DCEMRI in Comparison with Other Imaging Modalities

From the drug development perspective, DCE-MRI is just one of many ways to provide a biomarker a signal that provides evidence of an acute, maybe pharmacodynamic, response to the investigational agent. Bio-markers might be sought in principle in biofluids (e.g. blood, urine), in accessible non-tumour tissue (e.g. skin), from immunohistochemistry of tumour biopsies or from imaging. Imaging has the advantage that pharmacological responses in the tumour itself can be evaluated and perhaps compared...

Four Oncologic Questions

Radiologists are required to provide information on four clinical questions in imaging primary musculoskeletal neoplasms diagnosis, staging, response to pre-surgical (or initial) chemotherapy1, and detection of recurrence. MRI is useful, together with radiography and clinical data, in narrowing the differential diagnosis and establishing the extent of disease. However, it rarely provides a definitive diagnosis for these tumors. MRI is the pre-eminent imaging modality for the remaining three...

The Validity of the Measurement

It is critical to assess the validity of DCEMRI endpoints as biomarkers or surrogates for the desired parameter. Validation has several aspects which should be distinguished. The strongest validation is validation against outcome (sometimes referred to as predictive validity, an aspect of criterion validity). This is achieved if we can show, for example that tumours with high Ktrans are always associated with a worse prognosis, and that interventions which reduce Ktrans in particular patients...

Reticuloendothelial System RES Contrast Agents

Kupffer cells in the normal liver will take up partic-ulate matter from the circulation and this property has been utilised to produce a group of RES-specific contrast agents. These consist of suspensions of superparamagnetic iron oxide particles (SPIO) or ultra-small superparamagnetic iron oxide particles (USPIO) (Fretz et al. 1989 Weissleder et al. 1989 Weissleder et al. 1990). These agents exhibit strong T1 relaxation properties, and due to susceptibility differences to their surroundings...

Malignant Liver Tumours 14621

Hepatocellular carcinoma is the commonest primary hepatic malignancy (80 -90 ) representing over 5 of all cancers . There are 500,000 to one million new cases each year worldwide (Bruix et al. 2001). It is commoner in developing countries but its incidence is rising in the West. It is commonly associated with liver cirrhosis particularly secondary to high alcohol consumption. HCC develops from dysplastic nodules and there are three steps in development regenerative nodule dysplastic nodule (low...

Signal Intensity Change

The choice of pulse sequence to monitor contrast agent kinetics must satisfy the above criteria but also provide acceptable spatial resolution and tissue coverage. As T2-weighted sequences tend to take more time to collect and the effect of contrast agent on signal intensity is negative i.e. signal decreases with increasing contrast agent concentration hence reducing the signal to noise ratio (SNR) of the experiment , Trweighted sequences offer many advantages. Previously groups have used spin...

Dynamic Contrast Enhanced MRI

A critically important extra-dimension is brought to MRI by the use of exogenous contrast agents namely the time domain. In general, the process of selective accumulation of the tracer is non-instantaneous and thus its dynamics can be interrogated by rapidly repeated imaging. Parametric analysis of this dynamic process often allows physiologically specific inference. Specifically, application of this approach permits the non-invasive evaluation of tissue microvasculature in vivo (Tofts 1997...

Quality Assurance

To ensure that the sequence operated accurately, and provided the correct contrast, a quality assurance protocol was devised. This incorporates a routine QA measurement to be performed on a phantom provided to the centre, that is tailored to fit within the specific breast coil at that centre. This contains a material of known T1 relaxation time and allows T1 relaxation time, signal to noise, and coil homogeneity to be measured (Hayes et al. 1998, 1999). An additional more detailed test...

Quantification

Signal enhancement on Trweighted DCE-MRI images can be assessed in two ways by the analysis of signal intensity changes (semi-quantitative) and or by quantifying contrast agent concentration change or R (R 1 T ) using pharmacokinetic modelling techniques. Semi-quantitative kinetic parameters describe tissue enhancement using of a number of descriptors derived from signal intensity-time curves. These parameters include onset time (time from injection or first appearance in a pelvic artery to the...

