<p>Whereas the effect of size and coating material on the pharmacokinetics and biodistribution of iron oxide based contrast agents are well documented, the effect of these parameters on liver metabolism has never been investigated. The primary purpose of this work was to evaluate the effect of iron oxide particle size and coating on the rate of liver clearance and particle degradation using a rat model. </p><p>The magnetic and relaxation properties of five different iron oxide contrast agents were determined prior to the onset of the animal studies. The R2* values and the T1-enhancing efficacy of the agents were also evaluated in blood using phantom models. The results of these studies indicated that the efficacy of these agents was matrix and frequency dependent. Correlations between the R2* values and the magnetic properties of the agents were established and a new parameter, Msat/r1, was created to enable better estimations of contrast agent T1-enhancing efficacy in blood. </p><p>The bio-distribution of one of the agents was also evaluated to assess the importance of sub-cellular particle distribution, using an isolated rat liver cell model. Phantom models were also used to verify that materials with magnetic properties similar to the particle breakdown products (ferritin/hemosiderin) may induce signal reduction when compartmentalized in a liver cell suspension. The results revealed that the cellular distribution of the agent did not influence the rate of particle degradation. This finding conflicted with current theory. Additionally, the study indicated that the compartmentalization of magnetic materials similar to ferritin may induce significant signal loss.</p><p>Methods enabling the accurate determination of contrast agent concentration in the liver were developed and validated using one of the agents. From these measurements the liver half-life of the agent was estimated and compared to the rate of liver clearance, as determined from the evolution of the effective transverse relaxation rate (R2*) in rat liver. The results indicate that the liver R2* enhancement persisted at time points when the concentration of contrast agent present in the liver was below method detection limits. The prolonged R2* enhancement was believed to be a result of the compartmentalisation of the particle breakdown products within the liver cells. </p><p>Finally, the liver clearance and degradation rates of the five different iron oxide particles in rat liver were evaluated. The results revealed that for materials with similar iron oxide cores and particle sizes, the rate of liver clearance was affected by the coating material present. Materials with similar coating, but different sizes, exhibited similar rates of liver clearance.</p><p>In conclusion, the results of this work strongly suggest that coating material of the iron oxide particles may contribute significantly to the rate of iron oxide particle clearance and degradation in rat liver cells.</p>

<p>Three-dimensional rotational angiography (3D-RA) is an established method within the field of interventional neuroradiology. The method has also a great potential in other areas with a complicated arterial anatomy. The purpose of this study was firstly to develop an investigative protocol for 3D-RA in renal transplanted patients with threatening allograft failure in diagnosing stenosis in the transplanted renal artery; secondly the protocol was evaluated and compared with a modified protocol including reduced contrast medium load. Furthermore, the advantages of the 3D reconstructions compared to the angiographic images were evaluated, likewise if an extended angle of rotation reduced the artifacts in the 3D reconstructions. The two protocols were compared with regard to image quality and acute nephrotoxicity. The accuracy of Doppler ultrasonography and the result of percutaneous transluminal angioplasty (PTA) were also assessed.</p><p>3D-RA was consecutively performed in 57 renal transplanted patients with suspicion of renal artery stenosis. A significant stenosis was found in 49% of the patients. The 3D reconstructions profiled 43% of the transplant renal artery stenoses better than the angiographic images. An extended angle of rotation reduced the artifacts. There was no statistical difference regarding image quality between the two protocols, and the renal function was equally affected in both protocols. Doppler ultrasonography sensitivity was 100%; specificity was 48% and positive predictive value 67%. PTA had a technical success rate of 92% and a clinical success rate of 75% after 3 months.</p><p>3D-RA is a helpful supplement in cases with complicated vascular anatomy, especially when PTA may be indicated. The 3D reconstructions profile the course of the artery more frequently than the angiographic images and support PTA. The 3D reconstructions are degraded of artifacts. Sampling artifacts can be diminished by increased C-arm rotation and increased number of projections. The distortions caused by beam hardening remain to be solved.</p>

