Sci-Fri AM: Imaging - 06: The role of body mass and gender in atlas construction for attenuation correction in PET/MRI

Attenuation correction (AC) in PET/MRI is difficult as there is no clear relationship between MR signal and 511 keV attenuation coefficients (μ) as there is with CT. One approach is to register a pre-defined atlas of μ to the PET/MRI for AC. However, the design of the atlas may strongly influence the quantitative accuracy of the AC. Here we compare 3 different atlas design approaches and evaluate their performance in an oncology patient population. The 3 strategies were: use of BMI-dependent atlases; use of gender-dependent atlases, and use of a gender- and sex-independent atlas. Seventeen patients were imaged with FDG PET/CT and subsequently scanned with 3T MRI. MR and PET/CT images were coregistered, CT scans converted to μ-maps, and the resulting MRI/μ-map paired data were used to construct 6 atlases: averaged male and female atlases, averaged BMI-specific atlases (obese >30, overweight 25-29.9, Normal 18.5-24.9), and a single atlas comprised of all patients averaged together. The atlases were then used for PET AC for patients not included in the construction of the atlas in a leave-one-out manner. Resulting PET images were compared to each other and to the gold-standard CT-based PET reconstructions across all voxels and tissue-specific regions (soft-tissue, bone, lung). Sex-specific atlases yielded best results (average relative percent error over the 3 VOIs = 0.4509) & BMI-based atlases yielded highest average relative percent error at 0.9340. In all cases, highest errors were in the VOIs located in the livers.

Modified-release recombinant human TSH (MRrhTSH) augments the effect of (131)I therapy in benign multinodular goiter: results from a multicenter international, randomized, placebo-controlled study

BACKGROUND

Recombinant human TSH (rhTSH) can be used to enhance (131)I therapy for shrinkage of multinodular goiter (MG).

OBJECTIVE, DESIGN, AND SETTING

The objective of the study was to compare the efficacy and safety of 0.01 and 0.03 mg modified-release (MR) rhTSH as an adjuvant to (131)I therapy, vs. (131)I alone, in a randomized, placebo-controlled, international, multicenter study.

PATIENTS AND INTERVENTION

Ninety-five patients (57.2 ± 9.6 yr old, 85% females, 83% Caucasians) with MG (median size 96.0, range 31.9-242.2 ml) were randomized to receive placebo (group A, n = 32), MRrhTSH 0.01 mg (group B, n = 30), or MRrhTSH 0.03 mg (group C, n = 33) 24 h before a calculated activity of (131)I.

MAIN OUTCOME MEASURES

The primary end point was a change in thyroid volume (by computerized tomography scan, at 6 months). Secondary end points were the smallest cross-sectional area of the trachea; thyroid function tests; Thyroid Quality of Life Questionnaire; electrocardiogram; and hyperthyroid symptom scale.

RESULTS

Thyroid volume decreased significantly in all groups. The reduction was comparable in groups A and B (23.1 ± 8.8 and 23.3 ± 16.5%, respectively; P = 0.95). In group C, the reduction (32.9 ± 20.7%) was more pronounced than in groups A (P = 0.03) and B. The smallest cross-sectional area of the trachea increased in all groups: 3.8 ± 2.9% in A, 4.8 ± 3.3% in B, and 10.2 ± 33.2% in C, with no significant difference among the groups. Goiter-related symptoms were effectively reduced and there were no major safety concerns.

CONCLUSION

In this dose-selection study, 0.03 mg MRrhTSH was the most efficacious dose as an adjuvant to (131)I therapy of MG. It was well tolerated and significantly augmented the effect of (131)I therapy in the short term. Larger studies with long-term follow-up are warranted.

Follow-up of low-risk differentiated thyroid cancer patients who underwent radioiodine ablation of postsurgical thyroid remnants after either recombinant human thyrotropin or thyroid hormone withdrawal

BACKGROUND

We previously demonstrated comparable thyroid remnant ablation rates in postoperative low-risk thyroid cancer patients prepared for administration of 3.7GBq (131)I (100 mCi) after recombinant human (rh) TSH during T(4) (L-T4) therapy vs. withholding L-T4 (euthyroid vs. hypothyroid groups). We now compared the outcomes of these patients 3.7 yr later.

PATIENTS AND METHODS

Fifty-one of the 63 original patients (28 euthyroid, 23 hypothyroid) participated. Forty-eight received rhTSH and serum thyroglobulin (Tg) sampling. A (131)I whole-body scan was performed in 43 patients, and successful ablation was defined by criteria from the previous study. Based on the criterion of uptake less than 0.1% in thyroid bed, 100% (43 of 43) remained ablated. When no visible uptake instead was used, five patients (four euthyroid, one hypothyroid) had minimal visible activity. When the TSH-stimulated Tg criterion was used, only two of 45 (one euthyroid, one hypothyroid) had a stimulated Tg level greater than 2 ng/ml.