Weighted Dcemri of the Prostate

After intravenous contrast medium administration, T1-weighted images can demonstrate prostatic zonal anatomy but in general, unenhanced T2-weighted spin-echo images are better in this regard. On MRI, after the administration of intravenous contrast medium, the normal central gland enhances more than the peripheral prostate both enhancing homogeneously. In the presence of benign prostatic hyperplasia (BPH), enhancement of the central gland becomes heterogeneous (Mirowitz et al. 1993 Brown et al....

Rationale for Dcemri of EFT

MRI is the preferred modality for therapy planning in Ewing's family tumors, for many of the same reasons it is preferred for osteosarcoma therapy planning. Over 50 of EFT occur in the extremities, and limb-salvage surgery is preferred over amputation when possible. MRI shows excellent accuracy in depicting the extension of osseous osteosarcoma and Ewing's tumors to the physis and epiphysis (San Julian et al. 1999). As with osteosarcoma, the gold standard for response of EFT to pre-operative...

Parallel Imaging Techniques

The fact that perfusion is often only studied in a few slices of the brain is occasionally a significant limitation of the study. Future increments in gradient strength and reductions in the gradient switching time may allow the time required for a given matrix to be reduced, albeit with reduced signal-to-noise for the former due to increased sampling bandwidth. Even with today's hardware performance EPI-based DSC-MRI occasionally suffers from inappropriate image quality. Therefore, a...

Future Directions

For chemotherapy to be effective, therapeutic agents must reach target cells (tumor or endothelial) in adequate concentrations and with minimal toxicity to normal tissues (Jain 1996a). Once a blood-borne molecule reaches an exchange capillary, transport across the vessel wall is a function of the surface area of exchange, the transvascular concentration gradient and the interstitial fluid pressure. Tumor interstitial pressure can be much higher than that in normal tissues, to the point of...

Dynamic Contrast Enhanced Imaging

Though T1 measurements may be made in a matter of seconds (Freeman et al. 1994 Tong and Prato 1994), temporal or spatial constraints usually preclude their use for tracking the passage of a contrast agent bolus (especially for 3D measurements). As discussed above, a common experimental approach is to measure T1 before contrast agent administration then image the tissue rapidly during uptake using a fast Trweighted sequence (Brookes et al. 1999). The pre-contrast T1 measure provides estimates of...

Simultaneous Mapping of rCBV and Krans from Drcemri

Simultaneous mapping of rCBV and Ktrans from DRCE-MRI is complicated by the synergistic effects of intravascular and extravascular contrast agent on measured signal intensity. Li et al. (2000b) (Li and Jackson 2003) have described a novel method which uses an initial data decomposition step to derive separate concentration time course data for intravascular and extravascular contrast media. This data decomposition is performed using prior knowledge of the shape of the intravascular contrast...

Multi Centre Trials in Other Conditions

BarKHoF et al. (1997) have considered the requirements for multi-centre trials in multiple sclerosis, identifying the need to establish observer variability over multiple centres, as well as improve quantification methods and compare the different techniques in a multi-centre longitudinal fashion in order to include variation caused by both scanner and segmentation techniques, in addition to biological activity. BarKHoF et al. (1993) report a database developed for recording serial brain MRI...

Respiratory Motion

A number of potential strategies are available to compensate for the errors introduced by respiratory motion in dynamic contrast enhanced studies of the liver. One potential approach is to minimise the movement by encouraging shallow breathing at rest and further reduce the impact by the acquisition of relatively thick slices, which will be affected to a lesser extent by small respiratory excursions. In practice this is clearly unsatisfactory and although it may be used to generate data from...

Techniques Combining T2 T2 or T1

As earlier depicted, the absence of an intact BBB implies that the contrast agent does not remain intra-vascular. Even when only considering the first pass, the extravascular compartment will show contrast uptake (Heiland et al. 1999). To incorporate this effect in the measurement of quantitative hemody-namic parameters, such as rCBV, rCBF, and MTT, combined techniques may be useful, involving simultaneous measurements of the changes in the T1, T2, or T2* relaxation rate. To be insensitive to...

