Non-diagnostic CT Research Articles

The Correct Selection of Pitch for Optimal CT Scanning: Avoiding Common Misconceptions

Today’s state-of-the-art CT scanners include many features that aid in the selection of optimal technique parameters. Vendors offer solutions for choosing the optimal beam energy (tube voltage), automatic exposure control (AEC) via tube current modulation control, patient positioning within the gantry, and patient-specific contrast injection protocols. The trend seems to be leading to a “push button” CT scanner in which only the dose, noise level, and image sharpness, determined by the clinical indication, need to be prescribed. This trend will likely decrease the frequency of nondiagnostic CT scans. However, it should not mitigate the need to understand some of the fundamental relationships between acquisition parameters and dose. We illustrate the most common misconceptions concerning the selection of pitch in this article.

Using SUV as a guide to 18F-FDG dose reduction.

This article explores how one can lower the injected (18)F-FDG dose while maintaining validity in comparing standardized uptake values (SUVs) between studies. Variations of the SUV within each lesion were examined at different acquisition times. Our protocol was approved by either the Human Investigation Committee or the Institutional Review Board. All 120 PET datasets were acquired continuously for 180 s per bed position in list mode and were reconstructed to obtain 30-, 60-, 90-, 120-, 150-, and 180-s-per-bed-position PET images with registration to a single set of nondiagnostic CT images. Qualitative assessment of the images was performed separately for correlation. The SUV measurements of each lesion were computed and normalized to the 180-s acquisition values to create a stabilization factor. These stabilization factors were used to demonstrate a predictable trend of stabilization over time. The variances of the stabilization factors over the entire dataset, composed of several tumor types over a range of sizes, were compared for each time point with the corresponding 150-s time point using a 2-sided F test, which has similar values to the 180-s time point. The variance of the data decreased with increasing acquisition time and with increasing dose but leveled off for sufficiently long acquisitions. Through the statistical analysis of SUVs for increasing acquisition times and visual evaluation of the plots, we developed and hereby propose an algorithm that can be used to seek the maximum reduction in administered (18)F-FDG dose while preserving the validity of SUV comparisons.

Detection of radioactive fragments in patients after radiological or nuclear emergencies using computed tomography and digital radiography

A comparison has been carried out between standard-dose computed tomography, non-diagnostic computed tomography and digital radiography with respect to their suitability for detecting radioactive fragments associated with nuclear or radiological events such as debris from radiological dispersal devices. The purpose was to investigate if radiographic imaging is justified for the detection and localisation of radioactive fragments in affected patients. Fragments of uranium (U), copper (Cu), iron (Fe) and volcanic ash with effective diameters ranging from (approximately) 100 to 700 μm were selected. The fragments were positioned at two different locations on an anatomical torso phantom and images were produced with standard-dose CT, non-diagnostic CT and digital radiography. Capsules with radionuclides of 137Cs, 60Co and 99mTc were also positioned in the phantom and the effective doses were estimated for radionuclide exposures as well as for standard-dose CT, non-diagnostic CT and digital radiography. For standard-dose CT and digital radiography, U, Cu and Fe fragments were detected in sizes down to 100–180, 250–300 and 300–400 μm respectively. For the non-diagnostic CT the results were 180–250 μm (for U), 300–400 μm (for Cu) and 400–500 μm (for Fe). The effective dose from the standard-dose CT, non-diagnostic CT and digital radiography was 5.6, 1.9 and 0.76 mSv. Corresponding doses from 137Co, 60Co and 99mTc positioned at the site of fragments were in the range of 0.07–0.1, 0.32–0.45 and 0.08–0.09 mSv per MBq during 24 h. We conclude that, for a number of gamma emitters with activity levels on the order of magnitude of megabecquerel, imaging using ionising radiation can be justified since the effective dose from the radionuclides will exceed the dose from the radiological examination.

