterine cervix. Pharmacokinetic parameters (amplitude A, exchange rate constant k21) and standard parameters (maximum signal intensity (SI)-increase [SI-I] over baseline and steepest SI-upslope per second [SI-U/s]) were calculated from contrast-enhanced dynamic MR imaging series in 37 patients with biopsy-proven primary cervical cancer. On the surgical whole mount specimens, histomorphological markers of tumor angiogenesis (MVD, VEGF) were compared with similar sized and positioned regions-of-interest (ROIs) on the MRI-derived parameters. For MRI and histomorphological data, Kaplan-Meier survival curves were calculated and compared using log-rank statistics. A significant association was found between MVD and amplitude A (P < 0.01) and SI-I (P < 0.05). No significant relationships were observed between the VEGF expression and all dynamic MRI parameters. Kaplan-Meier curves based on k21 and SI-U/s showed that tumors with high k21 and SI-U/s values had a significantly (P < 0.05, 0.001, respectively) worse disease outcome than tumors with low k2, and SI-U/s values. None of the histomorphological gold standard markers for assessing tumor angiogenesis (MVD, VEGF) had any significant power to predict patient survival. It is concluded that (1) the pathophysiological basis for differences in dynamic MRI is MVD but not VEGF-expression; (2) a functional, dynamic MRI approach (both standard and a pharmacokinetic analysis) may be better suited to assess angiogenic activity in terms of patient survival than current histomorphological-based markers of tumor angiogenesis; and [3] compared with standard analysis, a simple pharmacokinetic analysis of time-intensity curves is not superior to assess MVD or patient survival.

[Multiphase, contrast-enhanced 3D-MR angiography for morphological and functional focal lesion detection. Initial results]

PURPOSE

To investigate the value of multiphase breath-hold 3D gadolinium (Gd)-enhanced MR angiography (MRA) for lesion detection and characterization of focal liver lesions.

MATERIALS AND METHODS

Breath-hold 3D Gd-enhanced MRA was performed in 25 patients with benign and malignant hepatic lesions on a 1.5-T MR system using an ultrafast 3D spoiled gradient echo sequence (TR/TE =5/2 ms, FOV=300-450 mm, matrix=256x168, voxel volume=1.8x2.3 x2.5 mm, 64 partitions, central k-space reordering; acquisition time=27 s). Three measurements were done in the arterial, portal venous, and late venous phase.

RESULTS

The analysis of the spatial and temporal evolution of contrast enhancement of the 3D-MRA improved significantly (P<0.01) lesion detection and characterization if compared with T1 precontrast, T2-weighted, and T1 postcontrast images.

CONCLUSION

Multiphase breath-hold 3D Gd-enhanced MRA imaging is a robust new technique to significantly improve morphological detection of benign and malignant lesions during the early arterial phase and further improves functional characterization of liver lesions by a combination of an arterial, a portal venous, and a late venous phase. Schlüssselwörter Multiphasisch. MR-Angiographie. Leberläsionen

[Thorotrast-induced liver cancer: results of the German thorotrast study]

AIMS

The X-ray contrast medium Thorotrast, used worldwide between 1930 to 1950 predominantly for arteriography, consisted of a colloidal solution of thorium dioxide. The radioactive thorium-232 (half-life 1.4x10(10) years) is stored lifelong in the organs of the reticulo-endothelial system after intravascular injection, causing chronic exposure to alpha radiation. The aim of the German Thorotrast study is the assessment of radiation late effects and the calculation of risk estimates.

MATERIAL AND METHODS

The German Thorotrast study started in 1968 as a cohort study and comprises 2326 Thorotrast patients and 1890 patients of a matched control group. The Thorotrast patients who were still alive at the beginning of the study were examined by X-ray plain films of the upper abdomen and of the injection site of the contrast medium as well as by whole-body counter measurements. At the beginning we offered the patients ultrasound and later on CT and MRI at regular intervals for early detection of liver cancer.

RESULTS

To date 454 primary liver cancers have been registered in the group of Thorotrast patients compared to 3 cases in the control group. With the help of modern imaging methods relatively small liver cancers were detected and could be surgically removed.

DISCUSSION

There is a correlation between the mean accumulated dose to the liver and the incidence of liver cancer. The cumulative risk for liver malignancies is about 600 diseases per 10(4) persons whose liver was exposed to 1 Gy. Also the incidence of liver cirrhosis is correlated with the mean accumulated dose to the liver.

Renal arteries: optimization of three-dimensional gadolinium-enhanced MR angiography with bolus-timing-independent fast multiphase acquisition in a single breath hold

PURPOSE

To compare two different three-dimensional (3D) gadolinium-enhanced magnetic resonance (MR) angiographic techniques.