Diffuse Liver Diseases

Diffuse liver diseases such as fatty infiltration, iron deposition and cirrhosis produce changes in mor phology and signal characteristics which can be characterised by MRI. Although these do not represent malignant disease processes cirrhosis in particular is of importance since it is a common association with hepatocellular carcinoma. Cirrhosis does not significantly alter the T1 or T2 relaxation times of liver although it will produce the classic morphological changes of caudate and left...

Quantitative Approaches Using Pharmacokinetic Models

The optimal analysis of DCE-MRI data would be designed to identify specific quantitative physiological parameters which describe the tissue microvascu-lature being observed. We have discussed previously that the distribution of contrast material will be governed by regional blood flow, blood volume, vessel shape and size, endothelial permeability, endothelial surface area, and the size of the EES. In theory an optimal analysis should allow independent assessment of each of these descriptive...

Dynamic Contrast Enhanced Dce Mr Imaging

The terms MR perfusion imaging, and dynamic MR imaging, which are frequently used interchange-aEarly clinical data suggests that DCE MRI can provide functional assessment of tumor microcirculation and angiogenesis that may be used to monitor therapy and or predict therapy outcome in cervical cancer (Figs. 11.1, 11.2). DCE tumor imaging requires Fig. 11.1a,b. High vs. low dynamic enhancement pattern and therapy outcome. Anatomical (T2-weighted images) and microcirculation imaging (dynamic...

Validation Studies of Dynamic Contrast Enhanced MRI

There are numerous imaging and modeling strategies available for the application of DCE-MRI. The results of so many studies are difficult to compare due to the wide variety of existing mathematical models, each having their own assumptions and constraints (Tofts 1997). The DCE-MRI approach is widely used to draw inferences into microvascular parameters such as microvascular permeability, blood volume, and tissue perfusion. Confirmed insight into the whereabouts, and amount of the tracer, at the...

Model Free Quantification

Perhaps the simplest method for providing reliable and reproducible information that has a bearing on the kinetics of contrast agent accumulation is an integration of the concentration of the agent observed in the tissue of interest over time the initial area under curve (IAUC), unit mmol (Evelhoch 1999). The value of IAUC obtained in a tumour is dependent on the period over which integration is performed typically this will be from the time point representing contrast agent administration or...

Stbsue c exp[TE c k

It has been shown, both theoretically and experimentally, that the apparent transverse relaxation rate, R2*, in a volume of interest (VOI) depends on the concentration of the contrast agent within the VOI. Consequently, changes in the transverse relaxation rate relative to a pre-contrast period can be determined from the GE signal-time curve using the relationship, where S(t) is the signal intensity in the VOI at time t, and SO is the mean signal intensity in the VOI for the images acquired...

Tumor Microcirculation Studies

In 1996 Mayr and colleagues reported on a prospective study investigating temporal changes in the tumor perfusion pattern before, during, and after radiotherapy using fast MRI techniques as a predictor of outcome of patients with advanced cervical cancer (Mayr et al. 1996b). This study included 17 patients with stages IB2-IVA cervical carcinoma, who were treated with primary radiation therapy and imaged before, during, and after the course of radiation therapy. Four MR studies were obtained...

Which Dcemri Parameter to Measure

The use of DCE-MRI merely implies that images will be acquired at defined intervals during the uptake and elimination of a contrast agent. For an effective compound given at the top of the dose-response curve, the radiologist's qualitative assessment may reveal an effect of the drug, but this non-quantitative approach lacks statistical power especially in early trials where effects on the tumour, and on the images, at lower doses may be small. For practical drug development some quantitative...

T2Weighted Perfusion

SE-based DSC-MRI exhibits some distinct physical and physiological differences as compared with the GE method. Simulation studies as well as in vivo experiments have demonstrated that SE-based measurements are less sensitive to microvasculature than GE-based techniques. In computer simulations, the sensitivity of a GE-based method is relatively independent of the size and distribution of vessels and capillaries within a given voxel, whereas SE-based methods show a maximum sensitivity for...