Pediatric nuclear medicine and pediatric radiology

To improve clinical practice is our daily duty as specialists in radiology and in nuclear medicine. When a clinician asks us to perform an imaging examination, we have to advise that clinician about the best test or imaging strategy to study the clinical problem. Risk-to-benefit ratio and the ALARA principle have to be weighed, as well as modality and cost. Hybrid imaging is now the standard in nuclear medicine. The use of multimodality cameras such as SPECT/CT, PET/CT and PET/MR has been revolutionary [1–4]. The key is finding the exact location of functional or metabolic lesions. But adding CT increases the dosimetry [5–7], requires more detailed knowledge of imaging anatomy and depends on collaboration between radiologists and nuclear medicine specialists. The level of expertise among imaging specialists (at least in pediatric nuclear medicine) varies too much. In some countries nuclear medicine is an independent specialty, and in other countries radiologists are in charge of nuclear medicine tests. Physicians-in-training in radiology and in nuclear medicine have to receive multimodality training [8–12]. And continuing education in both specialties is vital to ensure that senior specialists are well-versed in the latest techniques. In any case, imaging specialists must be able to discuss the options with referring clinicians and to advise them on the appropriate technique for each clinical situation. Pediatric nuclear medicine can be performed in general nuclear medicine facilities or in dedicated pediatric nuclear medicine departments. The quality of the images has to be diagnostically excellent in pediatric nuclear medicine but superfluous scans must be avoided and doses must be as low as reasonably achievable and adjusted to each child according to international recommendations [7, 13–16]. These goals can be more easily reached in dedicated pediatric facilities. Dose reduction remains important. Contrary to general opinion the radiation dose of most nuclear medicine scans is lower than that of many comparable radiologic studies. The most typical example is abdominal CT, which has a higher dose than the most frequent nuclear medicine studies. Another example is that two-thirds of the radiation dose from PET/CT is from the CT component [12–14]. In the latter case it is possible to perform a diagnostic CT scan during the PET/CT examination rather than a separate diagnostic CT scan. Or a lower-dose CT scan could be performed in a patient who has recently undergone a diagnostic CT scan. The best option for the future in pediatric oncology, however, is PET/MR. In bone scintigraphy or an MIBG scan, performance of an SPECT/CT scan significantly increases the radiation dose [15–17]. A possibility is to use a lower-dose nondiagnostic CT scan in these cases. And the best practice is to report together with the radiologist, comparing the SPECT and the CT or MR images frame-by-frame. In many papers, correlative analysis of PET/CT images in children has been reported to be superior to separate analysis of CT and FDG/PET images. The term “correlative imaging” is the joint interpretation of different imaging modalities – CT, MR, US and scintigraphy [18]. This is the best example yet of why collaboration between radiologists and nuclear medicine physicians is so important.

P166 Role of Bronchoscopy in Patients with Haemoptysis and a Normal CT Scan

Aims and ObjectivesTo investigate the merits of conducting bronchoscopies in patients with haemoptysis and normal or non-diagnostic CT scan.MethodsUsing the in-hospital bronchoscopy reporting tool, a retrospective analysis was carried out...

42 The value of fibre-optic bronchoscopy in patients with haemoptysis and non-diagnostic CT scans

42 The value of fibre-optic bronchoscopy in patients with haemoptysis and non-diagnostic CT scans

Waiting to exhale: salvaging the nondiagnostic CT pulmonary angiogram by using expiratory imaging to improve contrast dynamics

We attempted to investigate whether computed tomography pulmonary angiography (CTPA) in the expiratory phase can improve contrast enhancement of the pulmonary arteries and mitigate the effect of inspiratory transient attenuation artifact, potentially salvaging nondiagnostic studies. Eighteen patients with indeterminate inspiratory CTPA, despite proper contrast bolus were studied. Patients were rescanned in expiration using the same contrast bolus and scanning parameters. The attenuation of each pulmonary arterial segment, superior and inferior vena cava, and atria and ventricles during the two phases of respiration was measured independently by three radiologists. All pulmonary segments were evaluated for filling defects during the two phases. In addition, the studies were graded for diagnostic quality of enhancement and probable impact on management. A statistically significant increase in pulmonary arterial enhancement was seen during expiration from the pulmonary trunk to the segmental pulmonary arteries (P < 0.001) and for the inferior vena cava, the right atrium, and the ventricle. The incidence of nondiagnostic inspiratory studies ranged from 89 to 100%, depending on the observer. All studies were upgraded to fully acceptable diagnostic quality with follow-up expiratory imaging (P < 0.0001). Expiratory phase imaging was observed to have diagnostic impact in 78 to 88% of cases, with overall good to moderate interobserver agreement. In one case, pulmonary embolism was detected on the expiratory scan, which was not seen on the inspiratory scan. Expiratory imaging for nondiagnostic CTPA improves pulmonary arterial enhancement and improves diagnostic quality of CTPA by eliminating transient attenuation artifact, thus facilitating more accurate diagnosis and providing earlier treatment of pulmonary embolism.