RESULTS

No patient in either group died, and no patient declared disease free had sustained tumor recurrence. Nine (four euthyroid, five hypothyroid) had received additional (131)I between the original and current studies due to detectable Tg or imaging evidence of disease; with follow-up, all now had a negative rhTSH-stimulated whole-body scan and seven (three euthyroid, four hypothyroid) had a stimulated serum Tg less than 2 ng/ml.

CONCLUSIONS

In conclusion, after a median 3.7 yr, low-risk thyroid cancer patients prepared for postoperative remnant ablation either with rhTSH or after L-T4 withdrawal were confirmed to have had their thyroid remnants ablated and to have comparable rates of tumor recurrence and persistence.

Diagnosis of pyogenic pelvic inflammatory diseases by 99mTc-HMPAO leucocyte scintigraphy

Pelvic inflammatory disease (PID) is one of the major health problems of women of child-bearing age. Among the most serious complications of PID is the formation of a tubo-ovarian abscess (TOA). Early diagnosis of this condition may prevent serious surgical complications such as peritonitis and sepsis, which may be fatal. The purpose of this study was to investigate the efficacy of technetium-99m hexamethylpropylene amine oxime (HMPAO) leucocyte scintigraphy in the diagnosis of TOA. Twenty women with high clinical suspicion of TOA underwent 99mTc-HMPAO leucocyte scintigraphy. The labelling of leucocytes with 99mTc-HMPAO was performed according to a standard protocol. Scans were obtained at 1, 3 and 24 h following the injection of the labelled leucocytes. In eight cases the early and/or late scan was positive, in 11 cases it was negative, and in one case of ovarian cyst torsion, confirmed by laparoscopy, it showed slight uptake in the capsule of the cyst (false-positive). The sensitivity of 99mTc-HMPAO leucocyte scintigraphy was 100%, specificity 91.6%, positive predictive value 89%, negative predictive value 100% and overall accuracy 95%. It is concluded that leucocyte scintigraphy is a non-invasive, safe, physiological and accurate procedure for the diagnosis of TOA. The 24-h scan is crucial, since in some cases the abscess was not clearly visualized on the early scan. Leucocyte scintigraphy may reduce the need for CT, diagnostic laparoscopy and unnecessary invasive surgical procedures.

Bilateral idiopathic chondrolysis of the hip: a case report

A case of bilateral idiopathic chondrolysis of the hip is presented. Chondrolysis is a process characterized by progressive necrosis of the hyaline cartilage of the acetabulum and femoral head, resulting in secondary joint space narrowing and stiffness. A 14-year-old boy was followed during a 2-year period, and the diagnostic values of the different imaging methods (radiography, magnetic resonance imaging [MRI], and bone scintigraphy) were evaluated. Scintigraphic evidence of marked periarticular uptake and premature fusion of the epiphysis of the greater trochanter was a reliable indicator of chondrolysis. Furthermore, the bone scan could precede other imaging methods (radiography and MRI) in the diagnosis of the progression of the pathologic process, status of the remodeling activity, and early involvement of an opposite joint. Given the high sensitivity of bone scans and the high specificity of radiographic and MRI examinations in the diagnosis of acute chondrolysis of the hip, all three methods are valuable and should be used as complementary diagnostic tools.

Diagnosis of urinary leak following abdominal total hysterectomy using renal scintigraphy

Surgical trauma to the urinary system is a relatively rare complication following gynecological surgery. A case of urinary leak from rupture of the bladder following abdominal hysterectomy was diagnosed by Tc-99m-DTPA renal scintigraphy and confirmed by direct radio-isotopic cystography. Renal scintigraphic techniques should be very helpful in early diagnosis of surgical damage to the urinary tract.

Unilateral acute renal cortical necrosis: correlative imaging

Bilateral acute cortical necrosis is a rare form of acute renal failure characterized by necrosis of the renal cortex and sparing of the medulla. Little information on the imaging presentation of bilateral acute renal cortical necrosis is available. The enhanced CT appearance is pathognomonic and diagnostic. The unilateral presentation of acute cortical necrosis is extremely rare, and no imaging methods have been described. The authors chose to apply scintigraphic evaluation to this unique condition complementary to CT to confirm the diagnosis. Mercaptoacetylglycine (T3) was selected to assess tubular damage, in contrast to the pure glomerular agent DTPA. Evidence of some tubular function and clear delineation of the shrunken kidney was found. Conversely, in the DTPA study the kidney was not visualized. A DMSA scan was performed for assessment of viability of the renal cortex and showed a photopenic halo around the small area of the viable cortex of the upper pole. The halo sign represents a cortical loss. The visualization of the upper pole as evidence of cortical viability as a consequence of collateral blood flow from capsular vessels was seen on angiography. Radiographic and scintigraphic correlation of this rare condition may be an effective means to confirm the diagnosis and to establish the extent of involvement. However, contrast CT remains the preferred method in the diagnosis of acute cortical necrosis.