Breast Cancer and Angiogenesis

In solid tumours, growth beyond a millimetre cannot occur without vascular support (Folkman 1996). Transgenic animal tumour model experiments have shown that progression from an in-situ to invasive cancer is accompanied by the onset of angiogenesis (Rak et al. 1995). There are a number of clinical examples where vascularization has been related to tumour progression (e.g., in the change from breast ductal carcinoma in-situ to invasive cancer (Gilles et al. 1995) Bose et al. 1996)....

Tumour Characterisation

The ability of DCE-MRI to quantify a range of characteristics of the tumour microvasculature has encouraged many investigators to use this technique as a basis for in-vivo staging of tumours. Correlation of DCE-MRI-based features of the tumour microv-asculature with pathology, therapeutic response and prognosis remains the main goal for future work with these techniques. Even early studies were able to demonstrate a clear relationship between rapid and large increases in signal enhancement and...

Characterizing Individual Tumor Biology

Malignant tumors differ from benign lesions in several regards, notably in having a more active recruitment of neovascularity. This acceleration of angiogenesis is essential for the exponential growth and metastasis of the tumor cells (Folkman 1992). Tumor vessels differ from normal tissue vessels by their structural irregularity (abnormal endothelial cell contours and peculiar branching patterns), heterogeneity (flow, diameter, and spacing), and leakiness to macromo-lecular solutes (Jain 1988...

Pulse Sequence Timing

The optimal timing for breast MRI sequences is dependent on the goal of imaging. This is because high-resolution and short imaging-time requirements represent competing examination strategies on current equipment. A single high sensitivity, high-resolution, fat suppression 3D technique (with voxel sizes less than 1 mm) is sometimes used. This can be performed within approximately 2-4 min which is in the time window where the differential enhancement between malignant and benign lesions is...

References

Alexander AA (1995) To color Doppler image the prostate or not that is the question. Radiology 195 11-13 Barbier EL, Lamalle L, Decorps M (2001) Methodology of brain perfusion imaging. J Magn Reson Imaging 13 496-520 Barke A, l'yasov KA, Kiselev VG et al (2003) Dynamic gadolinium-enhanced MR imaging for radiation therapy monitoring in prostate cancer patients. Proceedings of the International Society of Magnetic Resonance in Medicine, 11th scientific meeting, Toronto, p 1463 Beerlage HP,...

TrWeighted Breast Cancer DCEMRI

A large body of literature has shown that breast cancer enhance earlier and to a greater extent than benign breast diseases on Trweighted DCE-MRI. This difference is most marked in the early period (1-3 min) after bolus contrast medium administration (Kaiser and Zeitler 1989 Flickinger et al. 1993 Gilles et al. 1993 Boetes et al. 1994). However, other investigators have demonstrated that there is an overlap in the enhancement rates of benign and malignant lesions (Heywang et al. 1989 Fobben et...

Conclusions

DCE-MRI has a well established role in the evaluation of patients with diseases when cancer is strongly suspected or has been diagnosed. MRI is used as a supplementary tool to complement conventional methods of breast evaluation because it has excellent problem solving capabilities. Many indications are recognised as discussed in this chapter. Breast MRI is also the method of choice for the evaluation of the augmented breast both for the implant itself and also for the breast tissue around...

Radiotherapy Planning

The choice of appropriate treatment for patients with prostate cancer remains controversial. The most commonly offered treatments include observation only, radical prostatectomy, radiotherapy, hormone ablation treatment, or a combination. Treatment selection is guided by patient age and general condition, tumour stage and histological grade, serum PSA, and patient and physician preferences. External beam radiotherapy treatment failure is often attributed to the need to limit radiation dose...

Introduction

Approximately one third of the American and European population will develop cancer at some time in their lives. The incidence of cancer increases with age, and among middle-aged people cancer is the single greatest cause of mortality. Currently the major treatment options are surgery, radiotherapy, cytotoxic chemotherapy and hormonal modulation. Despite the tremendous improvements in cancer treatment over the past few decades, survival rates for many Cancer Research UK, Department of Medical...

