Recent Developments in Medical Imaging

The emergence of imaging techniques replaced the use of radiography in diagnosing disease conditions of the kidney. The new diagnostic imaging techniques such as Magnetic Resonance Imaging MRI, Ultrasonography, and Computed Tomography (CT scan) has been increasingly used in kidney disease diagnosis due to it’s non- invasiveness. The morphological information provided by these modalities can not be neglected.

Along with the advantages of the new imaging techniques though are the disadvantages thus analysis of the capabilities of the diagnostic imaging to be used as well as the significant researches that tested these image modalities needs to be considered before utilization of these techniques. The limitations of the other imaging modalities such as ionizing radiation, risks of nephrotoxicity in patients due to contrast medium that are nephrotoxic, and tissue differentiation that is of low quality are overcome by the Magnetic Resonance Imaging techniques.

Thru the use of MRI the patient is not subjected to ionizing radiation or nephrotoxic contrast agents as well as minimal invasiveness are gained by this diagnostic imaging modality(Perry and 2003). Magnetic Resonance Imaging (MRI) is increasingly utilized as a diagnostic imaging technique in evaluating chronic diseases of the kidney and Acute Renal Failure (ARF) because the technique makes possible the evaluation of the anatomy and function of this organ. MRI nowadays already permits ultrashort acquisition times thus the restriction of the use in MRI for ARF and chronic kidney diseases is already erased(Laissy, 2006).

MRI technology at present already branched into various modalities such as MR urography (MRU), MR functional imaging, MR angiography (MRA), and magnetic resonance spectroscopic imaging (MRSI)(Perry and 2003). MRU, MRA, MR functional imaging, and MRSI functions with the basic MRI principles but with additional features. Magnetic Resonance Angiography (MRA), a new technique that is developed with the principles of MRI has a significant value in monitoring transplanted kidneys (Clerbaux 2003).

The assessment of renal artery aneurysm, renal artery stenosis, and evaluation of the kidneys of donors in kidney transplants are recommended applications of MRA (Perry and 2003). The vascular anatomy of the newly transplanted kidney can be checked with the aide of MRA and without subjecting the patient to the negative effect of arteriography which is the patient’s exposure to ionizing radiation. This technique is with value in assessing the vascular anatomy of kidney transplants because of the non-invasiveness and three dimensional views that are characteristics of this modality(Clerbaux, 2003).

Renal stenosis diagnosis with MRA is 97 percent sensitive and 92 percent specific. MRA provides images that can be integrated to reconstruct a three-dimensional model of the viewed kidney and resulting images from this technique is of well developed quality (Perry and 2003). MRA when utilized to examine kidney graft arteries have the limitations regarding difficulty of exploration of the following: arteries with stents, distal segments of arteries, accessory arteries, arteries that are near metallic structures, and renal grafts with blocks.

MRA technique with three dimensional phase contrast has a disadvantage wherein blood flow artifacts will imitate blood vessel stenosis. Various developments in MRA modality such as the utilization of gadolinium injection, ultra rapid acquisition technique, and breath hold sections counteracts this problem while at the same time producing improved image quality. The diagnosis of transplanted kidney renal arterial stenosis (RAS) can not be relied solely on gadolinium enhanced MRA because this technique also false positive results(Clerbaux, 2003).

The results which are false positives can be attributed to the movements in the kidney that are associated with breathing or vascular pulsatile movements(Nadalo 2007). Thus it is recommended to countercheck the result with other imaging modality like Color Doppler Ultrasound when using gadolinium enhanced MRA in evaluating the presence of RAS in transplanted kidneys (Clerbaux 2003). The significant MRI types widely applied in diagnostic procedures for kidneys are plain multicontrast and contrast –enhanced MRI.

The commonly utilized contrast agents are ultrasmall superparamagnetic particles of iron oxide (USPIO) which is not yet available in clinical practice and non-specific gadolinium chelates(Laissy, 2006). Contrast media enhanced MRI avoids the toxicity of patients that is due to iodine in radiography with contrast agents. Contrast enhanced MRI with fast spoiled gradient-echo (FSPGR) sequences which is a material that enables three-dimensional imaging is an important modality utilized to assess the status of renal blood vessels and renal arterial diagnosis.

This technique aside from being able to evaluate the vascular system of the kidney is able to view the parenchyma also. Parts of the kidney such as the renal medulla and cortex, corticomedullary, and tubular nephrographic phases can be evaluated with this MRI that is enhanced with FSPGR technique. Studies proved that this type of contrast enhanced MRI has a significant value stenosis diagnosis and grading of inborn and transplanted kidneys(Heiss, 2000).