<p>Renal artery stenosis (RAS) is a potentially curable cause of hypertension and azotemia. Besides intra-arterial renal angiography there are several non-invasive techniques utilized to diagnose patients with suspicion of renal artery stenosis. Removing the stenosis by revascularization to restore unobstructed blood flow to the kidney is known to improve and even cure hypertension/azotemia, but is associated with a significant complication rate. </p><p>To visualize renal arteries with x-ray techniques a contrast medium must be used. In a randomized, prospective study the complications of two types of contrast media (CO₂ and ioxaglate) were compared. CO₂ was not associated with acute nephropathy, but induced nausea and had lower attenuation differences compared to Ioxaglate. Acute nephropathy was related to the ioxaglate dose and the risk was evident even at very low doses if the patients were azotemic with creatinine clearance <40 ml/min. </p><p>Evaluating patients for clinically relevant renal artery stenosis can be done utilizing several non-invasive techniques. MRA was retrospectively evaluated and shown to be accurate in detecting hemodynamically significant RAS. In a prospective study of 58 patients, evaluated with four methods for renal artery stenosis, it was shown that MRA and CTA were significantly better than ultrasonography and captopril renography in detecting hemodynamically significant RAS. The standard of reference was trans-stenotic pressure gradient measurement, defining a stenosis as significant at a gradient of ≥15 mmHg. The discrepancies were mainly found in the presence of borderline stenosis.</p><p>The outcome of percutaneous revascularization procedures showed a technical success rate of 95%, clinical benefit in 63% of treated patients, 30-day mortality 1.5% and major complication rate of 13%. The major complication rate for patients with baseline serum creatinine >300µmol/l was 32%. Our results compare favorably with published studies and guidelines.</p>

<p>Transcatheter Arterial Embolization (TAE) is a method in which a catheter is inserted into an artery under fluoroscopy guidance. By using material that creates a thrombus, inserted through the catheter, the artery can be occluded and the bleeding stopped.</p><p>Endoscopy is the treatment of choice in upper gastrointestinal (GI) bleeding, but 10% to 30% of patients rebleed and needs other treatment options. Post Partum Hemorrhage (PPH) may evolve rapidly and can become life threatening. Obstetrical treatment will manage most cases, but in some cases emergency surgery is needed and in the worst case hysterectomy.</p><p>The primary aim of this thesis was to evaluate the clinical usefulness, improve the TAE technique and compare the outcome of TAE with surgery used as “salvage therapy” in patients with upper GI bleeding. Evaluate TAE technique and the long-term effect on the menstrual cycle and fertility in severe PPH.</p><p>To evaluate the clinical usefulness 13 patients were treated with TAE after endoscopic treatment failure and 5 were treated for recurrent hemorrhage after emergency surgery. </p><p>The clinical outcome and mortality rate of 40 patients treated with TAE was compared with 51 patients treated with surgery of upper GI bleedings. </p><p>In 13 patients the ulcer was marked with placement of a metallic clip at endoscopy to be able to locate the exact site of the bleeding ulcer during the TAE procedure.</p><p>A retrospective study of 20 patients with severe PPH treated with bilateral TAE of the uterine artery was performed. </p><p>TAE was found to be effective and an alternative to emergency surgery for control of massive upper GI bleeding. The 30-day mortality was lower in the TAE group (3%) compared to the surgical group (14%). </p><p>By marking the bleeding ulcer at endoscopy using a metallic clip the site of bleeding could be identified on angiography without extravasation of contrast media.</p><p>No major impact on fertility or menstruation cycle was found in patients treated with TAE in PPH. TAE in PPH is safe and have no major long-term side effect. By using TAE in PPH hysterectomy can be avoided.</p>

<p>Living kidney donation is a clinical situation with unique features in the sense that healthy individuals voluntarily expose themselves to certain risks and inconveniences. Therefore, eliminating as much of the associated discomfort as possible is crucial. The primary aim of this study was to evaluate whether it is possible to use the examination with computed tomography (CT), which is essential to the investigation, also for determining the ratio of the two kidneys’ function – the split renal function. If possible, an examination with gamma camera renography could be excluded from the work-up. </p><p>To investigate this possibility, 27 subjects who had underwent CT and renography as part of kidney donor investigation were studied retrospectively. The quantity of contrast material in each kidney was considered proportional to that kidney’s function, and measurement was made in each of the two available contrast phases. The results were compared to the results from renography. A similar analysis was conducted in 38 patients investigated for suspected renal artery stenosis with CT and renography, including a study of an automatized method for the acquisition of data from CT. For further scrutiny, a respiratory triggered dynamic contrast-enhanced magnetic resonance imaging (MRI) examination was investigated in 26 individuals. Results of split renal function were compared with renography and with CT in a subgroup. To study the possibility of facilitating the data analysis with CT, a formula for approximation of the contrast attenuation was studied in 64 subjects. An analysis of the significance of choice of contrast phase was also conducted in 43 subjects. </p><p>Unsatisfactory agreement with renography resulted from the CT analysis of previous donors, partly due to technical shortcomings. However, the technique was recognized to have a potential value. In the subsequent material, the settings were improved, with beneficial effects on the agreement. Respiratory-triggered MRI generated high quality examinations of renal uptake and excretion, with results harmonizing well with renography and CT. The approximation formula applied to CT resulted in higher accuracy for renal volume assessment than with the automatic method, and an acceptable agreement of the split renal function estimate. </p><p>From the presented results, a revision of the current donor investigation protocol is suggested. CT gives sufficient information to exclude renography as a routine examination. In cases of uncertainty, renography is recommended for secondary evaluation.</p>