Present Applications

Contrast-enhanced MRI, particularly DCE-MRI, is the method of choice for monitoring response to pre-operative chemotherapy in certain malignant musculoskeletal tumors. DCE-MRI is broadly useful for detecting residual or recurrent tumor after surgery (van der Woude and Egmont-Petersen 2001 Ma et al. 1997 Verstraete and Lang 2000). The experience with DCE-MRI for staging local extent of these tumors and for planning biopsy procedures are discussed below under specific families of mus-culoskeletal...

Relaxation Enhancement

Biological tissues are associated with characteristic relaxation time constants T and T2, which reflect processes of longitudinal and transverse relaxation (often referred to as spin-lattice and spin-spin relaxation, respectively). These relaxation time-constants may indeed be directly interpreted as indicative of the nature of the microenvironment longitudinal relaxation is facilitated by (although not solely by) the presence of macromolecular or microstructural entities - hence water proton...

Clinical Application of Dcemri to Distinguish Malignant from Benign Soft Tissue Tumors

There have been several very recent reports of the utility of DCE-MRI in specific diagnostic questions and DCE-MRI-guided biopsy. The first two addressed challenges in distinguishing specific soft tissue malignancies from benign tumors. The first study looked at the DCE-MRI characteristics of synovial sarcoma (van Rijswijk et al. 2001). Synovial sarcoma classically occurs in soft tissues of extremities, especially near large joints, but can occur anywhere in the body, distant from joint spaces....

Measurement of Perfusion Using Bolus Tracking T2 MRI

As mentioned in Sect. 4.1, the effect of the contrast agent on the signal intensity on T2*-weighted images can be used to measure perfusion (Villringer et al. 1988 Rosen et al. 1990). This technique, usually referred to as dynamic susceptibility-contrast (DSC) MRI, is also known as bolus tracking. It involves the rapid injection of a bolus of paramagnetic contrast agent and the measurement of the transient signal loss during its passage through the tissue of interest (Fig. 4.1). Since the...

Clinical Experience

Both Kuhl et al. (1997a) and Kvistad et al. (1999) have evaluated the value of T2*W DCE-MRI for characterising breast lesions using visual assessments. Both studies showed strong decreases in signal intensity in malignant tissues whereas susceptibility effects in fibroadenomas were minor. Thus, it was possible to differentiate carcinomas from fibro-adenomas with high specificity using T2*W characteristics despite significant overlap in T1 enhancement patterns. The pathophysiological explanation...

Application of Dscemri in Enhancing Tissues

The standard analysis techniques for DSCE-MRI contrast bolus studies assume that the signal change observed results entirely from contrast within the blood vessels. However, leakage of contrast into the interstitial space will cause additional signal changes, principally by relaxivity mechanisms. The effects of relaxivity and susceptibility contrast mechanisms on the observed signal change are contradictory and successful application of DSCE-MRI techniques in enhancing tissues requires that...

Angiography

First, it is useful to consider angiography with conventional small molecular contrast media (SMCM). For these agents having molecular weights less than 1000 Daltons, there is a fast transendothelial diffusion resulting in a rapidly declining vessel-to-tissue contrast (Taupitz et al. 2000). Bolus tracking is also recommended when using SMCM to ensure that the image acquisitions are obtained with optimal timing, ideally just after the bolus arrives in the vessels (Bonk et al. 2000). However, the...

Clinical Considerations in Study Design

As one of the principal uses of DCE-MRI has been to investigate changes in the vasculature it is appropriate to consider the results of imaging studies in the context of an anti-angiogenic agent. Angiogenesis is the process of new blood vessel formation that is disordered in many pathophysio-logical conditions including cancer. In experimental models inhibition of angiogenesis has been associated with tumour growth restraint and even shrinkage while clinical studies of anti-angiogenic agents...

Correlation of Dynamic Enhancement with Histological Parameters of Angiogenesis

The studies previously described largely focused on the correlation of imaging parameters with patient outcome measures, e.g., tumor regression, tumor control, or survival. Because these tumors are not resected, there is no correlation with histopathological parameters. The correlation of imaging with histologic parameters has been investigated at the German Cancer Research Center in Heidelberg, Germany. Hawighorst et al. (1998) have examined the association of dynamic MRI parameters using...