MATERIALS AND METHODS

In 26 patients suspected of having renal artery stenosis, results with fast multiphase 3D MR angiography were compared to those with standard 3D MR angiography in 37 patients. With both techniques, 31-second breath-hold acquisitions were performed. Multiphase angiography comprised five discrete 6.4-second acquisitions without bolus timing, and standard angiography comprised a single acquisition based on test-bolus timing. Two readers evaluated images obtained with both techniques in terms of image quality, artifacts, and vessel conspicuity. Accuracy of findings on the multiphase 3D MR angiograms for assessment of renal artery stenosis was determined by comparing them to digital subtraction angiograms and surgical findings.

RESULTS

In the early arterial phase, multiphase 3D MR angiograms showed no image degradation by venous overlay, whereas standard 3D MR angiograms depicted at least minor overlay in 53 of 83 renal arteries (P < .001). Less parenchymal enhancement in the early arterial phase resulted in a higher vessel conspicuity for the divisions and segmental arteries (P < .001). Both readers detected and correctly graded 18 of 20 stenoses on the multiphase angiograms with almost perfect interobserver agreement (kappa > 0.89).

CONCLUSION

Renal multiphase 3D MR angiography is an accurate technique requiring no bolus timing. The performance of early arterial phase imaging leads to improved depiction, particularly of the distal renovascular tree, compared to that with standard single-phase 3D MR angiography.

[Phosphorus-31-MR spectroscopy imaging in preoperative embolization treatment of meningioma]

PURPOSE

31P MR spectroscopic imaging (31P SI) was evaluated in a clinical study as a method for monitoring presurgical devascularization of meningiomas. The aim was to assess noninvasively metabolic alterations in tumor and in healthy brain tissue before and after embolization.

METHODS

Localized 31P MR spectra of the brain were obtained by means of 2D-SI (voxel size: 36 cm3) using a 1,5-T whole-body MR tomograph.

RESULTS

Eleven of 19 patients with intracranial meningiomas examined in this study underwent preoperative embolization therapy; eight patients were examined before and after treatment. After embolization, alterations of pH and of the concentrations of high-energy phosphates (nucleoside-5' triphosphate = NTP, phosphocreatine = PCr), inorganic phosphate (Pi), and membrane constituents were observed in the tumors. A tendency of [Pi] increase and decrease of [NTP], [PCr], and pH predominated, which is explained by ischemic processes after tumor devascularization.

CONCLUSION

31P SI is applicable in clinical studies and detects alterations of phosphate metabolism in a meningioma after embolization.

Pharmacokinetic imaging of 11C ethanol with PET in eight patients with hepatocellular carcinomas who were scheduled for treatment with percutaneous ethanol injection

PURPOSE

To evaluate the carbon 11 ethanol kinetics with positron emission tomography after intratumoral injection of the tracer and assess its redistribution and dilution in patients who have hepatocellular carcinomas and who were scheduled for treatment with percutaneous ethanol injection.

MATERIALS AND METHODS

The study included eight patients with hepatocellular carcinomas. 11C ethanol was administered via a puncture needle positioned with ultrasonographic guidance. Parametric images based on the Fourier transformation were created for further analysis of the local distribution patterns of the tracer. The ratio of the 45-minute postinjection standardized uptake value to the 5-minute postinjection standardized uptake value was used for the evaluation of ethanol dilution.

RESULTS

Five of eight tumors demonstrated almost constant uptake values after the initial distribution phase. In contrast, a rapid elimination of the 11C ethanol from the tumor was documented in three of eight tumors. The 45 minute-to-5 minute ratio was 0.18-0.67 (median value, 0.56) in the tumors. The time-activity curves of the normal liver parenchyma increased slowly but steadily with time owing to a low ethanol elimination from the tumor. Fourier transformation demonstrated inhomogeneous parts on the amplitude images in seven of eight tumors and random redistribution on the phase images in six of eight tumors.

CONCLUSION

Inhomogeneous drug distribution and drug dilution in the target area are likely to be the major limiting parameters for therapy response.