FDG-PET on irradiated brain tumor: ten years' summary

To evaluate FDG-PET in post-radiotherapy differentiation of tumor recurrence/malignant degeneration and radiation reaction, and to assess the role of PET in terms of survival. 117 consecutive patients with a total of 156 FDG-PET examinations with positive but non-diagnostic MRI and/or CT were included. Final diagnosis was based on histopathology or correlated with radiologic and clinical follow-up. Brain metastases from lung carcinomas were further studied separately. Survival time was analysed using the Kaplan-Meier method. There were 61 true-positive, 2 false-positive, 15 false-negative, and 51 true-negative PET examinations; 5 positive and 22 negative PET examinations were indeterminate. The positive predictive value of a PET examination was 96% in all and 100% in brain metastases from lung carcinoma. The negative predictive value based on the histopathologic results was 55.6%. Survival time was significantly longer in patients with negative PET. FDG-PET is a valuable tool in the detection of tumor recurrence, especially lung carcinoma metastasis. FDG uptake is a prognostic marker.

Contrast column interruption artefact in computed tomography pulmonary angiography

Interruption of the contrast column during inspiration can lead to non-diagnostic CT pulmonary angiograms. The importance of this artefact will increase with more CT studies being performed for pulmonary embolism on multidetector row CT. We describe here an instance of such an artefact and discuss its aetiology.

CT-guided Biopsy with Cutting-edge Needle for the Diagnosis of Malignant Lymphoma: Experience of 267 Biopsies

AIM: We performed a retrospective study of 267 core needle aspiration biopsies in order to estimate the accuracy of CT-guided aspiration core needle biopsies for the diagnosis and subsequent treatment of malignant lymphoma. MATERIALS AND METHODS: Between 1989 and 1999, 267 CT-guided core needle biopsies were performed in 241 patients with either primary or recurrent malignant lymphoma. Patients age ranged from 4--88 years. One hundred and sixty-six (62.2%) nodal and 101 (37.8%) extranodal aspiration biopsies were performed using either 18 G or 20 G Turner needles. Statistical method used was Chi-square analysis. RESULTS: An accurate histological diagnosis was made in 199 (82.5%) patients, the remaining 42 (17.4%) patients had non-diagnostic CT biopsies. Thirty-seven of them were diagnosed by a surgical biopsy, four by bone marrow biopsy and in one patient by paracentesis. One hundred and seventy-nine patients had non-Hodgkin's lymphoma (NHL) and 62 had Hodgkin's disease (HD); 23 (9.54%) patients underwent repeated CT biopsy which was diagnostic in 17 (73.9%) and non-diagnostic in six (26%). CONCLUSION: CT-guided aspiration core biopsies were sufficient to establish a diagnosis in lymphoproliferative disorders in 82.5% of cases. In the light of this experience we suggest that imaging-guided core needle biopsy be used as the first step in the work up of many patients with lymphoma Agid,R. et al. (2003). Clinical Radiology 58, 143–147.

Is unenhanced CT sufficient for evaluation of acute abdominal pain?

Background: To determine whether intravenous contrast improves the ability of radiologists to establish the cause of acute abdominal pain after nondiagnostic or normal unenhanced CT. Methods: Out of 164 consecutive emergency department patients presenting with less than 48 h of nontraumatic, acute abdominal pain, a confident diagnosis for cause of pain was made prospectively in 71/164 (43%) patients on these unenhanced scans by the monitoring radiologist. In the other 93 patients, our study sample, intravenous contrast-enhanced CT was obtained. At a later date, retrospectively, two experienced abdominal CT radiologists independently evaluated unenhanced CT scans alone for potential causes of pain and diagnostic confidence level on a 1–3 scale. At least 2 weeks later, intravenous enhanced and unenhanced scans were read side-by-side for the same assessment. Results: There was no significant difference in diagnostic confidence levels comparing unenhanced CT alone (2.59) vs. intravenous enhanced and unenhanced CT together (2.64). Chi-square analysis found no significant difference in finding a cause for pain when intravenous contrast was added compared to the initial unenhanced scan alone. Conclusions: Intravenous contrast did not significantly improve the ability of CT to establish a cause of abdominal pain after a negative or nondiagnostic unenhanced CT.