Data Quantification and Limitations

Tracer kinetic principles can be used to provide estimates of relative blood volume (rBV), relative blood flow (rBF) and mean transit time (MTT) derived from the first-pass of contrast agent through the microcirculation (Rosen et al. 1991 Sorensen et al. 1997 Barbier et al. 2001) (Fig. 10.2). These variables are related by the central volume theorem equation (BF BV MTT). Quantification of T2*-weighted DCE-MRI and its application for leaky vasculature is discussed in detail elsewhere in this...

Info

Where Ce is the concentration of agent in ve, Cp is the concentration of agent in Vp, and Ktrans is the volume transfer constant between Vp and ve (ToFts et al. 1999). If the delivery of contrast medium to the tissue is ample (meaning that the rate of extraction of contrast agent via the leaky capillary wall is small compared with the rate of replenishment via perfusion), Ktrans is equal to the product of the capillary wall permeability and capillary wall surface area per unit volume, PSp. PS...

Enhancement Curve Analysis

A broad range of approaches have been taken to assess the properties of enhancement curves in various tumours (Kuhl and SchilD 2000). Most of these techniques are designed to deal with baseline variations in signal intensity and with the inherent differences in signal intensity that would be observed due to changes in tuning and scaling factors between scanners or even between sessions on the same scanner. Heywang and co-workers (1989) proposed a classification scheme for breast lesions using...

Lesion Characterisation Including Lobular Cancer and DCIS Evaluation

Lesion descriptors by morphological and kinetic features have been discussed in Sect. 10.4.1.3. Features that suggest the possibility of malignancy include a mass with irregular or spiculated borders, a mass with peripheral enhancement, internal heterogeneity and ductal enhancement. A rapid initial uptake of contrast agent followed by an early washout or heterogeneous signal intensity curve shapes are also features suggesting malignancy. Features suggesting benign disease include a mass with...

Pixel Analysis of MR Microcirculation Imaging

In several studies on investigating microcirculation parameters in cervical cancer (Gong et al. 1999 Mayr et al. 1996b Cooper et al. 2000 Yamashita et al. 2000), the parameter of signal intensity was averaged over the imaged tumor region resulting in a mean dynamic enhancement pattern, not accounting for regional variation in tumor microcirculation. However, the heterogeneity of tumor blood supply and oxygenation is a well-described phenomenon in cancer. Using the mean enhancement value does...

Pathophysiological Basis of Contrast Enhancement

Numerous studies using dynamic contrast enhanced MRI have demonstrated that malignant tumours gen erally show faster and higher levels of enhancement than is seen in normal tissue (Padhani 1999, 2002). This enhancement characteristic reflects the features of the tumour microvasculature which in general will tend to demonstrate increased proportional vascu-larity and higher endothelial permeability to the contrast molecules than do normal or less aggressive malignant tissues. Cancer can develop...

Primary Soft Tissue Sarcomas

Soft tissue sarcomas are rare malignancies, although the reported incidence is increasing (Shapeero et al. 2002). They are also a very heterogeneous group of cancers, whose pathologic classification has evolved dramatically over the past 30 years. The lineage and genetic features of some malignancies in this group are well understood (e.g., rhabdomyosarcoma), while for others even the cell of origin is a matter of debate. The classification of soft tissue sarcomas thus is something of a work in...

Categories of Contrast Agents

MRI contrast agents may be divided into four broad categories non-selective, partially selective, targeted, and activated. The most common agents are those of the non-selective group as they are those that are currently used clinically. Often referred to as extracellular fluid (ECF), or extravascular agents, these are typically small molecules ( 500 Da) administered intravenously and leading to both T and T2* shortening. This subcategory of contrast media includes those agents routinely used in...