The purpose of this work was to improve the diagnosis of intracranial hemorrhage with MRI, using, among others, T2*-w GE sequences. Various sequences were tested in rabbits at two magnetic field strengths. Then, the most effective technique was applied to stroke patients. Experimental studies: The MR detectability of small experimental haematomas in the brain and of blood in the cerebrospinal fluid (CSF) spaces of 30 rabbits was evaluated. MRI examinations were performed at determined intervals. The last MR images were compared to formalin fixed brain sections and, in 16 rabbits, also to the histological findings. T2*-weighted GE sequences revealed all the intraparenchymal haematomas at 1.5 T, appearing strongly hypointense. Their signal patterns remained unchanged during the follow-up. Blood in the CSF spaces was best detected at 1.5T with T2*-weighted GE sequences during the first 2 days. FLAIR and SE sequences were rather insensitive. Clinical studies: MR examinations were performed at 1.5T, including T1- and T2-w SE, FLAIR and T2*-w GE sequences. In the first clinical study, 66 intraparenchymal hematomas (IPH) of different sizes and ages were examined. T2*-w GE sequence was the most sensitive. On all the sequences, we found a big variety of signal patterns, without a clear relationship to the age of the hematomas. In a second clinical study, MR examinations were performed to 83 patients with acute stroke: 43 presented acute IPH and 40 were used as controls. Old microhemorrhages (OMHs) were found in 60% of the patients with IPH, and in 15% of the controls. Conclusion: T2*-weighted GE sequences are capable of revealing very small intraparenchymal hemorrhages at any stage, and blood in CSF spaces during at least the first 2 days. The age of IPHs cannot reliably be estimated with MRI. We have found a correlation between the presence of OMHs and acute intraparenchymal hematomas.

The tumor vasculature is poor and heterogeneous which may result in inadequate oxygenation and changed energy status. In addition the balance between cell proliferation and the rate of cell death is disturbed, which results in tumor growth. The aims of this study were 1) to gain more insight into the relation between tumor vascularity, hypoxia, and proliferation in solid tumors, and 2) to study the changes and dynamics of tumor oxygenation in relation to the vascular architecture within individual tumors. For this purpose a double hypoxic marker method was developed, which was subsequently used to 3) determine the turnover rate of hypoxic cells in three different tumor models and 4) to study the effect of cytotoxic drugs on tumor hypoxia and cell death. Solid tumor models grown in mice were used. The tumor microenvironment was investigated with exogenous cell markers for hypoxia (pimonidazole and CCI-103F), cell proliferation (BrdUrd) and blood perfusion (Hoechst 33342). The vasculature and the exogenous cell markers were visualized with immunohistochemical techniques. The tumor sections were scanned and quantified with an image analysis systemconsisting of a fluorescence microscope, CCD camera and image analysis software. The spatial organization of hypoxia, proliferation, and tumor vasculature was analyzed in several xenograft lines. The study revealed two main hypoxic patterns that seemed to be the consequence of complex relations between vasculature, oxygen delivery, proliferation, and cell loss. The novel double hypoxic cell marker method, with sequential injection of two hypoxic markers, was developed to study dynamic changes of the tumor oxygenation. Based on varying injection intervals between the markers the hypoxic cell half-life was determined in three tumor lines, and ranged from 17 to 49 hours. Intra-tumoral changes in oxygenation status upon oxygen modifying treatments were measured with the double hypoxic marker method. Both decreased levels of tumor hypoxia after carbogen breathing (95%O2 and 5% CO2) and increased levels of tumor hypoxia, as a result of reduced tumor perfusion after hydralazine treatment was detected. Finally the double hypoxic marker assay was used to analyze the effects of the hypoxic cytotoxin tirapazamine in relation to the hypoxic cell population, which caused a reversible decrease of the hypoxic fraction. The results presented in this thesis now form the basis for further studies to identify subpopulations of cells that represent specific targets for therapy, and to investigate the effects of different treatment modalities.