The Rehabilitation of Clinical Assessment for the Diagnosis of Pulmonary Embolism

Pulmonary angiography is the gold standard for diagnosis of segmental pulmonary embolism, but no longer for subsegmental pulmonary embolism because the inter-observer agreement for angiographically documented subsegmental pulmonary embolism is only 60%. A normal rapid ELISA VIDAS D-dimer test result and a normal perfusion scan exclude pulmonary embolism with a negative predictive value of >99%, irrespective of clinical score. The positive predictive value for pulmonary embolism of a high probability VP-scan compared to pulmonary angiography is 87% indicating that 13% of patients with a high probability VP-scan do not have pulmonary embolism. The combination of a negative CUS, a low clinical score, and a non-diagnostic VP-scan safely excludes pulmonary embolism. Patients with a non-diagnostic VP-scan, a negative CUS, but a moderate to high clinical score are candidates for pulmonary angiography. The positive predictive value of helical spiral CT is >95 to 99%. The combination of a negative CUS, a low clinical score, and the presence of a clear alternative diagnosis is predicted to safely exclude pulmonary embolism. Helical spiral CT detects all clinical relevant pulmonary emboli and a large number of alternative diagnoses in symptomatic patients with a non-diagnostic or a high-probability VP-scan. The negative predictive value during 3 months followup after a negative spiral CT for pulmonary embolism in 4 retrospective studies and 1 prospective management study was >99%. Only a small group of patients (1-2%) with a non-diagnostic spiral CT are candidates for pulmonary angiography. Therefore, it is predicted that the spiral CT will replace both VP-scanning and pulmonary angiography to safely exclude or diagnose pulmonary emboli in patients with suspected pulmonary embolism.

2. Diagnostic Utility of FDG-PET in the Clinical Management of Patients with Suspected Recurrent Pancreatic Carcinoma after Whipple Procedure

Purpose: We evaluated the usefulness of FDG-PET in the assessment of patients with suspected pancreatic carcinoma who have previously undergone a Whipple procedure.Methods and Materials: Attenuation-corrected FDG-PET was performed in 11 patients (5 males, 6 females, age range 52–76 years), with suspected recurrent pancreatic carcinoma after Whipple procedure. Recurrence was suspected based on clinical, laboratory (CA19-9 serum tumor marker level), or abdominal CT findings. Diagnostic validation was by histology in 2 patients and radiologic or clinical follow-up (5 to 48 months) in 9 patients. Changes in therapeutic management that were prompted by PET were tabulated.Results: PET was concordant with the findings of abdominal CT in 7 patients (6 true-positive, 1 true-negative). PET detected unsuspected lung lesions in 1 of these patients that was subsequently confirmed by a chest CT. PET was discordant with abdominal CT in 4 patients. PET detected tumor recurrence in 3 of 4 patients in this group (27% of total) who had non-diagnostic CT and elevated CA19-9 serology. Chemotherapy was initiated in 2 of these 3 patients (18% of total), while the other patient died shortly after the PET study from pneumonia and recurrent tumor was confirmed at autopsy. The remaining 1 of 4 patients in the discordant group had a false-positive PET study due to relatively high FDG localization in a displaced loop of bowel.Conclusion: PET is useful in localizing the tumor in post-Whipple patients with suspected recurrent pancreatic carcinoma and can impact their clinical management.

Uptake of Tc-99m sestamibi and Tc-99m MDP in anaplastic carcinoma of the thyroid (nondiagnostic CT and ultrasound scans).

A 63-year-old woman with hypothyroid disease was undergoing treatment with thyroid hormone. She had a bone scan for generalized bone pain and weight loss. The scan revealed a lytic lesion in the skull. Later a Tc-99m sestamibi scan showed thyroid uptake and infiltration into the neck structures. She underwent neck surgery with transoperative biopsy, which revealed anaplastic carcinoma, so a thyroidectomy was not performed. The surgical findings of the neck architecture were similar to those observed on the Tc-99m sestamibi scan. The skull radiograph, CT, and bone scan showed a skull lesion. CT and ultrasound of the neck revealed only atrophic changes (not diagnostic). The histopathologic findings of the skull biopsy were identical to those of the neck. The patient died 2 weeks after diagnosis.

The diagnosis of acromegaly: value of inferior petrosal sinus sampling.

The early diagnosis of acromegaly may be difficult when serum levels of growth hormone are minimally elevated and imaging of the pituitary gland fails to show an adenoma. However, transsphenoidal surgery has the greatest chance of cure at this stage. We therefore investigated the value of sampling petrosal sinuses for measurement of growth hormone in this group of patients. Simultaneous bilateral sampling of the inferior petrosal sinuses to measure serum concentrations of growth hormone was performed in five patients suspected of having acromegaly but with nondiagnostic CT scans (n = 5) and MR images (n = 3) of the pituitary gland. Levels of growth hormone from the petrosal sinuses were five to 36 times greater than levels in the peripheral veins in all five patients, and three of four showed a marked response to growth hormone-releasing hormone. During transsphenoidal surgery, growth hormone-producing microadenomas were resected completely in four patients. In the fifth patient, a left-sided microadenoma had invaded the cavernous sinus and could not be resected completely. Lateralization of the adenomas within the pituitary gland on the basis of differences in levels of growth hormone between the two petrosal sinuses was not completely reliable. Elevated levels of growth hormone in selective samples from the inferior petrosal sinuses can help support an early diagnosis of acromegaly when peripheral growth hormone levels and imaging are not diagnostic.

