- We have managed to scan a small group of 7 adult patients with follow-up CT examinations for malignant lymphoma (Hodgkin and non-Hodgkin) by using a low radiation dose and adaptive statistical IR and we have assessed the current studies in comparison with previous CT examinations scanned in full dose regimens,
with standard filtered-back projection.
- The scanner used for all examinations has been a GE Optima 64 slice and the iterative reconstruction technique was adaptive statistical iterative reconstruction (ASIR).The area of coverage comprised thorax,
abdomen and pelvis,
unenhanced and using 1mL/Kgbw isoosmolar iodinated contrast agent at 1.5-2mL/s flow rate (automated injector).
- Both standard and low-dose examinations included lung-type 1.25mm reconstructions (using a hard-type kernel filter).
- In the ASIR examinations have used only standard filters for abdomen,
pelvis and thorax,
but we have added a 2.5mm reconstruction on the entire area of coverage,
including the thorax.
- The low-dose ASIR examination has used one venous post-contrast phase (at 60s from contrast injection),
while standard explorations used two phases: one arterial (30s) and one venous phase (70s).
- The scanner used for all examinations was a GE Optima 64 slice and the iterative reconstruction technique was adaptive statistical iterative reconstruction (ASIR).
- A comparison of the scanning protocols relying on standard reconstruction and ASIR can be found in Table 1.
Table 1: Comparison between standard CT protocol and low radiation ASIR-based protocol in patients with hematological malignancies.
ASIR |
Standard |
Slice: 5mm/interval : 5 mm
|
Slice: 5mm/interval : 5 mm |
KV: 120; mA range: 80/400
|
KV : 120; mA range: 100/560 |
noise index 20; rotation time : 0.7s
|
noise index 11.57; rotation time : 0.7s |
dose reduction:
20% for patients ≥ 80 Kgs bw;
40% for patients < 80 Kgs bw
|
|
Recon 1 type: standard,
5mm thickness
ASIR for recon 1 : 20%,
30%,
40%,
50%,
60% (higher in patients with low body weight)
|
Recon 1 type: standard,
5mm thickness |
Recon 2 type: standard,
1.25mm thickness on lung areas (lung kernel) and 2.5mm on entire coverage area; ASIR for recon 2 : 60-80%
|
Recon 2 type: Lung (2.5mm thickness,
1.5mm interval) |
Patient age ranged from 45 to 70,
with an mean age of 60.
The diagnosis of the patients have been:
- diffuse non-Hodgkin lymphoma - 3 patients,
- peripheral T-cell lymphoma - 1 patient,
Hodgkin lymphoma with nodular sclerosis - 2 patients and
- Hodgkin lymphoma with mixed cellularity - 1 patient.
The findings that have been assessed in the studied patients,
both on standard FBP and ASIR examinations are listed in Table 2.
Table 2: Overall findings in studied patients
Finding |
# Occurencies (standard exams) |
# Occurencies (ASIR exams) |
Hepatomegalia |
4 |
4 |
Hepatic steatosis |
1 |
1 |
Intrahepatic bile ducts dilation |
1 |
1 |
Hepatic cysts |
1 |
1 |
Portal vein dilation |
1 |
1 |
Enlarged lymph nodes |
6 |
6 |
Splenomegalia |
1 |
1 |
Splenic vascular changes |
1 |
1 |
Adrenal hyperplasia |
1 |
1 |
Peripancreatic/mesenteric fat stranding |
3 |
2 |
Ascites |
0 |
1 |
Hiatal gastric hernia |
1 |
1 |
Bone demineralisation/osteoporosis |
1 |
1 |
Vertebral hemagioma |
1 |
1 |
Disseminated osteolytic lesions |
1 |
1 |
Pulmonary fibrotic lesions |
2 |
3 |
Pulmonary nodules |
2 |
2 |
Pulmonary compressive atelectasis |
1 |
1 |
Mediastinal mass |
1 |
1 |
Bronchiectasis |
1 |
1 |
Pulmonary emphysema |
1 |
|
Pulmonary interstitial lesions |
1 |
1 |
Fluid pericarditis |
1 |
1 |
Additional findings: one ASIR examination presented with important respiratory artifacts,
especially on the thoracic area,
relating to a difficult assessment of lung parenchyma.
According to data presented in Table 2,
the ASIR examinations provided diagnostic data in a similar manner to standard full-dose CT explorations.
- We have found that in only one instance,
peripancreatic and mesentery fat stranding (Fig. 1) have been marginally more difficult to assess by using the low-dose ASIR examination compared to the standard one,
but without any assessable effect on the clinical condition or outcome of the patient.
- In one patient,
a small focalised pulmonary lesion previously found on a standard exploration had undergone fibrotic peripheral changes,
apparently fully assessable in the low dose exploration (Fig. 2).
- One patient presented ascites only in the follow-up low dose examination.
- All enlarged lymph nodes,
mediastinal masses and parenchymal changes have been analysed with similar efficiency in both ASIR low-dose and standard full dose explorations (Fig. 3).
- No difference was noted in the analysis of bone structure (Fig. 3, Fig. 4).
- All ASIR low-dose explorations presented with slightly higher noise in all images,
regardless of the area of interest,
especially on the 2.5mm reconstruction (Fig. 6),
but no important lesion was missed or misinterpreted compared to standard-dose ones.
- Multiplanar reconstructions from the 2.5mm low-dose ASIR series (Fig. 7) have been found useful,
providing good quality images,
including in patients with higher body weight.
- We did not find any special requirement for using additional scans for assessing diffuse or focalised bone lesions.
- In one patient with high body weight we had to adjust the ASIR parameter at the lowest end of the range in order to obtain satisfactory images.
- Additionally,
we found that two postcontrast full-dose scan phases did not bring any additional diagnosis benefit in any of the assessed lesions compared to one postcontrast low-dose phase with ASIR reconstruction.
A comparative analysis of the radiation exposure of the patients undergoing the low-dose ASIR studies and the full-dose standard explorations is presented in Table 3.
Table 3.
Comparison of radiation doses received by patients after low dose ASIR studies and standard-dose explorations [numbers represent DLP values (mGy-cm)]
Patients |
ASIR |
Standard |
AC |
870.55 |
1630.00 |
CF |
483.88 |
612.71 |
CE |
1027.40 |
2141.00* |
CR |
836.22 |
1343.95 |
FF |
554.60 |
770.43 |
LM |
847.88 |
1223.00 |
MI |
469.67 |
826.26 |
TOTAL |
5090.20 |
8547.35 |
* The patient CE had undergone two other previous standard-dose CT examinations,
with DLP of 3103.00 and 3538 mGy-cm,
respectively,
not taken into consideration in above figures.
According to data in table 3,
the overall DLP value of our patients undergoing low-dose ASIR examinations is 59.553% compared to previous standard CT explorations,
meaning a reduction of estimated DLP of 40.447%.
The most important two limits of the study are represented by:
- the small number of patients and
- by the design of the study,
comparing two different CT explorations (related to radiation dose and reconstruction type),
each of them scanned at different times.
Unfortunately,
ethical considerations related to radiation safety did not allow us to perform two different scans (one full dose,
with standard reconstruction,
the other low-dose,
with ASIR) at the same moment,
for a more rigurous approach.