Department of Radiology; Christian Medical College; Vellore, Tamil Nadu; India (Koshy, Livingstone)Department of Nephrology; Christian Medical College; Vellore, Tamil Nadu; India (Basu, John)
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Blood oxygen level–dependent (BOLD) magnetic resonance imaging (MRI) estimates tissue oxygenation by using the paramagnetic property of deoxyhemoglobin, utilizing it as an endogenous contrast agent. The partial pressure of oxygen within a tissue inversely corresponds with the amount of deoxyhemoglobin in it, which determines the rate of MRI signal loss in the region, quantified as the apparent spin-spin relaxation rate (R2*) (1). Calculation of the R2* value is an accurate and reproducible method of noninvasively estimating renal oxygenation, with very few artifactual errors (2). We used serial BOLD MRI to evaluate a patient with tuberculous abscesses in his graft kidney. This demonstrated a reduction in size of the abscesses, as well as a fall in R2* value within, as the patient showed clinical improvement on starting treatment.A 58-year-old diabetic man underwent a living-unrelated renal transplantation elsewhere in 2001 with prednisolone, cyclosporine, and mycophenolate mofetil but without induction therapy. There were no episodes of rejection while on follow-up with a baseline serum creatinine of 1.3 mg%. Since 2005, he had several episodes of bacterial urinary tract infection responding to antibiotics and underwent transurethral prostatectomy and endoscopic surgery for bladder neck narrowing in 2007. Since July 2008, he developed high-grade fever with sterile pyuria not responding to empirical courses of cefotaxime, magnamycin, or imipenem. There was an increase in serum creatinine (2.5 mg%), and he was referred for further management.On examination, he was febrile (102°F) with no localizing signs. Peripheral blood white blood cell counts were normal. Ultrasonography showed that the graft kidney contained multiple abscesses, one of which was aspirated, revealing numerous acid-fast bacilli. Urine and pus grew Mycobacterium tuberculosis. QuantiFERON-TB gold was negative, and the Mantoux test was nonreactive. There were no features of disseminated tuberculosis or infections caused by hepatotropic viruses, cytomegalovirus, or human immunodeficiency virus. The kidney donor was not traceable.The patient was treated with appropriately modified doses of isoniazid, ethambutol, pyrazinamide, and ofloxacin. Fever remitted in 5 days. He began to feel better and gain weight within a fortnight. He received pyrazinamide for 3 months and ofloxacin for 9 months, with isoniazid and ethambutol for 18 months to continue. By 3 months, he regained normal weight and renal function.A 3T Philips Intera Achieva MRI scanner (Philips, Netherlands) was used to perform routine T1-weighted and T2-weighted MRI sequences and BOLD imaging of the renal allograft after overnight fasting during the initial evaluation and follow-up visits. R2* values were calculated using the relaxation maps software tool v2.1 (IDLvm, PRIDE, Philips). A color-coded map based on the R2* value of each pixel was generated and displayed using a standardized color scale (3). The average R2* values within one of the abscesses was 7.8±0.5 before starting treatment. After starting treatment, the values became 3.5±0.2 at 1 month and 5±0.5 at 3 months. During the initial evaluation, at 1 month and at 3 months, the average R2* values in the cortex were 14.4±1.4, 16.2±1.2, and 16.1±1.3, and that in the medulla were 26.8±1.3, 30±1.2, and 27.2±1.4. (All these R2* values are described as mean value+standard deviation.)As the patient started improving on treatment, the poorly functioning area signifying the abscess cavity showed a reduction in size with alteration of shape and a decline in R2* value within, whereas T1-weighted and T2-weighted images showed only minimal changes (Fig. 1). Functional changes preceded morphologic changes as the abscess became gradually enclosed by normal functioning renal tissue. Prednisolone perhaps reduced the surrounding fibrosis as described by Haramaki et al.