Non- invasive monitoring of the evolution of kidney diseases and provision of complete view of the kidneys are among the advantages of using MRI in kidney disease diagnosis. The MR angiography or venography utilization in uremic patients erased the risk of nephrotoxicity of these patients due to radiocontrast materials. Better understanding of the pathogenesis and intensity of the damage in cases of renal disease is achieved with the use of this imaging technique along with the newly developed contrast agents.

The diagnosis of kidney diseases is really improved with this modality(Laissy, 2006). Renal masses can also be diagnosed with the use of MRI which is clearly depicted when contrast enhancements incorporated into the technique. MRI with T1- weighted gradient echo sequences was utilized in the procedure. Masses in the kidneys such as angiomyolipomas which are tumors that is composed of smooth muscle, fat, and blood vessels in various amounts can also be diagnosed using MRI with T1- weighted gradient echo sequences and chemical shift MRI(Israel, 2005).

MRI though modality with so many advantages also contains disadvantages like the procedure is expensive, the time consumed in imaging is longer that might lead to patients being claustrophobic inside the machine, kidney stones are poorly visualized through this techniques, and not suitable for patients that has iron metal implant devices and foreign bodies(Perry and 2003). A problem that arises with the use of contrast agents in MRI is the risk of having nephrogenic systemic fibrosis (NSF) in patients with acute renal insufficiency and chronic or acute severe renal insufficiency due to the use of gadolinium-based contrast agents (GBCAs).

NSF is an incapacitating and can be fatal disease that affects the muscle, skin, and internal organs. Repeated exposure and higher dose of the GBCAs are risk factors that are involve in the development of nephrogenic systemic fibrosis. Food and Drug Administration of United States warns the consumers about the potential effects of GBCAs through requiring manufacturers of these types of products to indicate in their product’s boxes NSF warning signs. This agency also advices medical practitioners not to use gadolinium-based contrast agents if it is possible to have the diagnosis even with MRI that is non-contrast enhanced.

Patients also need to be educated about the nephrogenic systemic fibrosis prior to the use of gadolinium-based contrast agents(USFDA 2007). Another imaging modality that is widely used in the kidney disease diagnostics is Ultra Sound. This technique is more commonly used compared to MRI imaging and CT scan because of the availability and portability of the machine used in this imaging modality(Baxter, 2006). Evaluation of native (inborn kidney) and transplanted kidneys are facilitated with the use of Ultrasonography.

Among the capabilities of this imaging modality are the following: measuring size of kidneys and tumors; abnormality and tumor detection; visualization of swellings; and viewing of the appearance of the kidney(Sagireddy 2007). Benign cysts in kidneys can be diagnosed through this inexpensive imaging modality. Ultrasonography is 79 percent in sensitivity when used to detect small kidney carcinomas with a diameter that is below 3 cm (Francis IR et al. , 2005). A recent development in Ultrasonography which is the Color Doppler allows the evaluation of clots, pseudo-aneurysms, and any narrowing in the blood vessels of the kidney.

The main advantages of this procedure are the absence of contrast agents that may cause toxicity and absence of ionizing radiation which makes it a non-invasive technique. The machines for this diagnostic modality are also available in portable types and relatively cheaper when compared to machines used in CT scan and MRI techniques(Sagireddy 2007). The earliest imaging modality which is plain radiography or x-ray is still used today but to a limited extent due to the ionizing radiation which causes genetic mutations with repeated use.

The invasiveness of the procedure limits it’s utilization in diagnostic techniques to visualization and evaluation of kidney stones; and, rarely to determine the kidney’s shape and size. The non-invasiveness and absence of radiation of the new imaging modalities brought about a revolution in the field of imaging diagnosis. Improved visualization of organs is possible especially blood vessels that are not seen in radiography unless with use of contrast media.

The new diagnostic imaging techniques like MRI allow evaluation of kidneys to be transplanted and monitoring of the status of any transplanted kidneys(Nadalo 2007). The limitations identified in these non-invasive image modalities are continuously modified to achieve a technique that will be well suited for various diagnostic needs. The utilization of two or more diagnostic imaging modalities in kidney transplant examinations promotes counterchecking of results thus the diagnosis acquire a much more increased accuracy(Nadalo 2007).