Contrast Agent Relaxivity

Provided that the BMS shift is negligible, the relationship between relaxation rate (1 T and 1 T2) and contrast agent concentration can be predicted by the Solomon-Bloembergen equations (Gowland et al. 1992) where r1 and r2 are the spin-lattice and spin-spin relaxivity constants respectively and T10 and T20 are the spin-lattice and spin-spin relaxation times respectively in the absence of contrast material. These relationships have both been confirmed in vitro (Rosen et al. 1990 Donahue et al....

Water Exchange

In the discussion above, and indeed in many studies employing dynamic contrast-enhanced MRI in oncology, it has been assumed that tissues contain a single, homogenous, water population with well described MR properties that undergoes simple changes when subjected to a contrast agent. However, experiments from the early days of biomedical MR suggested that the situation is more complex than this (Hazlewood et al. 1974). Water is found in a number of different environments in a biological tissue....

Sources of Error

As mentioned in Sect. 6.4 of this chapter, major sources of error may include the common assumption of a straightforward signal change - contrast agent concentration relationship and of a standard arterial input function. Other factors that can significantly affect both the accuracy and the precision of kinetic modelling results include the blood haematocrit, contrast agent relaxivity, errors in T1 measurement, image artefact, in particular those caused by motion, model over-simplification and...

Issues for Single Centre Trials

Choice of field strength, imaging coils and patient set up - these must be appropriate to the trial. Does the manufacturer provide the sequences required for the trial This may be a particular problem when quantitative measurements are required, or when faster than usual measurements are needed, or when the protocol calls for an unusual combination of information, for example interleaved T1 and T2*-weighted information (d'Arcy et al. 2002). If a nonstandard sequence is required the...

Conclusion s and Future Directions

DSC-MRI has long been adapted into daily clinical use with the rapid 2D or 3D GE EPI being the most predominant method due to its sensitivity to contrast agent in both capillaries and larger vessels (Weisskoff et al. 1994), whereas the SE method is more rarely used since it is sensitive only to contrast agent within the capillaries. However, singleshot, GE EPI techniques for bolus tracking of the brain suffer from a substantial loss of resolution at the maximum of the bolus associated with the...

Hepatobiliary Contrast Agents

Hepatobiliary contrast agents utilise hepatic excretion mechanisms to produce hepatocyte uptake and biliary excretion of paramagnetic ions by binding them to appropriate ligands. Two agents, Mangafo-dipir trisodium (Mn-DPDP, Teslascan) and Gado-benate dimeglumine (Gd-BOPTA, Multihance) are commercially available and a third, gadoxetic acid (Gd-EOB-DTPA, Eovist) is in phase III clinical trials (see Tables 14.1 and 14.2). Mangafodipir is the first manganese complex that has been used as contrast...

Measurement of Contrast Agent Concentration In Vivo

To monitor the kinetic behaviour of a contrast agent in vivo it is necessary to link the changes in concentration to changes seen in MR images. Since most agents are known to alter both the spin-lattice and spin-spin relaxation rates of tissues it should be possible to infer their distribution by observing the influence on the MR signal. Since the concentration of Gd ions is known to be directly proportional to the change in 1 T (Eq. 5.1), a series of measurements of the T of a tissue as a...

Introduction and Role of Imaging

Prostate cancer is the most commonly diagnosed cancer in men in the United States of America with an estimated 198,000 new cases in 2001 (GreenleE et al. 2001). In the United Kingdom and the European Union, prostate cancer is the second most common cancer in men, with 20,000 new cases in the UK in 1997 (CRC 2001) and an estimated 134,000 new cases in the EU in 1996 (EUCAN). Substantial increases in incidence have been reported in recent years around the world, some of which can be attributed to...

MR Imaging of Bone and Soft Tissue Tumors

A broad consensus on diagnostic assessment of mus-culoskeletal tumors has emerged over the past decade. Radiographs, clinical data and MRI can narrow the differential diagnosis, and in some cases precisely diagnose the tumor type (Ma 1999 van der Woude et al. 1998a). However, biopsy is still required for accurate diagnosis of musculoskeletal lesions. Protocols for MR imaging and the intricacies of interpretation in diagnosing musculoskeletal lesions have been well described in recent reviews...