Whereas the effect of size and coating material on the pharmacokinetics and biodistribution of iron oxide based contrast agents are well documented, the effect of these parameters on liver metabolism has never been investigated. The primary purpose of this work was to evaluate the effect of iron oxide particle size and coating on the rate of liver clearance and particle degradation using a rat model. The magnetic and relaxation properties of five different iron oxide contrast agents were determined prior to the onset of the animal studies. The R2* values and the T1-enhancing efficacy of the agents were also evaluated in blood using phantom models. The results of these studies indicated that the efficacy of these agents was matrix and frequency dependent. Correlations between the R2* values and the magnetic properties of the agents were established and a new parameter, Msat/r1, was created to enable better estimations of contrast agent T1-enhancing efficacy in blood. The bio-distribution of one of the agents was also evaluated to assess the importance of sub-cellular particle distribution, using an isolated rat liver cell model. Phantom models were also used to verify that materials with magnetic properties similar to the particle breakdown products (ferritin/hemosiderin) may induce signal reduction when compartmentalized in a liver cell suspension. The results revealed that the cellular distribution of the agent did not influence the rate of particle degradation. This finding conflicted with current theory. Additionally, the study indicated that the compartmentalization of magnetic materials similar to ferritin may induce significant signal loss. Methods enabling the accurate determination of contrast agent concentration in the liver were developed and validated using one of the agents. From these measurements the liver half-life of the agent was estimated and compared to the rate of liver clearance, as determined from the evolution of the effective transverse relaxation rate (R2*) in rat liver. The results indicate that the liver R2* enhancement persisted at time points when the concentration of contrast agent present in the liver was below method detection limits. The prolonged R2* enhancement was believed to be a result of the compartmentalisation of the particle breakdown products within the liver cells. Finally, the liver clearance and degradation rates of the five different iron oxide particles in rat liver were evaluated. The results revealed that for materials with similar iron oxide cores and particle sizes, the rate of liver clearance was affected by the coating material present. Materials with similar coating, but different sizes, exhibited similar rates of liver clearance. In conclusion, the results of this work strongly suggest that coating material of the iron oxide particles may contribute significantly to the rate of iron oxide particle clearance and degradation in rat liver cells.

Three-dimensional rotational angiography (3D-RA) is an established method within the field of interventional neuroradiology. The method has also a great potential in other areas with a complicated arterial anatomy. The purpose of this study was firstly to develop an investigative protocol for 3D-RA in renal transplanted patients with threatening allograft failure in diagnosing stenosis in the transplanted renal artery; secondly the protocol was evaluated and compared with a modified protocol including reduced contrast medium load. Furthermore, the advantages of the 3D reconstructions compared to the angiographic images were evaluated, likewise if an extended angle of rotation reduced the artifacts in the 3D reconstructions. The two protocols were compared with regard to image quality and acute nephrotoxicity. The accuracy of Doppler ultrasonography and the result of percutaneous transluminal angioplasty (PTA) were also assessed. 3D-RA was consecutively performed in 57 renal transplanted patients with suspicion of renal artery stenosis. A significant stenosis was found in 49% of the patients. The 3D reconstructions profiled 43% of the transplant renal artery stenoses better than the angiographic images. An extended angle of rotation reduced the artifacts. There was no statistical difference regarding image quality between the two protocols, and the renal function was equally affected in both protocols. Doppler ultrasonography sensitivity was 100%; specificity was 48% and positive predictive value 67%. PTA had a technical success rate of 92% and a clinical success rate of 75% after 3 months. 3D-RA is a helpful supplement in cases with complicated vascular anatomy, especially when PTA may be indicated. The 3D reconstructions profile the course of the artery more frequently than the angiographic images and support PTA. The 3D reconstructions are degraded of artifacts. Sampling artifacts can be diminished by increased C-arm rotation and increased number of projections. The distortions caused by beam hardening remain to be solved.

Renal artery stenosis (RAS) is a potentially curable cause of hypertension and azotemia. Besides intra-arterial renal angiography there are several non-invasive techniques utilized to diagnose patients with suspicion of renal artery stenosis. Removing the stenosis by revascularization to restore unobstructed blood flow to the kidney is known to improve and even cure hypertension/azotemia, but is associated with a significant complication rate. To visualize renal arteries with x-ray techniques a contrast medium must be used. In a randomized, prospective study the complications of two types of contrast media (CO2 and ioxaglate) were compared. CO2 was not associated with acute nephropathy, but induced nausea and had lower attenuation differences compared to Ioxaglate. Acute nephropathy was related to the ioxaglate dose and the risk was evident even at very low doses if the patients were azotemic with creatinine clearance &lt;40 ml/min. Evaluating patients for clinically relevant renal artery stenosis can be done utilizing several non-invasive techniques. MRA was retrospectively evaluated and shown to be accurate in detecting hemodynamically significant RAS. In a prospective study of 58 patients, evaluated with four methods for renal artery stenosis, it was shown that MRA and CTA were significantly better than ultrasonography and captopril renography in detecting hemodynamically significant RAS. The standard of reference was trans-stenotic pressure gradient measurement, defining a stenosis as significant at a gradient of ≥15 mmHg. The discrepancies were mainly found in the presence of borderline stenosis. The outcome of percutaneous revascularization procedures showed a technical success rate of 95%, clinical benefit in 63% of treated patients, 30-day mortality 1.5% and major complication rate of 13%. The major complication rate for patients with baseline serum creatinine &gt;300µmol/l was 32%. Our results compare favorably with published studies and guidelines.