The neurophysiological aspects of electrical injuries.

Neurologic and psychologic studies were done on 16 victims of alternate current electrical injuries. The patients were followed for a period of over 5 years. The findings point to a stereotyped generalized cerebral dysfunction, resulting in depression, divorce, unemployment as well as a high incidence of atypical seizures (atonic and myoclonic seizures). The EEG and CT studies were nondiagnostic. Evoked potentials revealed abnormalities in the upper cervical spinal cord and lower brain stem regions, raising the possibility that the epileptogenic focus was too deep to be recorded by standard surface EEG recording. The fact that the electrical injury patients have a high incidence of severe emotional disturbance and post-traumatic depression along with atypical seizures, in the face of nondiagnostic EEG and CT studies, may result in improper management of such patients.

Plasma cortisol levels in lung cancer.

<b>90</b> <h3><b>Objectives:</b></h3> Fibrous dysplasia (FD) is a benign skeletal disorder characterized by the replacement of normal bone and normal bone marrow with abnormal fibro-osseous tissue leading to bone deformity, fractures, disability and pain. ¹⁸F-NaF is a bone seeking PET-radiopharmaceutical with favorable pharmacokinetics, which is taken up by bone through (¹⁸F-) ions exchange with hydroxyl ions (OH-) on the surface of hydroxyapatite. Bone areas of abnormally increased ¹⁸F-NaF activity reflect underlying processes characterized by increased bone surface exposed to blood flow, like the processes encountered in FD. Aim of the current study was to explore potential associations between the activity of ¹⁸F-NaF positive FD lesions in the entire skeleton with the serum levels of established markers of bone activity, such as alkaline phosphatase (Alk Phos) and osteocalcin (OC), and urine levels of N-terminal telopeptide (NTX). <h3><b>Methods:</b></h3> Fifteen FD patients underwent whole-body ¹⁸F-NaF PET/CT studies at the NIH Clinical Center (<b>Fig. 1A</b>). PET scans from the vertex of the skull to the plantar surface of the feet were obtained on dedicated PET/CT scanners, 62.36 ± 6.11 (mean ± SD) minutes (range: 58 - 76) after intravenous administration of an average ± standard deviation (SD) of 2.81 ± 0.83 mCi of ¹⁸F-NaF (range: 0.92 - 4.98). Low dose, non-contrast, non-diagnostic CT scans were acquired for localization and attenuation correction purposes. FD-related ¹⁸F-NaF activity was assessed by using MIM vista (version 6.5.9). Firstly, a VOI (volume of interest) encompassing the entire skeleton was drawn, and afterwards a SUVmax threshold-based approach -customized per patient- was employed in order to include all FD-related bone uptake. Automatic lesion demarcation generated by the software was compared with the lesions’ anatomic cross-sectional images, to achieve maximal overlap between functional and anatomic images. Separate VOIs encircling all areas above the SUVmax threshold set by the user, were automatically generated and areas with physiologic or non-FD related ¹⁸F-NaF activity (e.g. activity in the urinary tract) were manually removed by an experienced nuclear medicine physician. Subsequently, FD-related ¹⁸F-NaF activity in the entire skeleton determined as the product of SUVmean multiplied by the total volume (TV) of all skeletal ¹⁸F-NaF positive FD lesions (TA = SUVmean × TV) was obtained automatically. <h3><b>Results:</b></h3> Pearson’s correlation test revealed that FD-related ¹⁸F-NaF activity in the entire skeleton was positively associated with serum levels of alkaline phosphatase (r = 0.758, P &lt; 0.01) (<b>Fig. 1B</b>), osteocalcin (r = 0.707, P = 0.01) (<b>Fig. 1C</b>), and urine levels of NTX (r = 0.739, P = 0.02) (<b>Fig. 1D</b>). (P-values adjusted for false discovery rate) <h3><b>Conclusions:</b></h3> Skeletal FD-related ¹⁸F-NaF activity strongly correlates with bone turnover markers, indicating that ¹⁸F-NaF PET/CT imaging precisely reflects underlying bone metabolic processes encountered in FD. This data strongly implies the application of this imaging modality in the in vivo assessment of FD activity, holding promise to serve as a surrogate endpoint for accurate determination of disease activity.