Alterations of intratumoral pharmacokinetics of 5-fluorouracil in head and neck carcinoma during simultaneous radiochemotherapy

The kinetics of local drug uptake and metabolism of the anticancer drug 5-fluorouracil (5-FU) has been monitored by means of 19F nuclear magnetic resonance spectroscopy in 17 patients with neck tumors during concurrent radiochemotherapy. All of the patients underwent an accelerated hyperfractionated, concomitant-boost radiochemotherapy with 5-FU [600 or 1000 mg/m2 of body surface (b.s.)] and carboplatin (70 mg/m2 of b.s.). Serial 19F nuclear magnetic resonance spectra were obtained during and after the administration of 5-FU in a 15-T scanner with the use of a 5-cm diameter surface coil positioned on a cervical lymph node metastasis. Examinations were performed at day 1 of therapy and, in 13 patients, also after 43.5 Gy of irradiation at day 1 of the second chemotherapy cycle. Resonances of 5-FU and the catabolites 5,6-dihydro-5-fluorouracil (DHFU) and alpha-fluoro-beta-alanine (FBAL) were resolved in the tumor spectra. The median of the 5-FU and FBAL levels was significantly higher (more than 2-fold) at the second compared with the first examination, whereas the level of DHFU did not change. This effect could indicate an increased delivery of 5-FU into the interstitial space of the tumor in the course of the combined treatment, which would result in an enhanced exposure of the tumor cells to the drug. A potential mechanism for synergy between radio- and chemotherapy is discussed, but alternative mechanisms are also being considered. The findings indicate that a method is available to rationally address the design of dosing schedules in concurrent therapy regimens.

[Radiologic diagnosis of the kidneys in dialysis patients]

The kidneys of patients with chronic renal failure undergoing maintenance hemodialysis may show different variances or complications. Most common are secondarily acquired renal cysts, which may be found in as many as 92% of patients after 8 years of hemodialysis. Single (in 12.5% of patients) or multiple (8.3%) cysts with bleeding are common; additionally, hematuria or ruptured cysts may be found. Bleeding into cysts is more common in patients with autosomal dominant polycystic kidney disease. Due to the decreasing urinary production development of kidney stones is very uncommon, but calcifications in or around cysts can be found in 71% of patients. Kidney tumors occur 41 times more often in patients with chronic renal failure than in patients without kidney disease. We detected tumors in 4.2% of our patients on long-term dialysis. Diagnostic differentiation of the relatively slow growing and fairly late metastasizing malignant tumors from adenomas is not possible. Nevertheless, we screen our patients every 3-4 years. Computed tomography is superior to ultrasonography for this purpose, because ultrasonography lacks the necessary sensitivity in this group of patients.

[MRI of the kidneys. New diagnostic strategies]

AIM

New diagnostic strategies for evaluation of the kidney by fast MR imaging techniques.

MATERIAL AND METHODS

A comprehensive morphologic and functional evaluation of the kidney is proposed using fast MR imaging of renal morphology, multiphase 3D gadolinium MR angiography, MR urography and MR flow measurements. A single MR examination is designed to grade renovascular disease and assess the hemodynamic and functional significance, detect and characterize renal lesions and evaluate the urinary tract.

RESULTS

The combined analysis of morphologic and functional data allows reliable assessment of renal artery stenosis, benign and malignant renal masses and diseases of the renal collecting system and ureters, as well as congenital abnormalities in good agreement to the results of conventional imaging modalities. The improved tissue contrast and additional functional information compensates for the disadvantage of a lower spatial resolution.

CONCLUSION

Combined morphologic and functional MR examination represents a reliable, non-invasive and cost-effective alternative imaging modality for comprehensive diagnostic evaluation of renal disease.

Changes in myocardial oxygenation and perfusion under pharmacological stress with dipyridamole: assessment using T*2 and T1 measurements

The aim of this pilot-study was to evaluate changes in myocardial oxygenation and perfusion under pharmacological stress with dipyridamole (DIP) by means of MRI. Twenty healthy volunteers were examined using a multi-echo gradient-echo sequence. The differential myocardial signal response due to the blood oxygen level dependent (BOLD) effect was studied under variable conditions of myocardial oxygen supply caused by the vasodilator DIP. Unlike contrast agents (CA) methods, which require at least two injections of CA and DIP, the presented methods require only a single infusion of DIP. To assess changes in myocardial perfusion, a saturation recovery TurboFLASH (SRTFL) sequence with centric reordering for T1 measurements was used with global and slice-selective spin-preparation (five volunteers). The signal response was measured at baseline conditions and when myocardial blood flow was increased during pharmacological stress with DIP. Administration of DIP induced a 17 +/- 9% increase in T2*. Enhanced perfusion resulted in a 15 +/- 5% decrease of T1 after slice-selective spin preparation and a calculated increase in absolute perfusion of about 5.1 ml/(g x min), which reflects coronary reserve. The study shows that DIP-induced alterations in the relationship between myocardial oxygen supply and demand are detectable in healthy volunteers using T2* and T1 measurements. A combination of T2* and T1 examinations could become a useful diagnostic tool for the non-invasive assessment of myocardial oxygenation and perfusion in patients with coronary artery disease (CAD).